Arctic Sea Ice : Forum

Cryosphere => Arctic sea ice => Topic started by: anonymous on February 04, 2013, 03:58:17 PM

Title: PIOMAS vs CryoSat
Post by: anonymous on February 04, 2013, 03:58:17 PM
I'm still digesting the latest thickness paper. It's a dense reading. Most importantly they draw a line from IceSat, several in-situ data measurement (moorings, submarine, icebridge) over CS2 to PIOMAS. Within an acceptable range it all makes sense, so PIOMAS is no longer just a modell working in a phantasy world, it's backed by real data from ground and orbit. Here a chart comparing CS2 with PIOMAS showing PIOMAS probably underestimates the seasonal amplitude:

(https://dl.dropbox.com/u/354885/Arctic/asinet/cs2-piomas.jpg)

The numbers might be a bit off to official PIOMAS data, because the paper mostly compares everything over the IceSat domain.
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on February 20, 2013, 09:48:43 PM
There was an interesting press release from the folks at UWash regarding the Cryosat-2 paper published in Jan 2013:

http://www.washington.edu/news/2013/02/13/european-satellite-confirms-uw-numbers-arctic-ocean-is-on-thin-ice/ (http://www.washington.edu/news/2013/02/13/european-satellite-confirms-uw-numbers-arctic-ocean-is-on-thin-ice/)

In particular, one of the paper's Authors, and PIOMAS investigators, has this to say:

“Other people had argued that 75 to 80 percent ice volume loss was too aggressive,” said co-author Axel Schweiger, a polar scientist in the UW Applied Physics Laboratory. “What this new paper shows is that our ice loss estimates may have been too conservative, and that the recent decline is possibly more rapid.”

Is it just me, or is this counter to the sea ice comparison chart from the paper, where Cryosat-2 data consistently shows slightly higher sea ice volume than shown by PIOMAS?

Have I got that wrong? Do the two use different domains? (coverage area) Is there a better interpretation of this statement? What have I missed?
Title: Re: Piomas vs. CryoSat
Post by: crandles on February 21, 2013, 12:01:46 AM

Is it just me, or is this counter to the sea ice comparison chart from the paper, where Cryosat-2 data consistently shows slightly higher sea ice volume than shown by PIOMAS?

Have I got that wrong? Do the two use different domains? (coverage area) Is there a better interpretation of this statement? What have I missed?

No you are right Cryosat 2 is higher than PIOMAS in both years, though perhaps not at 2012 minimum.

However look at the change over time - PIOMAS is showing no fall but cryosat 2 is showing 2012 lower than 2011. Perhaps it might appear a bit iffy to extrapolate one years change to the change over last 33 years. But this cryosat 2 evidence isn't the only evidence - remember the PIOMAS verification indicating that PIOMAS overestimated thin ice and underestimated thick ice. Now we can see that PIOMAS is about right at 2012 minimum then it follows that PIOMAS underestimates past minimums. So decline over the last 33 years is probably more than the 75% to 80% reduction in minimum volume since 1979 (16.855 down to 3.261 K Km^3).
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on February 21, 2013, 01:43:52 AM
So decline over the last 33 years is probably more than the 75% to 80% reduction in minimum volume since 1979 (16.855 down to 3.261 K Km^3).
Right Chris, that would be an 80.7% decline Dr. Schweiger refers to. But he goes on to say that the newly published data makes that 80% decline look too conservative. I still don't see that.
Anyone?
Title: Re: Piomas vs. CryoSat
Post by: TenneyNaumer on February 21, 2013, 03:22:22 AM
Hi everybody!  I just got back from Carnival in Rio!  Let the party begin! 
Title: Re: Piomas vs. CryoSat
Post by: TenneyNaumer on February 21, 2013, 03:43:06 AM
OK, that was a joke ::), but did you guys see this about the restrictions on publishing info related to a joint Canadian-U.S. research project to measure the ice in situ in order to verify CryoSat measurements:

http://www.cbc.ca/news/technology/quirks-quarks-blog/2013/02/loss-of-arctic-ice-loss-of-scientific-integrity.html (http://www.cbc.ca/news/technology/quirks-quarks-blog/2013/02/loss-of-arctic-ice-loss-of-scientific-integrity.html)

"...thanks to new confidentiality rules introduced into the U.S.-Canada project, both the Canadian scientists working at the Department of Fisheries and Oceans and the Americans may not be able to publish or distribute that data without [Canadian] government approval."
Title: Re: Piomas vs. CryoSat
Post by: Dromicosuchus on February 21, 2013, 06:33:51 AM
As it is, I'm not sure that there's much more to be gleaned from this than that PIOMAS is working pretty durn well, and that the calibrations of it using ICESAT worked, and didn't end up just being so much curve-fitting.  One might hazard a guess that the decline has been greater than shown by PIOMAS, based on the larger difference between the 2010 and 2011 minima, but based on just two years of data...Yeah, no.  "One" might hazard a guess, but "one" isn't going to be me.  Still, it's very good (in a "Oh goodness, we really are toast, aren't we?  It's not just the silicon nightmare of some dozing supercomputer, this is really happening in the real world" sort of way, granted) to know that PIOMAS appears to be working properly.

On another note, do you happen to know where I might find a link to the paper in question, Arcticio?  Is it trapped behind a paywall, or has it managed to sneak out of its cage?
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on February 21, 2013, 07:33:44 AM
On another note, do you happen to know where I might find a link to the paper in question, Arcticio?  Is it trapped behind a paywall, or has it managed to sneak out of its cage?

Hi D,

There's a pre-press version out (one of the Authors' server I suspect). Note that it is the accepted version of the paper, even though final formatting for the Journal is not done. Also note that all Tables and Charts are present at the end of the document. Here it is:

Laxon, S. et al. "CryoSat-2 estimates of Arctic sea ice thickness and volume." Geophysical Research Letters, 28 January 2013
http://www.personal.soton.ac.uk/pgc1g08/grl50193.pdf (http://www.personal.soton.ac.uk/pgc1g08/grl50193.pdf)

Also, read the Journal's Press Release for this paper at:
http://phys.org/news/2013-02-cryosat-mission-reveals-major-arctic.html (http://phys.org/news/2013-02-cryosat-mission-reveals-major-arctic.html)
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on February 21, 2013, 06:35:11 PM
I'm not going to rehash all of what I've already said at my blog:
http://dosbat.blogspot.co.uk/2013/02/cryo-sat-2-and-piomas.html

But it's worth noting from Table 1 of the Laxon paper that start volumes are relatively close for ICESat and PIOMAS in Feb/Mar. However for the start volume in Oct/Nov PIOMAS is 9119 km^3 for 2003 to 2008, while ICESat is around 12000 km^3. Once you adjust the figures for this large disparity in start volume the % decline figures for Oct/Nov are reasonably close at around 30%, that's between the 2003-2008 avg and 2012.

Artful Dodger,

It's not the author's server, I think it's been put up by Phil Chapman who's recently started commenting at Neven's blog. Note the 'pgc' in the URL, that's his initials. I suspect he's taking a bit of a risk, let's hope that URL stays below the radar.
Title: Re: Piomas vs. CryoSat
Post by: TerryM on February 21, 2013, 08:46:20 PM
OK, that was a joke ::), but did you guys see this about the restrictions on publishing info related to a joint Canadian-U.S. research project to measure the ice in situ in order to verify CryoSat measurements:

http://www.cbc.ca/news/technology/quirks-quarks-blog/2013/02/loss-of-arctic-ice-loss-of-scientific-integrity.html (http://www.cbc.ca/news/technology/quirks-quarks-blog/2013/02/loss-of-arctic-ice-loss-of-scientific-integrity.html)

"...thanks to new confidentiality rules introduced into the U.S.-Canada project, both the Canadian scientists working at the Department of Fisheries and Oceans and the Americans may not be able to publish or distribute that data without [Canadian] government approval."

This is a terribly important problem & I don't see it going away soon. If scientists in different countries can't collaborate, publish or even comment on their findings without the Canadian Government signing off at each step it's going to virtually shut down a huge amount of Arctic research - just when it's most needed.

I'd been aware of the crackdown within Canada, but now it's spread to anyone anywhere that has signed Canada on as a partner in their research.

As more information comes in this may be deserving of it's own thread.

Terry
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on February 21, 2013, 08:59:12 PM
Artful Dodger,

I suspect [pgc]'s taking a bit of a risk, let's hope that URL stays below the radar.

Thanks, Chris. I think the bird is out of the cage on that one. I found it with a search of the title on Google Scholar.  ::)
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on February 21, 2013, 09:18:05 PM
Pesky Google Search Bots!
Title: Re: Piomas vs. CryoSat
Post by: PhilGChapman on February 21, 2013, 10:56:54 PM
Consider it my #pdftribute (http://articles.washingtonpost.com/2013-01-16/lifestyle/36384043_1_academics-journals-copyrights/)  :)
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on February 22, 2013, 07:52:06 AM
Thanks Phil,  ::)
Title: Re: Piomas vs. CryoSat
Post by: Dromicosuchus on February 22, 2013, 08:00:30 AM
Many thanks for the link!  And yeesh, Arcticio, you were right; that is dense.  Very nice to have so much info on the methods used, though.  It'll be interesting to work my way through it.
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on February 23, 2013, 02:45:47 AM
In my continuing attempt to understand the Feb 13 Press Release from UWash/APL (and in the keenly felt absence of the rapier intellect and steady hand of blog commenter Peter Ellis ;) ), I have attached an annotated Figure 3 (see original up-thread) from the CryoSat2 paper to show the monthly decline in sea ice volume as estimated by CryoSat2 for each of 7 months.

As you can see, the line segments connecting the tops of each CS2 'triangle' in the chart show a decline for each month measured. Further, the slope of the monthly decline is steepest in the early Fall, and less severe for each successive month until peak volume is reached near the end of Winter.

So if I am interpreting the APL statement correctly, their reasoning goes to this argument: Given that CS2 measured GREATER volume loss from October 2010 to October 2011 than PIOMAS estimated as the volume loss, therefore PIOMAS is likely to be underestimating the volume loss.

Does that sound plausible? Your opinions? Peter sightings? Axel?
Title: Re: Piomas vs. CryoSat
Post by: Peter Ellis on February 23, 2013, 11:58:17 AM
Eh, it's pretty obvious what the press release is saying.  The rate of decline of autumn (edit: presumably October) ice as measured by satellite is even faster than the rate of decline modelled by PIOMAS. Moreover, they're not relying on just two years to make that conclusion.

From the abstract of the paper:

"Between the ICESat and CryoSat-2 periods the autumn volume declined by 4291 km3 and the winter volume by 1479 km3. This exceeds the decline in ice volume in the central Arctic from the PIOMAS model of 2644 km3 in the autumn, but is less than the 2091 km3 in winter, between the two time periods."

This is no more than was already said some months ago and discussed extensively by us and others back then.  I really don't know why everyone's acting surprised this time round.

In general, the satellite data seem to be reading slightly higher than the PIOMAS model, and also showing a somewhat wider seasonal cycle across the board.  This is not necessarily surprising because it's already known that PIOMAS tends to overstate thin ice and understate thick ice.  However, the satellite also has (potential) errors that work the same way.  Just as PIOMAS overstates thin ice, the satellite may understate it - PIOMAS models ice right down to ~25 cm thickness or even lower.  With a freeboard of only a couple of cm, that ice might not be seen at all by the satellite.  Conversely, just as PIOMAS understates thick ice, the satellite may overstate it: remember how it was showing thicknesses of up to 3m for the first year ice in Baffin Bay?  The suggestion at the time was that the satellite may have been confused by the overlying snow, or by thin icy layers within the snow.  Not having read the paper yet, I don't know if they fixed this issue.
Title: Re: Piomas vs. CryoSat
Post by: anonymous on February 24, 2013, 01:55:55 PM
I think CS2's accuracy mostly depends on proper estimation of snow load. 10cm of snow wrongly taken for ice adds apprx. 1m of ice thickness. From what I understand (please correct me, if needed) there are two approaches: 1) assuming the radar goes right through the snow and got reflected by the snow ice interface. The paper indicates this is not settled science:

Our assumption that the radar penetrates to the snow-ice interface is still the subject of investigation and may also introduce errors into bias our thickness estimates [Willatt et al., 2011 (http://discovery.ucl.ac.uk/1338049/1/1338049_Ku-band%20radar%20penetration%20into%20snow%20cover%20on%20Arctic%20sea%20ice%20using%20airborne%20data.pdf), pdf]

And 2) using data from weather models, like PIOMAS probably does to calculate heat flux. The CS2 QA site http://cryosat.mssl.ucl.ac.uk/qa/snowdepth.php?phase=Operational&baseline=B gives some insight, but I doubt it's actually used. See the image below from last August.

IIRC, I've also read somewhere a paragraph referring to kind of climatology with Arctic snow load, which might render useless if more open water leads to more humidity and more snow.

So, 1cm of snow can explain a lot of the ups and downs of CS2. So far I also assume wet snow and melting ponds totally mess up approach #1 and this is why there is no summer data.


(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fcryosat.mssl.ucl.ac.uk%2Fqa%2Fgetimage2.php%3Fimg%3Dsnowdepth%2Fdata%2F23_northpole_ALL_vals_B.png&hash=e536aa2c2820153ad359e5b8b974fd53)

Title: Re: Piomas vs. CryoSat - Error margins?
Post by: dlen on March 01, 2013, 03:16:06 AM
I did not read Laxon's paper thoroughly yet - what are the error margins, are they mentioned? This is not unimportant.

Schweiger et al gave +-1,35 1000 km³ for October PIOMAS values in their 2011 paper. This seems to have been too small.

Concerning all the calibration work with snow cover concerns, cracks, inhomogenities and the small tracked area per overflight, calculation of total volume is still a very indirect, intricate way of volume determination (though much better then mere simulation). Consequently, we remember the first publications in 2012 having been way off the mark and the work has taken an awful lot of time.
Title: Re: Piomas vs. CryoSat - Error margins?
Post by: Artful Dodger on March 01, 2013, 08:45:50 AM
Schweiger et al gave +-1,35 Mio km³ for October PIOMAS values in their 2011 paper. This seems to have been too small.

Hi dlen,

I estimate the difference CS2-PIOMAS for Jan 2012 to be <1300 km3. That month seems representative, except for Oct 2011 which has a much smaller difference.

That's well within the stated uncertainty for PIOMAS.
Title: Re: Piomas vs. CryoSat
Post by: dlen on March 01, 2013, 04:01:47 PM
Hmm, You may be right.

In this graph, where is the actual datum point in the triangles: in the center of gravity or in the center of the smallest containing rectangle? That would be    (y_max + y_min) / 2    ?  I think the latter, but I am not sure.

I want to digitize the graph and add it to the plot in commons.wikipedia.org.

Or is there somewhere a table of the values printed out?

Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on March 01, 2013, 06:00:23 PM
I'm not aware of any of the values in figure 3 being available tabulated.

But the PIOMAS values should tally with monthly averages which can be calculated from PIOMAS main series, this is dependent on whether they've used a subset area, not the full PIOMAS domain.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on March 01, 2013, 07:01:10 PM
And if they are using the "official" piomas figures.
Eg Massonnet et al use a corrected series:

We also use the Pan-Arctic Ice Ocean Modeling and Assimilation
System (PIOMAS, Schweiger et al., 2011) output for
sea ice volume estimates. This Arctic sea ice reanalysis is
obtained by assimilation of sea ice concentration and sea surface
temperature data into an ocean–sea ice model.We use an
adjusted time series of sea ice volume partly accounting for
the possible thickness biases in the reanalysis (A. Schweiger,
personal communication, 2012)
Title: Re: Piomas vs. CryoSat
Post by: Vergent on March 01, 2013, 07:29:01 PM
I hate to be a technocrat, but the arctic sea ice volume is in the kilo km^3 range, not the mega.
Title: Re: Piomas vs. CryoSat
Post by: dlen on March 02, 2013, 02:56:17 AM
Yeah, that was tiredness or something alike. Corrected.
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on March 02, 2013, 05:32:27 AM
...the arctic sea ice volume is in the kilo km^3 range, not the mega.

Thanks, Vergent. Fixed in my comment above.  8)
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on March 02, 2013, 09:28:26 AM
Here is the digitized plot data:
:

[[1]]
          x line_piomas
1  2010.539    8.511989
2  2010.622    5.195339
3  2010.708    4.200344
4  2010.790    5.365653
5  2010.881    7.633525
6  2010.962    9.587660
7  2011.041   11.308732
8  2011.124   12.868454
9  2011.211   14.006872
10 2011.292   14.643311
11 2011.380   14.437141
12 2011.460   12.285800
13 2011.541    7.794876
14 2011.621    4.729215
15 2011.711    3.904534
16 2011.792    4.890565
17 2011.881    7.346680
18 2011.960    9.524912
19 2012.041   11.237021
20 2012.122   12.733996
21 2012.210   13.863450
22 2012.292   14.732950
23 2012.381   14.670202
24 2012.457   11.927243

[[2]]
          x line_cryosat2
1  2010.790      6.844700
2  2010.881      9.892433
3  2010.960     11.165310
4  2011.038     12.483006
5  2011.122     13.962053
6  2011.210     15.692089
7  2011.288     16.274744
8  2011.787      5.249122
9  2011.879      8.996041
10 2011.957     10.788825
11 2012.040     12.249944
12 2012.119     13.648316
13 2012.208     14.723986
14 2012.288     15.907223


(in 1000 km3 of course)
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on March 02, 2013, 09:36:00 AM
And attached the plot. Red line is "official" piomas.

Title: Re: Piomas vs. CryoSat
Post by: dlen on March 02, 2013, 02:02:10 PM
So I understand: the "inofficial" PIOMAS volume (used for the publication) relates to a considerably reduced base area.? As the "official" value is so much bigger?
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on March 02, 2013, 03:02:22 PM
It is all in the paper:

"The data are restricted to the “ICESat” domain"
"Arctic sea ice volume (km3) for the ICESat domain"

As far as I can see figure 1 is the clearest definition of that domain.
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on March 02, 2013, 03:46:34 PM
Thanks Wipneus.
Title: Re: Piomas vs. CryoSat
Post by: dlen on March 02, 2013, 08:36:23 PM
Yes thanks from the lazybones.  :)

The authors give actually a coarse error assessment, when they write:

"Our present understanding of both the
satellite and in-situ data is insufficient to resolve any inter-satellite bias to a higher
degree of certainty, but we note that an inter-satellite bias of 10cm would result in an
error in volume of ~700 km³, much lessthan the change in volume between the two
time periods."

Taking into account the mean errors against "in-situ-measurments", namely:
leads to a thickness error estimate around 7 cm against those comparison data.

Remains to add the errors of those data sources themselves, which are given as +-10 cm (airborne EM, ULS), while for the airborne laser data, no error margin is given in the Laxon paper. As lazybones I take its error as the same +-10 cm.

AFAIK error margins add like (sigma_1² + sigma_2²)1/2, that would be then 12,2 cm. If we are more cautious and take +-10 cm as uncertainty for the in-situ-measurement-Cryosat-relation, we arrive at +-14,4 cm.

Under the assumption of homogeneity this yields together with the base area of 7.2 Mio km² a Cryosat volume error margin of +- 880 km³ or, more cautiously, 1040 km³.

Althoug this is the error margin of one value, the errors are probably not uncorrelated. This means, that I wouldn't expect the values jumping wildly over the whole error interval from one point to the next. It is more like a smaller value of point-to-point jumping added to some longer term shift of the curve.
Title: Re: Piomas vs. CryoSat
Post by: dlen on March 03, 2013, 02:19:22 AM
I'd like to add one comparison plot from Tamino, for the sake of completeness
 ( http://tamino.wordpress.com/2013/02/20/cryosat-2-confirms-stunning-arctic-ice-loss/ (http://tamino.wordpress.com/2013/02/20/cryosat-2-confirms-stunning-arctic-ice-loss/) )
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on March 03, 2013, 05:27:06 AM
I'd like to add one comparison plot from Tamino, for the sake of completeness
Yeah, probably not too helpful, since CS-2 has not released any data for Oct/Nov 2012 yet.

The last CS-2 data point, from the Laxon paper that Tamino refers to, is for April 2012. Yet the line graph above show data for Oct/Nov 2012.

Probably needs to be redone.  ;)
Title: Re: Piomas vs. CryoSat
Post by: dlen on March 03, 2013, 05:59:47 AM
I used Wipneus' digitized data to extrapolate on the bigger PIOMAS domain by this method

vcryobig = vpiobig * ( vcryosmall / vpiosmall )

..big are data on the bigger PIOMAS domain
..small are data on the ICESat domain
pio.. are PIOMAS data
cryo.. are CryoSat2 data

and worked it into

http://commons.wikimedia.org/wiki/File:Plot_arctic_sea_ice_volume.svg (http://commons.wikimedia.org/wiki/File:Plot_arctic_sea_ice_volume.svg)

This is somewhat courageous, but I hope the error introduced is kind of second order.
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on March 03, 2013, 02:50:04 PM
In this graph, where is the actual datum point in the triangles: in the center of gravity or in the center of the smallest containing rectangle?
Hi dlen,

I don't think it matters, since the circles and triangles are exactly the same height. Therefore the centers must also be the same.

That is why all I've done in my annotated graph is connect the tops of each figure. It should be as valid a comparison for rate-of-change as if you computed the center and connected those dots.  8)
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on March 03, 2013, 02:54:55 PM
I tried to reproduce the "PIOMAS on IceSat domain" values from the piomas gridded data.

First the PIOMAS grid with my best guess for the IceSat domain. Area is 7.17 Mm2, Laxon et al. give 7.2 Mm2.

(https://sites.google.com/site/arctischepinguin/home/piomas/grf/IceSat_on_Piomas.png)
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on March 03, 2013, 03:01:49 PM
And here is the result (attached):

Still a bit bigger, but the remaining difference can be explained by the uncertainty of the "IceSat domain", I think.
Title: Re: Piomas vs. CryoSat
Post by: dlen on March 05, 2013, 04:45:21 PM
@Artful Dodger: You are right, for the connection lines, one can take anything, but when You want absolute values to get the ratio, You need to know where Your datum point is.

@Wipneus: What do Ye think, how come Laxon et al published smaller PIOMAS volumes? Did they do a different run with a smaller base area? No, I don't think so.
Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on March 05, 2013, 05:33:50 PM
@Artful Dodger: You are right, for the connection lines, one can take anything, but when You want absolute values to get the ratio, You need to know where Your datum point is.
Hi dlen,

APL makes no guarantee about the absolute value of their data. Their strong claim is that they've captured the volume loss trend correctly. The recent CS-2 data supports the position that PIOMAS loss rates are probably too conservative.

Wipneus has extracted numerical data for you for both. What else is it that you are looking for?
Title: Re: Piomas vs. CryoSat
Post by: dlen on March 09, 2013, 06:43:24 PM
This is a misunderstanding - I am o.k. with the data I got.

Title: Re: Piomas vs. CryoSat
Post by: Artful Dodger on March 10, 2013, 12:15:41 AM
This is a misunderstanding - I am o.k. with the data I got.
Okay, cool.  8) Let us know if you find anything interesting!
Title: Re: Piomas vs. CryoSat
Post by: Ice Cool Kim on March 23, 2013, 09:36:37 PM
A***: So, 1cm of snow can explain a lot of the ups and downs of CS2. So far I also assume wet snow and melting ponds totally mess up approach #1 and this is why there is no summer data.

That is the main thing I don't get with this CS2 data. March is hardly "summer" and ice pools tend to refreeze in August.  They don't even manage to capture the one point either side of the extrema.

Also they should be able to distinguish melt pools from leads since most will be nearly the same height as the ice surface.

May be it's early days yet and they still have some issues to sort out but it's over 2y years since they've had actual data coming in to work on.  Seven dots per year is a bit disappointing.

Not having September data really limits how much use this is, even just for calibrating the range of the annual oscillation in PIOMAS.

Maybe I missed something but they don't even seem to comment on or explain the glaring hole in the coverage.

Title: Re: Piomas vs. CryoSat
Post by: Ice Cool Kim on March 24, 2013, 12:40:21 PM
 Dodger: The recent CS-2 data supports the position that PIOMAS loss rates are probably too conservative.


I don't think that one monthly dot in each of two years shows anything at all except rough agreement.

The very small drop in max CS2 is way smaller than the discrepancy between CS2 and PIOMAS , well below the uncertainly of the CS2 data and can not be deemed to "support" anything.

Don't try to read too much (ie anything) into something that is well below the significance of the data.

Title: Re: Piomas vs. CryoSat
Post by: anonymous on May 04, 2013, 02:10:56 AM
I'd like to point a post by Martin Doble at the French forum called 'Chantier Arctique'. He describes measurements needed to get a higher accuracy from CS2 results. As he explains the draft/freeboard ratio is highly variable, especially if acquired from deformed ice. Although deformed ice might be soon a specialty from the past the post is interesting:

Estimating sea ice thickness from its freeboard (http://chantier-arctique.lebonforum.com/t140-estimating-sea-ice-thickness-from-its-freeboard)

So far we can question the accuracy of detecting the ice-snow-interface and the correct draft/freeboard ratio of deformed ice. I see negative freeboard looming at the horizon, too. Do we need more buoys instead of satellites to get answers in time?
Title: Re: Piomas vs. CryoSat
Post by: pdjakow on May 04, 2013, 01:16:27 PM
I wonder if there are PIOMAS data in gridded dataset i.e. netCDF files...
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on May 04, 2013, 02:50:50 PM
I wonder if there are PIOMAS data in gridded dataset i.e. netCDF files...

Even better, they are available as flat FORTRAN data files. ;)

The but's are: only monthly files and not regularly updated every month.

Have a look at http://psc.apl.washington.edu/zhang/IDAO/data_piomas.html (http://psc.apl.washington.edu/zhang/IDAO/data_piomas.html)

Title: Re: Piomas vs. CryoSat
Post by: anonymous on May 06, 2013, 05:54:14 PM
ESA just released GBs of data from the CryoSat Cal/Val campaign and lowered access restrictions, here the list: https://earth.esa.int/web/guest/campaigns
Title: Re: Piomas vs. CryoSat
Post by: anonymous on June 17, 2013, 05:08:47 PM
ESA recently launched a CryoSat Wiki and Forum at https://wiki.services.eoportal.org/tiki-index.php?page=CryoSat%20Wiki

Registration starts top right, prepare to find a strong password :)

The Wiki is organized in five areas:

Documentation that provides a one shop stop for the most relavant CryoSat official Documents,  Technical Notes, Proceedings and News related to the mission

Publications that provides the links to a number of Publications and ESA Study Reports related to the mission

Thematic forums that provides an online discussion board where CryoSat users can post and follow threads over specific topics organized by System, Sea ice, Land ice, Ocean and Coastal zones

Resources that provides a repository of a number of useful links and software tools and readers related to the mission

Events, workshops and important meetings, providing links, minutes, presentations and reports when available
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 11, 2013, 02:33:16 PM
BBC's Jonathan Amos covers (http://www.bbc.co.uk/news/science-environment-23964372) the presentation of Cyosat 2 thickness data at Esa's Living Planet Symposium in Edinburgh and cites Prof Alan O'Neill: "What Cryosat has done in the past three years is to confirm the volume decline predicted by the modelling from the atmospheric record"

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fnews.bbcimg.co.uk%2Fmedia%2Fimages%2F69781000%2Fjpg%2F_69781046_marchapril.jpg&hash=777f7448b4160af938e85e4cef230a4f)
Title: Re: Piomas vs. CryoSat
Post by: Lennart van der Linde on September 12, 2013, 08:45:11 AM
Also see Joe Romm's post on this:
http://thinkprogress.org/climate/2013/09/11/2603711/arctic-death-spiral/ (http://thinkprogress.org/climate/2013/09/11/2603711/arctic-death-spiral/)

Did PIOMAS also say volume was record low this spring?
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 12, 2013, 09:14:28 AM
Also see Joe Romm's post on this:
http://thinkprogress.org/climate/2013/09/11/2603711/arctic-death-spiral/ (http://thinkprogress.org/climate/2013/09/11/2603711/arctic-death-spiral/)

Did PIOMAS also say volume was record low this spring?

No and certainly not significantly (more than the uncertainty).
Title: Re: Piomas vs. CryoSat
Post by: Neven on September 12, 2013, 11:29:37 AM
I believe SMOS had volume 8% lower than 2012 at the end of the freezing season.
Title: Re: Piomas vs. CryoSat
Post by: werther on September 12, 2013, 02:17:58 PM
From UniLeeds Pr Andrew Shepherd (through ThinkProgress 11092013):

“The volume of the sea ice at the end of last winter was less than 15 000 cubic km, which is lower than any other year going into summer and indicates less winter growth than usual.”

Interesting…PIOMAS in its graph has it on 21600 km3 mid April at maximum.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 12, 2013, 02:46:38 PM
Werther, the CryoSat domain is not the same as that of PIOMAS. Discussed in the beginning of this very thread.

See for instance this post (https://forum.arctic-sea-ice.net/index.php/topic,8.msg826.html#msg826), with the normal PIOMAS volume and the PIOMAS-volume-on-Cryosat-domain.

If I understand correctly, the data to compare are:

"spring"
year      Cryosat volume
2011     16.3
2012     15.9
2013     15.0
Title: Re: Piomas vs. CryoSat
Post by: werther on September 12, 2013, 04:51:55 PM
Thanks, Wipneus,

I thought it would be something like that, Like Bering Sea, SoOchotsk cut out.
Haven't read this thread much or forgotten about the content.

Looking back, I saw your Feb map on the Cryosat domain. It cuts out a lot of other peripheral seas: the CAA, Hudson, EGS, Barentsz and Kara!
Leaving only 7.289 Mkm2. according to my CAD 'Total Arctic Ocean' map.
Not hard to guess how it arrives on 15000km3. And I remember, a lot of the PIOMAS volume at maximum came from extent growth in the Baffin/Barentsz/Kara seas.

The wait will be for Cryosat to assess the effects of this summer on coming winter's volume...
Title: Re: Piomas vs. CryoSat
Post by: Lennart van der Linde on September 12, 2013, 05:14:57 PM
"spring"
year      Cryosat volume
2011     16.3
2012     15.9
2013     15.0

Ok, thanks, and what are the comparable PIOMAS-numbers, if they're available for 2013 in particular?
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 12, 2013, 06:25:43 PM
I would have to compute them from the PIOMAS gridded data like I did here (https://forum.arctic-sea-ice.net/index.php/topic,8.msg948.html#msg948).

Tomorrow.
Title: Re: Piomas vs. CryoSat
Post by: Lennart van der Linde on September 12, 2013, 08:43:14 PM
That's great, Wipneus, thanks.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 13, 2013, 07:43:34 AM
Here you are. My estimate of IceSat domain is earlier this thread.

Year     
CryoSat2
PIOMAS
on IceSat domain
201116.315.36
201215.915.35
201315.015.21
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on September 13, 2013, 02:50:46 PM
And what is the Cryosat volume for october/november 2012? Is it available? I can´t find the data...
Thanks  ;)
Title: Re: Piomas vs. CryoSat
Post by: Lennart van der Linde on September 13, 2013, 03:01:13 PM
Ok, thanks, so CryoSat and PIOMAS are getting closer in their results over these years/so far, and give almost the same number for this year's maximum. Only a little over 1% difference is way within both error/confidence ranges, as far as those have been estabilished for CryoSat (about 9% uncertainty range for PIOMAS and about 5-7% for CryoSat?).
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 14, 2013, 01:33:42 PM
I believe SMOS had volume 8% lower than 2012 at the end of the freezing season.

Indeed, the interesting thing is you only get from SMOS' brightness temperature to sea ice thickness by knowing the atmosphere record (like PIOMAS), notably ice temperature. However, SMOS only works up to ~0.5m thickness. I remember the 8% figure too, but couldn't find the source, was CS2 data  already used? Nevertheless, PIOMAS having 11-13 April volume in the same ballpark makes me wonder.
Title: Re: Piomas vs. CryoSat
Post by: Vergent on September 14, 2013, 04:36:22 PM
arctic.io,

I think the -8% thickness number(Cryosat April) was reported in the "Sea Ice Outlook", unfortunately NSIDC is down till Monday. I hope everyone and the servers are all right.

Vergent
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on September 16, 2013, 05:54:03 PM
What do you think about the map for october/november 2012 recently released by ESA?:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fspaceinimages.esa.int%2Fvar%2Fesa%2Fstorage%2Fimages%2Fesa_multimedia%2Fimages%2F2013%2F09%2Fvariations_in_autumn_ice_thickness%2F13021431-1-eng-GB%2FVariations_in_autumn_ice_thickness.jpg&hash=7626be1670a074b191c6c7650e4cfcbc) (http://spaceinimages.esa.int/var/esa/storage/images/esa_multimedia/images/2013/09/variations_in_autumn_ice_thickness/13021431-1-eng-GB/Variations_in_autumn_ice_thickness.jpg)

Eyeballing the maps, 2012 seems very close to 2011...  :o
(maybe my eyeballing is wrong, a pixel counting could clarify it)
Is there a bias in this Cryosat map? Or is it real? Quick recovery of the sea ice extent and thickness after the record minimum of september 2012?

In PIOMAS data, the volume doesn´t rebound above 2011 until spring 2013... Who is right?
And curiously, in april 2013, when PIOMAS volume catchs up with 2011 and 2012, Cryosat shows the opposite...  :o

Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 16, 2013, 09:21:02 PM
Diablobanquisa,

It's all just variation within the error bounds for PIOMAS, not sure what Cryosat error bounds are but I'd assume the same there. I don't know what to make of it. But last year catching up with 2011/10 winter maxima isn't a surprise, although I think it's informative. This year and last show what impacts weather can have either way on the melt.
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on September 18, 2013, 01:47:44 AM

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fdiablobanquisa.files.wordpress.com%2F2013%2F09%2Fsin-tc3adtulo-9_html_62dfc16d.gif&hash=6e185d43f534b64cd50e19d512d7d607)

Sources:
Figure 5: http://imb.crrel.usace.army.mil/pdfs/kwok.ice%20thickness.jgr.2009.pdf (http://imb.crrel.usace.army.mil/pdfs/kwok.ice%20thickness.jgr.2009.pdf)
Table 1: http://www.personal.soton.ac.uk/pgc1g08/grl50193.pdf (http://www.personal.soton.ac.uk/pgc1g08/grl50193.pdf) (autumn: unajusted data; winter: adjusted data)

It´s a rough approximation, please don´t fire me...
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 18, 2013, 08:33:57 AM
Diablobanquisa,

There's something going on here but I'm not sure what. That comparison shows volume increase between the end of ICESat and start of Cryosat 2. Yet PIOMAS shows a drop in volume between those dates, and PIOMAS compares well with Cryosat 2 (the Laxon paper), and with ICESat Schweiger 2011 "Uncertainty in Modeled Arctic Sea Ice Volume").
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 18, 2013, 09:32:46 AM
It is never wise (scientifically speaking) to compare numbers without considering their uncertainty.
Kwok et al specify a RMS (one sigma) error in volume of 2.28 [1000 km3] for fall, and 1.562  [1000 km3] in winter. When I was younger, I was never allowed to specify uncertainty in 4 decimals.
They also specify trends, but strangely enough without uncertainty. Perhaps it is the text somewhere that the derived trends numbers are meaningless.

Anyway, the difference between ice volume in fall is less than one sigma, and in winter well below two sigma. It cannot be said (meaningfully) that something is going on.
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 18, 2013, 09:44:57 AM
Wipneus,

I did do a rough calculation using the uncertainties, and by my calculations only by selecting the highest for Kwok and lowest for Laxon did I get a reasonable drop between the two series. Which lead me to suspect something else was going on. But I didn't go as far as reading off values and spreadsheeting so perhaps you are correct and there is no issue.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 18, 2013, 10:31:05 AM
Which lead me to suspect something else was going on. But I didn't go as far as reading off values and spreadsheeting so perhaps you are correct and there is no issue.

There is nothing personal here Chris, but the when I saw Diablobanquisa's graph for the first time, I wondered about the error bars. They make the visible discrepancies meaningful or not. When I figured out what the error bar size was, I concluded probably not. Even without considering uncertainties in CryoSat and PIOMAS nrs.

My idea is that Laxon deliberately used averaged IceSat numbers because the trend in them is questionable.
And with just the average + the Cryosat2 + PIOMAS there is little remarkable going on. Or do you still see some discrepancy?

BTW, I haven't calculated anything and certainly not spreadcheated ;)

Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 18, 2013, 02:49:12 PM
The meereisportal.de has a CS2 thickness map for March 2013:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.meereisportal.de%2Ftypo3temp%2Fpics%2Ffcef874c01.png&hash=8897c5735f1d1a2e1ac5fbe000f2bf06)

Regarding IceSat vs Cryosat, IIRC due to different orbits Icesat captured a full image within 3 month where CS2 only needs one month.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 18, 2013, 03:26:59 PM
The meereisportal.de has a CS2 thickness map for March 2013:

Thank you! They have the downloadable data as NetCDF files as well.
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 18, 2013, 03:39:59 PM
Wipeus,

I do see what you say, and my conclusion was using a calculator at 06:00 - so was far from sound. I was just treating it as an early morning 'can I solve it issue'. I think your idea regards average numbers is probably correct and you were correct to point out error bounds.

Nothing personal taken. But as for spreadcheating... Hey! That's what I do!


A***,

Thanks for that, it goes to show how blunt a tool PIOMAS is, there's much more small scale variation in the Cryosat image. But it does support the predominant FYI state of last winter. Unfortunate that that didn't lead to a massive melt this year. But the feed through of thicker ice into next March will be a good further test of Cryosat.
Title: Re: Piomas vs. CryoSat
Post by: werther on September 18, 2013, 03:46:11 PM
For that 'feed through', a good refreeze will be necessary, Chris. It remains to be seen whether '13-'14 is going to provide that.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 18, 2013, 04:30:24 PM
All this on a 720x720 EASE2 25km grid:

      radar_freeboard:long_name = "Sea-ice freeboard" ;
      n_valid_radar_freeboard:long_name = "Total number of valid radar freeboard data points inside one grid cell" ;
      sea_ice_thickness:long_name = "Sea-ice thickness" ;
      n_valid_ice_thickness:long_name = "Total number of valid sea-ice thickness data points inside one grid cell" ;
      sea_surface_anomaly:long_name = "Sea surface anomaly" ;
      radar_freeboard_uncertainty:long_name = "Radar_freeboard_uncertainty" ;
      ice_thickness_uncertainty:long_name = "Sea-ice thickness uncertainty" ;
      snow_depth:long_name = "Snow depth (modified climatology)" ;
      radar_penetration:long_name = "Maximum radar penetration into snow (parameterized)" ;
      ice_density:long_name = "Ice density (modified climatology)" ;
      snow_density:long_name = "Snow density (Warren climatology)" ;
      ice_type:long_name = "Sea-ice type" ;
      ice_concentration:long_name = "Sea-ice concentration" ;

Now lets start. EASE is equal area, so not the hassle with grid cell area calculation, hmm sounds too easy.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 18, 2013, 04:44:41 PM

Nothing personal taken. But as for spreadcheating... Hey! That's what I do!


The spelling checker did not like spreadsheeting either and suggested "spearheading"

I know that you use spreadsheets and I also know that you are happy with it.

Not for me though.

Can you handle NetCDF and HDF files?
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 18, 2013, 04:52:25 PM
Tried 4 tools to read the *.nc files, all give me invalid data for all variables. Asked via the contact form for a reply...
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 18, 2013, 04:59:48 PM
... there's much more small scale variation in the Cryosat image.
I suspect these are mostly artifacts of how the sensor scans the planets surface...

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fcryosat.mssl.ucl.ac.uk%2Fqa%2Fgetimage2.php%3Fimg%3Dseaice%2Fdata%2F34_northpole_ALL_vals_B.png&hash=20fb3d0a1947f705d08106ad39ea0974)
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 18, 2013, 05:25:35 PM

Nothing personal taken. But as for spreadcheating... Hey! That's what I do!


The spelling checker did not like spreadsheeting either and suggested "spearheading"

I know that you use spreadsheets and I also know that you are happy with it.

Not for me though.

Can you handle NetCDF and HDF files?

I've got an app that copies netcdf into Excel files, but haven't spent the time writing a macro to get the data into arrays because Excel 2007 can't handle massive files, and some of the data I've been looking at for NCEP/NCAR is in >100Mb files.

Arcticio is right that I should move to a better platform, but I balk at the time involved in learning a new language to the degree that I can use Excel and VBA.

On the subject of spellchecks, my blog's spell check doesn't like spreadsheet either, more weird is that it doesn't like the word blog.
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 18, 2013, 05:28:27 PM
Arcticio,

Looking at the meereiportal image above shows more of the sort of variation I'd expect. When I first saw the PIOMAS thickness data my initial response was surprise at it being so smoothed.
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 18, 2013, 05:45:17 PM
For that 'feed through', a good refreeze will be necessary, Chris. It remains to be seen whether '13-'14 is going to provide that.

I'm looking at trying to make a prediction for this winter's maximum volume. There's a relationship between autumn/winter volume growth and area/extent/volume at the minimum such that in recent years lower minimum leads to greater autumn/winter volume growth. I've done quite a few blog posts recently and want some time off, but my preliminary playing around with the data produces the following tentative figures- based on the three stated indexes at minimum, with a rough guess of 4.9k km^3 for the volume minimum.

NSIDC Extent 21.68 (0.52)
CT Area 21.62 (0.53)
PIOMAS Volume 22.79 (0.77)

The latter PIOMAS volume is the one I'm least happy with as the increased ice growth in autumn/winter isn't really related to volume but to the increasing amount of open water in the last few years. I've not worked out proper error bounds for those yet, the RMS error for the ten years used in each case is in brackets.

However I'm not sure I'm happy with the other calculations though - if CT Area and NSIDC Extent based calculations are correct then that suggests a lower maximum volume due to the growth/thickness response than over the last three years! Adding on the RMS error brings about 22.2k km^3, between 2011 and 2010, but closer to 2011 than 2010 - which fits my gut instinct better.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 18, 2013, 06:21:29 PM
Tried 4 tools to read the *.nc files, all give me invalid data for all variables. Asked via the contact form for a reply...

I have no problem (in R using ncdf4 lib). There are a *lot* of invalid grid cells, especially the ones that fall off the globe due to the projection: the earth's surface is a circle within the square grid.
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 18, 2013, 06:24:44 PM
Chris, I think I proposed a different platform 2 years ago. If you haven't spend the time improving Excel skills, you might have already gained enough time to develop a new part time hobby like fishing on top :) (pun intended)

Re. smoothness, an eye opener to me was the ice bridge data. Everything else looks heavily smoothed since then. The thing with CS2 is pixels side by side might have a time diff of 30 days, look the ray pattern following the latitudes.

Panoply lets me import these *.nc, but resists to plot them. An export of the thickness then starts like this:

196.27345,0.0,1.4E-44,2.8E-45,2.8E-45,1.8416428E34,1.009E-42,2.8E-45,7.366571E34 ... with NaNs spreaded without any system. Makes no sense at all.
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on September 18, 2013, 06:48:16 PM
Diablobanquisa,

There's something going on here but I'm not sure what. That comparison shows volume increase between the end of ICESat and start of Cryosat 2. Yet PIOMAS shows a drop in volume between those dates, and PIOMAS compares well with Cryosat 2 (the Laxon paper), and with ICESat Schweiger 2011 "Uncertainty in Modeled Arctic Sea Ice Volume").


PIOMAS vs. ICESAT+CRYOSAT

Fall (they are in quite good agreement):
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fdiablobanquisa.files.wordpress.com%2F2013%2F09%2Fimage0031-e1380128557291.png%3Fw%3D640&hash=226888f6dd49cff0b5d191f18e06059c)


Winter (there are some discrepancies):
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fdiablobanquisa.files.wordpress.com%2F2013%2F09%2Fimage0012-e1380128574103.png%3Fw%3D640&hash=e2293471d71119b9eedc388ac0e505b2)




Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 18, 2013, 07:16:08 PM

Panoply lets me import these *.nc, but resists to plot them. An export of the thickness then starts like this:

196.27345,0.0,1.4E-44,2.8E-45,2.8E-45,1.8416428E34,1.009E-42,2.8E-45,7.366571E34 ... with NaNs spreaded without any system. Makes no sense at all.

That is not good. Here the numbers that are not NaN, are  between 0.19583 and 7.548747.

(I opened 201303, the 201101 did not look too well on the website: incomplete)
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 19, 2013, 12:56:05 PM
Now lets start. EASE is equal area, so not the hassle with grid cell area calculation, hmm sounds too easy.
Equal area is nice to do the math, but plotting involves regridding, which consumes a lot of machine cycles and let the virtual machines I use in the cloud die. Don't tell me R does this out of the box.

How far are you already? Does AWI meets the CPOM results?

Here is a deep link into the archive showing all Cryosat data on maps: http://mep-datasrv1.awi.de/gallery/index.php?region=n&ice-type=thickness&maps=cryosat&minYear=2011&minMonth=1&maxYear=2013&maxMonth=4 (http://mep-datasrv1.awi.de/gallery/index.php?region=n&ice-type=thickness&maps=cryosat&minYear=2011&minMonth=1&maxYear=2013&maxMonth=4)
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 19, 2013, 06:50:51 PM
Now lets start. EASE is equal area, so not the hassle with grid cell area calculation, hmm sounds too easy.
Equal area is nice to do the math, but plotting involves regridding, which consumes a lot of machine cycles and let the virtual machines I use in the cloud die. Don't tell me R does this out of the box.

I don't see why you need regridding. Just plot pixel by pixel as x,y and there is a recognizable image. In fact I think the images on http://www.meereisportal.de/ (http://www.meereisportal.de/) are in this projection.
And yes, from an array called "sit", filled with sea ice thickness values, it is a one liner to create an image file:
:
writePNG(sit,"tmp.png")
The result with NaN's coded as white is attached. I also need a landmask in this projection for nice images, it does not seem to be in the nc files.

How far are you already? Does AWI meets the CPOM results?

I have been on the road all day, I came as far as calculating:

ice_concentration/100 * sea_ice_thickness [m] * 625 [km2]/106

This gives:
         date     volume
1  2011-01-15  4.9076324
2  2011-02-15 21.4862610
3  2011-03-15 24.0387541
4  2011-04-15 23.8183315
5  2011-05-15 19.2770542
6  2011-06-15  8.7775311
7  2011-07-15  0.3688989
8  2011-08-15  0.9055647
9  2011-09-15  2.1313803
10 2011-10-15  6.0696818
11 2011-11-15 13.7727295
12 2011-12-15 17.0248964
13 2012-01-15 17.6107925
14 2012-02-15 20.2405418
15 2012-03-15 21.4576165
16 2012-04-15 22.3840891
17 2012-05-15 18.6044975
18 2012-06-15  6.3298891
19 2012-07-15  0.2171291
20 2012-08-15  0.5552755
21 2012-09-15  1.7820316
22 2012-10-15  5.9148132
23 2012-11-15 12.4787856
24 2012-12-15 15.5528900
25 2013-01-15 16.0443608
26 2013-02-15 18.4534215
27 2013-03-15 22.4041133

So these data need to be restricted to the IceSat domain as well. The March 2013 value looks  not good. Suggestions welcome.

Here is a deep link into the archive showing all Cryosat data on maps: http://mep-datasrv1.awi.de/gallery/index.php?region=n&ice-type=thickness&maps=cryosat&minYear=2011&minMonth=1&maxYear=2013&maxMonth=4 (http://mep-datasrv1.awi.de/gallery/index.php?region=n&ice-type=thickness&maps=cryosat&minYear=2011&minMonth=1&maxYear=2013&maxMonth=4)

Thanks.
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 19, 2013, 07:03:44 PM
Arcticio,

It's just that I have so much on my plate, my list of papers to read keeps growing, and I've still got nowhere trying to use 2013 as a control to figure out what's causing the post 2007 summer atmospheric pattern. Maybe if the pack were behaving like it did 10 years ago I'd be able to make the time...
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 20, 2013, 12:02:31 AM
Chris, was just kidding. I have the same problem when I look what people do with R. But wasn't a butterfly in the Amazonas causing the weather patterns? Are you diving chaos theory?

Wipneus, yes, the landmask is it what forces me to regrid. I want SMOS, PIOMAS and CS2 all on same map (style). Plotting an aray works similar with Python.

Why is sea ice conc. in your formular? Was thinking it's already included (like thickness for complete grid point). Have to check the docs....
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 20, 2013, 08:22:26 AM
Wipneus, yes, the landmask is it what forces me to regrid. I want SMOS, PIOMAS and CS2 all on same map (style). Plotting an aray works similar with Python.

I see. I am actually considering moving my calculations to Python this winter. R is using too much resources to put on small server as is my intention.

Why is sea ice conc. in your formular? Was thinking it's already included (like thickness for complete grid point). Have to check the docs....

This is from the Laxon et al. paper:

In common with earlier satellite radar altimeters CS-2 sea ice thickness estimates
exclude open water [Laxon et al., 2003]. To compute sea ice volume we therefore
take the product of the area, the thickness excluding open water obtained from CS-2
and the ice concentration obtained from SSM/I

Laxon did not use the same data source, so in principle it is possible that "thickness" in the nc files means thickness averaged over the full cell surface. There is no indication in the NetCDF meta data that this is so though. The meta data is very meager anyway.
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 20, 2013, 01:40:08 PM
Wipneus, you're right, area * concentration * thickness = volume. Got it confirmed.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 21, 2013, 09:48:53 AM
I found EASE land masks at http://www.usna.edu/Users/oceano/ghenders/NASA/measures.php (http://www.usna.edu/Users/oceano/ghenders/NASA/measures.php)

With that a much prettier image (201303):
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on September 25, 2013, 08:42:28 PM
Diablobanquisa,

There's something going on here but I'm not sure what. That comparison shows volume increase between the end of ICESat and start of Cryosat 2. Yet PIOMAS shows a drop in volume between those dates, and PIOMAS compares well with Cryosat 2 (the Laxon paper), and with ICESat Schweiger 2011 "Uncertainty in Modeled Arctic Sea Ice Volume").


PIOMAS vs. ICESAT+CRYOSAT

Fall (they are in quite good agreement):
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fdiablobanquisa.files.wordpress.com%2F2013%2F09%2Fimage0031-e1380128557291.png%3Fw%3D640&hash=226888f6dd49cff0b5d191f18e06059c)


Winter (there are some discrepancies):
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fdiablobanquisa.files.wordpress.com%2F2013%2F09%2Fimage0012-e1380128574103.png%3Fw%3D640&hash=e2293471d71119b9eedc388ac0e505b2)


For further testing of the winter discrepancies, I have included the MYI area anomaly (rough numbers extracted from http://nsidc.org/arcticseaicenews/files/2013/04/Figure52.png (http://nsidc.org/arcticseaicenews/files/2013/04/Figure52.png) and ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/Mar/N_03_area.txt (http://ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/Mar/N_03_area.txt)):

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fdiablobanquisa.files.wordpress.com%2F2013%2F09%2Fimage0014-e1380134461314.png&hash=8c45ca95dc0aa5e379451218fb6f9f55)

Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 27, 2013, 08:33:35 PM
Diablobanquisa,

Thanks for that. It's lucky I popped in to see what's going on. I missed the post you quote.
Title: Re: Piomas vs. CryoSat
Post by: anonymous on September 28, 2013, 02:00:53 AM
I've found a recent presentation (http://epic.awi.de/33996/) about the German CryoSat data. It gives some interesting insights into error handling, but most importantly it details a bit on the 11-13 winter thickness trend, which is flat in PIOMAS and downwards with CryoSat.

(https://dl.dropboxusercontent.com/u/354885/Arctic/asinet/CS2-Winter.jpg)
   
Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on September 28, 2013, 12:37:37 PM
I've found a recent presentation (http://epic.awi.de/33996/) about the German CryoSat data.

Thanks arcticio. Very interesting! I note that additional information, including higher resolution graphics, is available from: http://www.meereisportal.de/cryosat (http://www.meereisportal.de/cryosat)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.meereisportal.de%2Ftypo3temp%2Fpics%2F7462018689.png&hash=3275e9769aae5610e5a68491c2513ec1)
Title: Re: Piomas vs. CryoSat
Post by: Steven on September 28, 2013, 03:35:09 PM
I've found a recent presentation (http://epic.awi.de/33996/) about the German CryoSat data. It gives some interesting insights into error handling, but most importantly it details a bit on the 11-13 winter thickness trend, which is flat in PIOMAS and downwards with CryoSat.
The presentation suggests that snow cover on top of the sea ice is still a source of uncertainty for the CryoSat-2 thickness calculations.

They use climatological data (http://www.atmos.washington.edu/~sgw/PAPERS/1999_Arctic_snow.pdf) for the snow depth (with a few modifications).  So if the actual snow depth in the winter of 2012/2013 was reduced compared to the two preceding winters (as suggested by the patterns for sea level pressure (http://neven1.typepad.com/blog/2013/04/20122013-winter-analysis.html#more)), perhaps that explains part of the decline in the CryoSat-2 thickness over the last 3 winters.  It's hard to say since the recent results are not published yet.
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on September 29, 2013, 08:17:48 PM
Thanks Steven, that should have occurred to me before.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on October 11, 2013, 12:51:04 PM
Cryosat-2 in trouble?

(found here (https://wiki.services.eoportal.org/tiki-view_blog.php?blogId=6))

03 Oct 2013

CryoSat acquisition stopped

CryoSat SIRAL acquisitions stopped yesterday (2nd October) at 16:23:01 UTC due to an onboard issue which is under investigation.

Science measurements will resume as soon as possible but not earlier than the beginning of next week.

and

08 Oct 2013

CryoSat acquisition stopped - Investigation ongoing

Activities to recover from the platform problem experienced on Wednesday 02 October at 16:23:01 are ongoing according to plan. The SIRAL instrument still remains switched off.

CryoSat teams are working around the clock to resolve the anomaly and resume science measurements as soon as possible.

SIRAL (Synthetic Aperture Interferometric Radar Altimeter) is the main instrument on board CryoSat-2.
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on October 12, 2013, 10:33:09 PM
Damn, that's bad news.

Thanks Wipneus.
Title: Re: Piomas vs. CryoSat
Post by: anonymous on October 13, 2013, 12:32:48 AM
According to this message (https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/cryosat/news/-/article/cryosat-siral-acquisitions-resumed) Cryosat resumed its measurements. Haven't found any information whether there is any additional impact.

I had a look at the snow thickness maps used to calculate thickness. It seems snow cover depends on ice age, I have no idea why. Otherwise same ice age gives same snow height for 2012 and 2013. So, the missing thing is real snow data. Has anyone an idea besides GFS or ECMWF? I believe there is somewhere data - isn't PIOMAS using that to estimate flux and isolation?
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on October 13, 2013, 08:01:24 AM
Arcticio,

I must admit I was anticipating something more serious. I've got too used to satellites failing.

I haven't a clue about snow thickness matching ice age. PIOMAS uses NCEP/NCAR for snow depth, I think this is calculated from precipitation through the winter.
Title: Re: Piomas vs. CryoSat
Post by: Steven on October 13, 2013, 03:50:20 PM
The user guide at the meereisportal website gives a bit more explanation:

There are promising efforts to use passive microwave to estimate snow depth with different approaches, but the current processors uses snow climatology instead of remote-sensing data.
 

Warren et al., 1999 (http://www.atmos.washington.edu/~sgw/PAPERS/1999_Arctic_snow.pdf) established this climatology with results from drifting station mainly on multi-year sea ice collected over the past decades.  But since the Arctic Ocean shows a significant higher fraction of first-year sea ice, we follow the approach proposed by Kurtz et al., 2011 (http://onlinelibrary.wiley.com/doi/10.1029/2011GL049216/abstract) and multiply the climatological snow depth values over first year ice with a factor of 0.5.  Note: This approach is identical to Laxon et al., 2013 (http://psc.apl.washington.edu/zhang/Pubs/Laxon_etal2013_icevol_grl50193.pdf).  The climatology is given as a fit function for each month and only valid for the central Arctic Ocean.  Significant error may occur if this fit is used also for region farther south (e.g. Baffin Bay), however this is included in the data product for the reason of completeness.

Emphasis mine.

http://www.meereisportal.de/fileadmin/user_upload/Pictures/Meereisbeobachtung/cryoSat-2/AWI_CryoSat-2_Documentation_20130624.pdf (http://www.meereisportal.de/fileadmin/user_upload/Pictures/Meereisbeobachtung/cryoSat-2/AWI_CryoSat-2_Documentation_20130624.pdf)
Title: Re: Piomas vs. CryoSat
Post by: anonymous on October 13, 2013, 11:35:58 PM
Chris, me too as I saw the headline. ESA's stream of information could be better, however it tells they found something, now I wait for confirmation data is actually dropping in again.

Steven, good finding. I might have an explanation. Assuming all snow is gone in September and after a given cut-off date there is no FYI, I would say FYI simply starts later in the freezing season to accumulate snow. Whether 0.5 is close to reality is another question. What bothers me most is because of the snow climatology the 'near-real-time' aspect of Cryosat is gone. A trend can only be visible after years. At least within the range of snow min and max.

Hopefully detecting real snow height from space makes some progress soon. Having an exact measurement in March/April is really worth the effort.

Btw. the laser technology used by IceSat doesn't penetrate snow at all, it always returns freeboard including snow.
Title: Re: Piomas vs. CryoSat
Post by: dlen on October 15, 2013, 01:00:47 AM
I wonder if it would not have been wiser to build in a laser altimeter instead of this radar, which measures the height of a plane somewhere within the snow layer, as I read somewhere.
So absolute values from CryoSat2 have to be taken with great care , it seems to me.
Title: Re: Piomas vs. CryoSat
Post by: anonymous on October 15, 2013, 09:31:17 AM
Well, at least in Winter CryoSat works better (theoretically), because the radar can penetrate down to the ice surface. So, having both technologies ready at the same time should give exact snow height at least within a relevant time span. During the CryoSat Cal/Val campaign NASA and ESA cooperated fruitfully, hopefully that continues.

Actually, what's needed is kind of SnowSat :). May be SMOS can jump in, because snow has effects on the polarization: Snow thickness retrieval over thick Arctic sea ice using SMOS satellite data (http://www.the-cryosphere-discuss.net/7/3627/2013/tcd-7-3627-2013.html). I wonder whether the data of 3 satellites from 2 nations flying in an orbit of some hundreds of kilometers can be synced down to centimeters to measure real snow thickness? Sounds like an exciting challenge.
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on October 15, 2013, 11:54:28 PM
http://www.the-cryosphere-discuss.net/7/5051/2013/tcd-7-5051-2013.html (http://www.the-cryosphere-discuss.net/7/5051/2013/tcd-7-5051-2013.html)
Title: Re: Piomas vs. CryoSat vs. IceSat
Post by: anonymous on October 16, 2013, 02:57:30 PM
diablobanquisa, nice, was just about to link this paper here. It gives a very readable overview about the uncertainties of sea ice thickness retrieval. Not only snow cover, but sea ice density is a major unknown. The authors claim the huge difference between IceSat and the first CryoSat results may be explained by differently assumed density or more exactly the proportion of MYI/FYI, instead of melting.

(https://dl.dropboxusercontent.com/u/354885/Arctic/asinet/thickness-uncertainties.png)  (http://www.the-cryosphere-discuss.net/7/5051/2013/tcd-7-5051-2013.pdf)
Title: Re: Piomas vs. CryoSat
Post by: dlen on October 19, 2013, 04:14:47 PM
Concerning freeboard measurement I found the following quote (http://www.meereisportal.de/fileadmin/user_upload/Pictures/Meereisbeobachtung/cryoSat-2/AWI_CryoSat-2_Documentation_20130624.pdf (http://www.meereisportal.de/fileadmin/user_upload/Pictures/Meereisbeobachtung/cryoSat-2/AWI_CryoSat-2_Documentation_20130624.pdf), contains an extensive treatment of uncertainties)

At dry and cold conditions, the main reflector of Ku-Band signal of SIRAL should theoretically be the snow-ice interface. However results from validation experiments (Hendricks et al., 2010, Willatt et al., 2010, Willatt et al., 2011) have shown that the retracked elevation is often within the snow layer or sometimes the air-snow interface, e.g. by ground radar observations or comparisons between airborne laser and radar altimeter. Since validation data regarding penetration are sparse at basin scale, we apply a simplified parameterization which is taking into account seasonal changes.Therefore we introduce an additional penetration factor P, which describes the penetration of the radar reflection horizon. For the entire Arctic we assume a maximum  penetration of 23 cm from November till April, 11 cm for October and May, and 0 cm from June till September. The penetration factor is set to not exceed local snow depth.

Interpretation of the SIRAL height data is by no means trivial.
No I know, why the first significant sea ice volume paper took 2 years after commisioning of the satellite.

From the discussion there, one can guess the one-point-uncertainty as sigma ~~ 0.3 - 0.4 m or so.
The mean uncertainty is of course much lower. But the use of arctic-wide factors is prone to introduce systematic errors - any error there adds directly to the mean error.

Another source can be found here: http://chantier-arctique.lebonforum.com/t140-estimating-sea-ice-thickness-from-its-freeboard (http://chantier-arctique.lebonforum.com/t140-estimating-sea-ice-thickness-from-its-freeboard).
Title: Re: Piomas vs. CryoSat
Post by: anonymous on October 27, 2013, 10:31:06 AM
Re. snow. There is a NASA Snow Working Group (http://nasasnowremotesensing.gi.alaska.edu/background), specialized on remote sensing. Found a recent presentation (http://nasasnowremotesensing.gi.alaska.edu/sites/default/files/AGU_TownHallMeeting_AWN_penultimate.pdf).
Title: Re: Piomas vs. CryoSat
Post by: crandles on November 28, 2013, 04:58:13 PM
Will Laxon, S. et al.

Laxon, S. et al. "CryoSat-2 estimates of Arctic sea ice thickness and volume." Geophysical Research Letters, 28 January 2013
http://www.personal.soton.ac.uk/pgc1g08/grl50193.pdf (http://www.personal.soton.ac.uk/pgc1g08/grl50193.pdf)

update their numbers?
Any idea on when such information will be released?
Will small gap in data matter?
Title: Re: Piomas vs. CryoSat
Post by: nukefix on November 28, 2013, 05:34:31 PM
I wonder if it would not have been wiser to build in a laser altimeter instead of this radar, which measures the height of a plane somewhere within the snow layer, as I read somewhere.
So absolute values from CryoSat2 have to be taken with great care , it seems to me.
Lasers work well until they fail, which has been a big problem with IceSat. The big benefit of a radar altimeter is that it does not require cloud-free conditions..
Title: Re: Piomas vs. CryoSat
Post by: anonymous on November 28, 2013, 07:37:10 PM
Will Laxon, S. et al. update their numbers?
Any idea on when such information will be released?
Will small gap in data matter?
CPOM lost both scientists, Laxon and Giles, due to different accidents earlier this year. Apparently AWI took over and released monthly netCDF files, read about here (http://www.meereisportal.de/de/meereisbeobachtung/meereis_beobachtungsergebnisse/beobachtungsergebnisse_aus_satellitenmessungen/cryosat_2_meereisprodukt/).

Monthly maps till March 2013 are here: http://www.arctic.io/explorer/16C9//4-N90-E0/ (http://www.arctic.io/explorer/16C9//4-N90-E0/)

I expect new data after winter, may be April.
Title: Re: Piomas vs. CryoSat
Post by: R Tilling on December 04, 2013, 03:19:59 PM
Hi all,

I just wanted to respond to some of the points on this thread. Firstly although we lost our colleagues earlier this year, CPOM UCL are still working on CryoSat data. This is totally separate from the product that AWI has released, which has nothing to do with UCL.

We're constantly updating our estimates of sea ice volume with the newest data, and this will be presented at AGU next week by myself, so come along! The intention is then to publish the results early next year.
Title: Re: Piomas vs. CryoSat
Post by: Neven on December 04, 2013, 05:52:13 PM
Thanks for this information, Rachel. Good to see that you guys over at CPOM UCL are still working with CryoSat data. Please, let me know when results are released and I'll mention it over on the Arctic Sea Ice Blog.
Title: Re: Piomas vs. CryoSat
Post by: crandles on December 10, 2013, 04:50:35 PM
AGU session C54A-04.
Trends in Arctic Sea Ice Volume 2010-2013 from CryoSat-2
Rachel Tilling, ...

Satellite records show a decline in Arctic sea ice extent over the past three decades with a record minimum in September 2012, and results from the Pan-Arctic Ice-Ocean Modelling and Assimilation System (PIOMAS) suggest that this has been accompanied by a reduction in volume. We use three years of measurements recorded by the European Space Agency CryoSat-2 (CS-2) mission, validated with in situ data, to generate estimates of seasonal variations and inter-annual trends in Arctic sea ice volume between 2010 and 2013. The CS-2 estimates of sea ice thickness agree with in situ estimates derived from upward looking sonar measurements of ice draught and airborne measurements of ice thickness and freeboard to within 0.1 metres. Prior to the record minimum in summer 2012, autumn and winter Arctic sea ice volume had fallen by ~1300 km3 relative to the previous year. Using the full 3-year period of CS-2 observations, we estimate that winter Arctic sea ice volume has decreased by ~700 km3/yr since 2010, approximately twice the average rate since 1980 as predicted by the PIOMAS.

http://fallmeeting.agu.org/2013/scientific-program-2/ (http://fallmeeting.agu.org/2013/scientific-program-2/)
Title: Re: Piomas vs. CryoSat
Post by: crandles on December 10, 2013, 05:09:33 PM
Perhaps also of interest

   
C54A-07. Uncertainties in Arctic sea ice thickness and volume: New estimates and implications for trends

Arctic sea ice area, thickness and volume have decreased in the last decades, but these estimates rely on a number of geophysical parameters which introduce large uncertainties. In our study we quantify the contributions of sea ice density, snow load, and area uncertainties on both sea ice thickness and volume estimates. Sea ice freeboard retrievals from the laser altimeter onboard ICESat are used along with snow depth, sea ice density and area derived from remote sensed measurements, or based on climatological in-situ data.

Our results show that the estimates of sea ice thickness and volume are slightly influenced by uncertainties in sea ice area, while the choice of the ice density value has a major impact. Temporal and spatial patterns of snow depth become particularly important when deriving information about trends and inter-annual variability of sea ice thickness and volume. We find that the order of magnitude of sea ice volume uncertainties is about 10% of the total Arctic sea ice volume and is larger than those reported earlier, while trends within the ICESat period (2003 - 2008) are similar. Using a consistent choice of sea-ice density for the ICESat and CryoSat-2 (2010 - 2011) data we obtain a less dramatic sea ice loss than reported previously.

Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on December 11, 2013, 09:56:33 PM
Thanks Crandles, very useful.

Good to see you back.
Title: Re: Piomas vs. CryoSat
Post by: anonymous on December 16, 2013, 10:50:03 AM
BBC reports (http://www.bbc.co.uk/news/science-environment-25383373) CryoSat estimates for October 2013: 9000km³, last year was 6000km³. Apparently a lot of MYI survived in place, north of Canada.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fnews.bbcimg.co.uk%2Fmedia%2Fimages%2F71759000%2Fjpg%2F_71759601_cryosat_thickness2.jpg&hash=cf61d05a50510675b6903bd5373ae98b)
Title: Re: Piomas vs. CryoSat
Post by: Neven on December 16, 2013, 10:17:44 PM
Blog post up on the ASIB (http://neven1.typepad.com/blog/2013/12/cryosat-arctic-sea-ice-up-from-record-low.html).
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on January 25, 2014, 04:31:26 PM
In the Cryosphere (http://www.the-cryosphere-discuss.net/8/721/2014/tcd-8-721-2014.html), an interesting discussion paper is published on a improved retrieval algorithm for Cryosat-2. The reported results (in the abstract) are impressing: freeboard and ice thickness have much better agreement with IceBridge data. In ice thickness the differences are reduced from 1.351 m down to 0.182 m.

An improved CryoSat-2 sea ice freeboard and thickness retrieval algorithm through the use of waveform fitting

N. T. Kurtz1, N. Galin2,3, and M. Studinger1
1Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
2Earth System Science Interdisciplinary Center (ESSIC), University of Maryland, College Park, MD, USA
3NOAA, Silver Spring, MD, USA

Abstract. We develop an empirical model capable of simulating the mean echo power cross product of CryoSat-2 SAR and SARIn mode waveforms over sea ice covered regions. The model simulations are used to show the importance of variations in the radar backscatter coefficient with incidence angle and surface roughness for the retrieval of surface elevation of both sea ice floes and leads. The numerical model is used to fit CryoSat-2 waveforms to enable retrieval of surface elevation through the use of look-up tables and a bounded trust region Newton least squares fitting approach. The use of a model to fit returns from sea ice regions offers advantages over currently used threshold retracking methods which are here shown to be sensitive to the combined effect of bandwidth limited range resolution and surface roughness variations. Laxon et al. (2013) have compared ice thickness results from CryoSat-2 and IceBridge, and found good agreement, however consistent assumptions about the snow depth and density of sea ice were not used in the comparisons. To address this issue, we directly compare ice freeboard and thickness retrievals from the waveform fitting and threshold tracker methods of CryoSat-2 to Operation IceBridge data using a consistent set of parameterizations. For three IceBridge campaign periods from March 2011–2013, mean differences (CryoSat-2 – IceBridge) of 0.144 m and 1.351 m are respectively found between the freeboard and thickness retrievals using a 50% sea ice floe threshold retracker, while mean differences of 0.019 m and 0.182 m are found when using the waveform fitting method. This suggests the waveform fitting technique is capable of better reconciling the sea ice thickness data record from laser and radar altimetry data sets through the usage of consistent physical assumptions.

Citation: Kurtz, N. T., Galin, N., and Studinger, M.: An improved CryoSat-2 sea ice freeboard and thickness retrieval algorithm through the use of waveform fitting, The Cryosphere Discuss., 8, 721-768, doi:10.5194/tcd-8-721-2014, 2014.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on January 26, 2014, 10:26:49 AM
Some snippets from the discussion paper's conclusions.

The reduced differences are indeed large, all pointing at an overestimating of ice thickness:

Through comparison with Operation IceBridge data for
the 2011–2013 campaigns, this study has shown that fitting of the CryoSat-2 level 1B
waveforms using a physical model can be used to obtain improved results over the em-
pirical lead and threshold tracker (ELTF) methods which are similar to those used by
Laxon et al. (2013). The ELTF method was found to have respective mean freeboard
differences (CryoSat-2 – IceBridge) of 15.4 cm, 15.9 cm, and 11.9 cm and mean sea
ice thickness differences of 144.2 cm, 149.3 cm, and 111.9 cm. The mean freeboard
differences for the waveform fitting method were 2.2 cm, 2.5 cm, and 1.1 cm, and the
25 mean sea ice thickness differences were 20.6 cm, 23.3 cm, and 10.6 cm.

I am actually amazed about the differences. There is no way I can reconcile these with the uncertainty figures mentioned in Laxon et al.:

: Laxon et al.
Finally we compare CS-2, gathered between the 10th of March and 09th of April 2011, with ice thickness estimates computed using laser altimeter freeboard measurements from the NASA Operation IceBridge (OIB) mission gathered between the 16th and 28th of March 2011. CryoSat data acquired over the same dates in 2012 are also compared with IceBridge data gathered between the 12th of March and the 2nd of April 2012. We compare this data by gridding both CS-2 and the airborne data onto the same 0.4 latitude x 4 longitude grid as used for the EM comparison. The correlation (figure 3c) is lower (R = 0.608) than either the EM or ULS and the mean difference is -0.048±0.723 m.


Back to the TCD paper, the authors discuss remaining possible enhancements, further reducing uncertainties.
About snow thickness they say:

Lastly, an
evaluation of the IceBridge snow depth measurements needs to be done to improve
basin-wide snow depth on sea ice estimates. This has been done for a single season
of data (Kurtz and Farrell, 2011) compared to the snow depth climatology of Warren
et al. (1999), and for passive microwave retrievals of snow depth on sea ice for first year
ice (Brucker and Markus, 2013). The focus of a future study will be to utilize existing
observations to improve estimates of snow depth on sea ice to be used in the retrieval
of sea ice thickness from the CryoSat-2 time series.

Finally they are very satisfied with Cryosat's data:

Overall, this study has further demonstrated the capabilities of CryoSat-2 for the
retrieval of sea ice freeboard and thickness. The advantage of the retrieval processes
used in this study is that they are compatible with the laser altimetry record and show
that the two records can be reconciled to produce a more complete time series of sea
ice volume change. This has distinct advantages for the expected launch of the ICESat-
2 laser altimeter mission in 2017. The lifetime of CryoSat-2 is expected to overlap with
the ICESat-2 mission, as is the new Sentinel-3 radar altimeter mission. The combined
satellite radar and laser altimetry data provided by these missions will thus provide
unmatched information on the state of the Arctic sea ice cover.
Title: Re: Piomas vs. CryoSat
Post by: Neven on January 26, 2014, 10:54:25 AM
Thanks for this, Wipneus.

The ELTF method was found to have respective mean freeboard
differences (CryoSat-2 – IceBridge) of 15.4 cm, 15.9 cm, and 11.9 cm and mean sea
ice thickness differences of 144.2 cm, 149.3 cm, and 111.9 cm.

What are they saying here exactly? That CryoSat2 data so far has overestimated average ice thickness by over 1 m?
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on January 26, 2014, 11:49:16 AM
Thanks for this, Wipneus.

The ELTF method was found to have respective mean freeboard
differences (CryoSat-2 – IceBridge) of 15.4 cm, 15.9 cm, and 11.9 cm and mean sea
ice thickness differences of 144.2 cm, 149.3 cm, and 111.9 cm.

What are they saying here exactly? That CryoSat2 data so far has overestimated average ice thickness by over 1 m?

Yes, according to the ELTF method. And that method is supposed to be similar to those used by Laxon et al.  The "similarity" is detailed a bit, but not completely:

We note that several differ-
ences are present between the freeboard retrieval used by Laxon et al. (2013) and the
ELTF method used here. The primary difference is that Laxon et al. (2013) subtracted
a bias from the sea ice lead elevations by taking the difference between returns from
the ocean when sea ice is not present and returns from leads in the nearby ice pack.
This was done following Giles et al. (2007), but was not done in the ELTF freeboard
retrievals. Additional differences include (but are not limited to) the exact definition of
the first peak, as well as the use of a mean sea surface height data set in place of
the EGM08 geoid. Therefore, the comparisons done in this study are similar, but not
exact reproductions of methodologies. The purpose of the comparison is to highlight
the physical basis between differences in the retracking methods
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on January 26, 2014, 11:49:39 AM
Neven,

From my reading, not necesarily, because the CS2 data used different assumptions for different regions. Those figures are the result if consistent assumptions are used. So the aim of the paper seems to be to develop a less subjective method.

Thanks for posting the link Wipneus.
Title: Re: Piomas vs. CryoSat
Post by: crandles on January 26, 2014, 10:28:03 PM
Thanks for this, Wipneus.

The ELTF method was found to have respective mean freeboard
differences (CryoSat-2 – IceBridge) of 15.4 cm, 15.9 cm, and 11.9 cm and mean sea
ice thickness differences of 144.2 cm, 149.3 cm, and 111.9 cm.

What are they saying here exactly? That CryoSat2 data so far has overestimated average ice thickness by over 1 m?

I think not quite: To me 'difference' is an always positive quantity not a vector which has direction. So if 52% of time CS2 is over 1m thicker than reality and 48% of time it is over 1m thinner than reality then the mean difference is over 1m however in this case the volume only has to be adjusted by 4% of area * over 1m thickness difference. That is a lot less than Neven is suggesting.
Title: Re: Piomas vs. CryoSat
Post by: jdallen on January 27, 2014, 03:56:34 AM
What are they saying here exactly? That CryoSat2 data so far has overestimated average ice thickness by over 1 m?
I think not quite: To me 'difference' is an always positive quantity not a vector which has direction. So if 52% of time CS2 is over 1m thicker than reality and 48% of time it is over 1m thinner than reality then the mean difference is over 1m however in this case the volume only has to be adjusted by 4% of area * over 1m thickness difference. That is a lot less than Neven is suggesting.
As you say, crandles.  The wag in me though, judging from the ELTF variability, want's to chime in to suggest that in many cases/areas, the best that could be said of the ELTF data is, "there is ice here" vs "there is thicker ice here".  It makes the spot data provided by buoys valuable for adjusting thickness estimates. 

I will be very interested to see how the new methodology changes our understanding of the pack's 'topography'.

It strikes me... is there a chance they may be able to run the new algorithm against previous data?  That could be revealing as well!
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on January 27, 2014, 08:00:33 AM

I think not quite: To me 'difference' is an always positive quantity not a vector which has direction. So if 52% of time CS2 is over 1m thicker than reality and 48% of time it is over 1m thinner than reality then the mean difference is over 1m however in this case the volume only has to be adjusted by 4% of area * over 1m thickness difference. That is a lot less than Neven is suggesting.

Apart from positive quantities and vectors there are some curious things, sometimes called "negative quantities".


And no, "difference" is not open to interpretation:

(...) mean freeboard differences (CryoSat-2 – IceBridge) of (...)


When IceBridge is larger, the difference will be negative.

Your intepretation would be a ver strange one, seldom used in science. Usually they use someting like RMS, it used al the time in the Laxon et al. paper.

If still in doubt, just look at the graphs in this paper.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on January 27, 2014, 08:36:02 AM
Attached is fig 12, freeboard differences. Multiply by 9 to get proximate thickness diffs.

Title: Re: Piomas vs. CryoSat
Post by: crandles on January 27, 2014, 12:32:50 PM
no, "difference" is not open to interpretation:

(...) mean freeboard differences (CryoSat-2 – IceBridge) of (...)


Yes you are right, sorry about that. Comparing Fig 9 and 11 the freeboard tracker similar to Laxon et el is giving larger thicknesses everywhere.


There are considerable areas with freeboard of near 0.5m in March 2011 and 2012 (but not 2013??) (Fig 11) which translates to 4.5m thick ice. However Chris Reynolds has shown there isn't much ice over 2m thick in PIOMAS after 2010:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Ffarm8.staticflickr.com%2F7361%2F11495454335_7a2cfa0b67_o.png&hash=9f8841e5c89baf60ee607db6487d7e93)

Laxon et al show cryosat2 volume of about 16K Km^3 versus piomas 14K Km^3

Does this suggest that the bias correction (or other differences) done in Laxon et al (but not in the freeboard tracker in this Kurtz et al paper) is rather large? Does this make the differences quoted by the waveform method is paper seem small when compared to the large differences?

Should the waveform method differences be compared to Laxon et al uncertainties? Or does it require something more sophisticated like use half the icebridge data to apply bias corrections to Laxon et al method and Kurtz et al waveform method then see which does best compared to the other half of the icebridge data?

Or is the paper doing a fair comparison, 'before bias correction' against 'before bias correction'?
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on January 27, 2014, 01:36:20 PM
As I read it, they carefully suggest that the previous results were effectively biased by selection of ice density and snow thickness:

The focus of this study is to develop a new method for the retrieval of sea ice free
board from CryoSat-2 data. We demonstrate that this method is consistent with inde-
pendent measurements from airborne laser and radar altimetry data sets from NASA’s
Operation IceBridge mission to retrieve sea ice thickness which eliminates the need to
utilize different ice density and snow depth values as an effective bias correction.

I have quoted the snow somewhere before. About ice density:

These quantities are due to environmental processes and should be applied in a con-
sistent manner in the retrieval of sea ice thickness regardless of which instrument is
used. In the case of sea ice density, previous studies have utilized a wide range of
values, which will result in large differences between data sets if the same physical
assumptions are used. For example, in the study by Kwok et al. (2009) an ice-density
of 925 kgm−3 was used, Kurtz et al. (2011) used a value of 915 kgm−3, while Laxon
et al. (2013) used an estimate of 917 kgm−3 for first year ice and 882 kgm−3 for mul-
tiyear ice. In these studies, the range of sea ice density values for multiyear ice is
particularly large at 43 kgm−3. For a typical multiyear sea ice floe with 60 cm of snow-
ice freeboard and 35 cm of snow depth, the sea ice thickness estimate differs by 1.1 m
within this range of ice densities.

Yet the results of these studies agree quite well despite these large differences in density. This leads logically to the freeboard measurements:

Despite the large-scale mean agreement of the sea
ice thickness data sets described in previous studies, this discrepancy in physical as-
sumptions points to the source of the differences as being due to potential biases in
the freeboard and snow depth data sets used. This large discrepancy underscores the
need to establish a set of consistent physical constants for use in the retrieval of sea
ice thickness from satellite radar and laser altimetry data
Title: Re: Piomas vs. CryoSat
Post by: crandles on January 27, 2014, 02:03:57 PM
Laxon et al:
Nevertheless, comparison of CS-2 measurements with three independent in situ data sets reveals differences of less than 0.1 m in thickness when averaged on a large scale, or over a full winter growth season.

Kurtz et al:
the mean sea ice thickness differences were 20.6 cm, 23.3 cm, and 10.6 cm.
...
A bias of 1.9 cm was found in the waveform fitting method freeboard retrievals compared to the IceBridge data, this bias is consistent with the estimated range bias due to off-nadir ranging of lead points shown by Armitage and Davidson (2014).

How to compare? Is it
20.6-1.9*9=  3.5cm
23.3-1.9*9=  6.2cm
10.6-1.9*9= -6.5cm

These are all <0.1m so the errors are of similar magnitude?



Title: Re: Piomas vs. CryoSat
Post by: crandles on January 27, 2014, 02:31:09 PM
For example, in the study by Kwok et al. (2009) an ice-density
of 925 kgm−3 was used, Kurtz et al. (2011) used a value of 915 kgm−3, while Laxon
et al. (2013) used an estimate of 917 kgm−3 for first year ice and 882 kgm−3 for mul-
tiyear ice. In these studies, the range of sea ice density values for multiyear ice is
particularly large at 43 kgm−3. For a typical multiyear sea ice floe with 60 cm of snow-
ice freeboard and 35 cm of snow depth, the sea ice thickness estimate differs by 1.1 m
within this range of ice densities.

Yet the results of these studies agree quite well despite these large differences in density. This leads logically to the freeboard measurements:

Despite the large-scale mean agreement of the sea
ice thickness data sets described in previous studies, this discrepancy in physical as-
sumptions points to the source of the differences as being due to potential biases in
the freeboard and snow depth data sets used. This large discrepancy underscores the
need to establish a set of consistent physical constants for use in the retrieval of sea
ice thickness from satellite radar and laser altimetry data

If Laxon et al get difference of <0.1m then couldn't an alternative explanation be that as ice gets thinner while snow remains similar (possibly increases slightly) the density that should be used changes over time such that 925kgm-3 is a sensible value for 2009, 915 sensible for 2011, while in 2013 a more sophisticated 917 / 882 split for FYI / MYI is sensible.

With a large change of 1.1m in ice thicknesses possible then I can see that this effectively is a bias correction for Laxon et al method. If ice to snow thickness ratio is changing then requiring the same density to be used does not seem sensible, if I have understood correctly. IOW, the set of consistent physical constants that needs to be established may need to change over time.

I am still left feeling I don't know if the method is an improvement or not.

It seems that Cryosat2 volume is likely to be fairly similar to what has been previously reported (not 1m thinner).
Title: Re: Piomas vs. CryoSat
Post by: crandles on January 27, 2014, 04:40:46 PM
Would a comment on the paper something like the following be sensible?

Laxon et al 2013 find "comparison of CS-2 measurements with three independent in situ data sets reveals differences of less than 0.1 m in thickness when averaged on a large scale, or over a full winter growth season". Comparison with this needs to be much more prominent than with your empirical lead and threshold tracker (ELTF), which you have found to be badly wrong.

In the introduction you assert
"Differences in sea ice thickness estimates from altimetry data arise in particular to the use of different density values and snow depth estimates which are used in the retrieval of sea ice thickness. These quantities are due to environmental processes and should be applied in a consistent manner in the retrieval of sea ice thickness regardless of which instrument is
used. In the case of sea ice density, previous studies have utilized a wide range of
values, which will result in large differences between data sets if the same physical assumptions are used. For example, in the study by Kwok et al. (2009) an ice-density
of 925 kgm−3 was used, Kurtz et al. (2011) used a value of 915 kgm−3, while Laxon
et al. (2013) used an estimate of 917 kgm−3 for first year ice and 882 kgm−3 for multiyear
ice. In these studies, the range of sea ice density values for multiyear ice is
particularly large at 43 kgm−3 5 . For a typical multiyear sea ice floe with 60 cm of snowice
freeboard and 35 cm of snow depth, the sea ice thickness estimate differs by 1.1m
within this range of ice densities. Despite the large-scale mean agreement of the sea
ice thickness data sets described in previous studies, this discrepancy in physical assumptions
points to the source of the differences as being due to potential biases in the freeboard and snow depth data sets used. This large discrepancy underscores the need to establish a set of consistent physical constants for use in the retrieval of sea ice thickness from satellite radar and laser altimetry data."

and your method "eliminates the need to utilize different ice density and snow depth values as an effective bias correction."

Pointing out that different assumptions is an effective bias correction and that you would prefer to eliminate this is sensible. However I wonder if the paper would be improved by considering whether the density assumption needs to change with the year. Presumably as ice is getting thinner it may be correct for the density value to be declining with time. Would adding that considering whether the density assumptions can be varied over time as a function of PIOMAS values be a sensible piece of suggested additional work?

I suggest the implications of the paper need more discussion. As it appears the errors you find are only as low as Laxon et al 2013 if you apply a bias correction to your method, it doesn't seem clear whether the method is an improvement or not. Does your method imply higher or lower Arctic sea ice volume than reported in Laxon et al? If the errors are similar what scope is there for improved estimate of sea ice volume using a combination of both methods (presumably you would want to give more weight to your method for areas that are a long way from a lead)?


Title: Re: Piomas vs. CryoSat
Post by: Wipneus on January 27, 2014, 05:49:43 PM

If Laxon et al get difference of <0.1m then couldn't an alternative explanation be that as ice gets thinner while snow remains similar (possibly increases slightly) the density that should be used changes over time such that 925kgm-3 is a sensible value for 2009, 915 sensible for 2011, while in 2013 a more sophisticated 917 / 882 split for FYI / MYI is sensible.

Snow is a big problem. It was already discussed in this thread. I speculate it is also the main reason why there has been no Cryosat-2 data reported yet for the Antarctic (where snow is often thicker than the ice).

I am still left feeling I don't know if the method is an improvement or not.

It seems that Cryosat2 volume is likely to be fairly similar to what has been previously reported (not 1m thinner).

Even if no better data on thickness and volume come out of it, the advantages of getting the freeboard right are huge:
- better constraints on snow;
- better constraints on ice densities;

These have important impacts on ice forming and melting and as such will improve the modelling. In other words helps us to understand better what is going on.

Think of it, density depends mostly on the salt contents (brine inclusion). That influences the melting point, the mechanical properties but also the porosity of ice: forming and draining of melt pools.

Further Cryosat-2 data is seen as a vindication of PIOMAS. That may not be as strong as it looked if this paper has it right.
 
These guys with their new method have already identified a slight misalignment of the satellite (nadir is not exactly nadir). Even looks like this is worthy stuff.

Would a comment on the paper something like the following be sensible?
Commenting is open until 21st of March, there is some time.
I think from science pov, these guys have covered the issues. Yet a clarification that the big 1.5m
improvement does not translate into similar Cryosat's new estimate seems in order (to avoid misunderstandings). 
Title: Re: Piomas vs. CryoSat
Post by: crandles on January 27, 2014, 06:22:07 PM
Yes probably want to scratch most of that suggested comment because I wasn't thinking straight and almost certainly I still don't understand enough about it.

Yes even if the method isn't better, it is good that the work has been done: It may not be better for one type of task but it may be better for another. It is just that the title of the paper is 'an improved ..." and without comparing to the less than 0.1 m in Laxon et al, do we know whether it is improved or not?

Further Cryosat-2 data is seen as a vindication of PIOMAS. That may not be as strong as it looked if this paper has it right.

With the errors looking to be of similar magnitude, AFAICS the vindication might be slightly worse or slightly better. If you see reason to think it will be worse rather than better then please explain.

the advantages of getting the freeboard right are huge

Sure, but do we think the freeboard is more correct than Laxon et al?
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on January 27, 2014, 06:59:46 PM

Further Cryosat-2 data is seen as a vindication of PIOMAS. That may not be as strong as it looked if this paper has it right.

With the errors looking to be of similar magnitude, AFAICS the vindication might be slightly worse or slightly better. If you see reason to think it will be worse rather than better then please explain.
If I had know that the Cryosat-2 data includes a bias of about 1.5m, then I would have been less impressed. That is all I wanted to say.
the advantages of getting the freeboard right are huge

Sure, but do we think the freeboard is more correct than Laxon et al?
It is what this paper is claiming  (with the assumption that IceBridge is correct).
Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on January 27, 2014, 08:43:53 PM
I've not read much on IceBridge, but when I was looking at the raw data with a view to intercomparison with PIOMAS I was stunned at the uncertainties stated with each reading. IIRC they were often as large as the stated thickness.
Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on April 30, 2014, 08:31:04 PM
A new paper has just been published in The Cryosphere, entitled "Uncertainties in Arctic sea ice thickness and volume: new estimates and implications for trends"

http://www.the-cryosphere.net/8/705/2014/tc-8-705-2014.html (http://www.the-cryosphere.net/8/705/2014/tc-8-705-2014.html)

16 pages of interesting stuff, including discussion about the uncertainties in ice density and snow depth.

The ultimate conclusion:

Our results still reveal a decline in sea ice volume between the ICESat (2003–2008) and CryoSat-2 (2010–2012) periods, but less dramatic than reported in previous studies. However, final quantitative conclusions about a change in sea ice volume are hard to make, considering the large uncertainties and unresolved biases found in our study.
Title: Re: Piomas vs. CryoSat
Post by: ChasingIce on May 01, 2014, 12:52:29 AM
So decline over the last 33 years is probably more than the 75% to 80% reduction in minimum volume since 1979 (16.855 down to 3.261 K Km^3).
Right Chris, that would be an 80.7% decline Dr. Schweiger refers to. But he goes on to say that the newly published data makes that 80% decline look too conservative. I still don't see that.
Anyone?

Yes, you go from 1979 maximum to 2012 minimum to come up with the ~80%
Title: Re: Piomas vs. CryoSat
Post by: ktonine on May 01, 2014, 05:39:29 AM
Yes, you go from 1979 maximum to 2012 minimum to come up with the ~80%

1979 MIN 16.855   2012 MIN 3.673   % Change 78.21
1979 MAX 33.035   2012 MIN 3.673   % Change 88.88

It's minimum to minimum that they're comparing.  It would be rather meaningless to compare maximum to minimum.


Title: Re: Piomas vs. CryoSat
Post by: crandles on May 01, 2014, 03:43:02 PM
A new paper has just been published in The Cryosphere, entitled "Uncertainties in Arctic sea ice thickness and volume: new estimates and implications for trends"

http://www.the-cryosphere.net/8/705/2014/tc-8-705-2014.html (http://www.the-cryosphere.net/8/705/2014/tc-8-705-2014.html)

16 pages of interesting stuff, including discussion about the uncertainties in ice density and snow depth.

The ultimate conclusion:

Our results still reveal a decline in sea ice volume between the ICESat (2003–2008) and CryoSat-2 (2010–2012) periods, but less dramatic than reported in previous studies. However, final quantitative conclusions about a change in sea ice volume are hard to make, considering the large uncertainties and unresolved biases found in our study.

In case anyone has difficulty getting pas thalf way in the abstract where it says

The mean total sea ice volume is 10120±1280 km3 in October/November and 13250±1860 km3 in February/March for the time period 2005–2007.

There is a restricted area of study shown by fig 1: it is cut off at Bering Strait, Severnaya Zemlya to Franz Josef to Svalbard to NE Greenland. Also Canadian Archipelago, Baffin Bay... are excluded.

10120 is near PIOMAS values (2005: 10.209 12.892 2006: 9.838 12.303 2007: 7.135 10.472 average 10.475). After deducting remaining ice in Canadian Archipelago and Greenland sea, IceSat is probably a little higher than PIOMAS.

Feb March 2007 per PIOMAS of 20.863 23.031 and higher in 2005 and 2006 obviously cannot be compared with 13250 without deducting lots of volume from PIOMAS figures for the excluded areas.

.

The difference between 10120 and 13250 seems small, but given other comparisons of ICESat to PIOMAS, perhaps PIOMAS difference is even smaller for this limited region.
Title: Re: Piomas vs. CryoSat
Post by: crandles on April 17, 2015, 03:36:10 PM
This February, Cryosat saw average sea-ice floe thicknesses of just over 1.7m, giving a volume across the Arctic of nearly 24,000 cubic km. Back in the winter of 2013, following strong melting during the previous summer, floe thicknesses averaged 1.5m and the volume fell below 21,000 cu km.
http://www.bbc.co.uk/news/science-environment-32348291 (http://www.bbc.co.uk/news/science-environment-32348291)

PIOMAS has

2015  32  20.348
2015  60  22.524
avg 21.502

2013 avg Feb 19.376
so Cryosat continues to have more volume in winter.
Title: Re: Piomas vs. CryoSat
Post by: crandles on April 17, 2015, 03:48:36 PM
And to mark the spacecraft's fifth birthday in orbit, the team is switching on a new, near-real-time service to aid science and maritime activities.

Sea Ice thickness products from CryoSat NRT (near real time) released. These include 2, 14, and 28-day Arctic maps and thickness timeseries from Oct-2010 until the latest available Cryosat NRT products.

Monthly thickness and volume maps from the archive (2010-2015) will be released in the next few months.

http://www.cpom.ucl.ac.uk/csopr/index.html (http://www.cpom.ucl.ac.uk/csopr/index.html)
http://www.cpom.ucl.ac.uk/csopr/seaice.html (http://www.cpom.ucl.ac.uk/csopr/seaice.html)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.cpom.ucl.ac.uk%2Fcsopr%2Fsidata%2Fthk_28.png&hash=f2d0199709d1124a821000ec1f466d41)
Title: Re: Piomas vs. CryoSat
Post by: Siffy on April 17, 2015, 04:11:54 PM
And to mark the spacecraft's fifth birthday in orbit, the team is switching on a new, near-real-time service to aid science and maritime activities.

Sea Ice thickness products from CryoSat NRT (near real time) released. These include 2, 14, and 28-day Arctic maps and thickness timeseries from Oct-2010 until the latest available Cryosat NRT products.

Monthly thickness and volume maps from the archive (2010-2015) will be released in the next few months.

http://www.cpom.ucl.ac.uk/csopr/index.html (http://www.cpom.ucl.ac.uk/csopr/index.html)
http://www.cpom.ucl.ac.uk/csopr/seaice.html (http://www.cpom.ucl.ac.uk/csopr/seaice.html)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.cpom.ucl.ac.uk%2Fcsopr%2Fsidata%2Fthk_28.png&hash=f2d0199709d1124a821000ec1f466d41)

Odd how the ice in the Barrents is a metre thick even on the ice edge, you'd expect or at least I expected some kind of tapering off of ice thickness.
Title: Re: Piomas vs. CryoSat
Post by: crandles on April 17, 2015, 05:48:21 PM

Odd how the ice in the Barrents is a metre thick even on the ice edge, you'd expect or at least I expected some kind of tapering off of ice thickness.

I am suspecting that some areas shown as white are too thin to reliably measure as well as possibly also being no measurements or no ice. Even so, there is a lot of green and little blue in Southern Baffin Bay as well.
Title: Re: Piomas vs. CryoSat
Post by: Neven on April 17, 2015, 06:25:41 PM
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.cpom.ucl.ac.uk%2Fcsopr%2Fsidata%2Fthk_28.png&hash=f2d0199709d1124a821000ec1f466d41)

Compared to SMOS:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fforum.arctic-sea-ice.net%2Findex.php%3Faction%3Ddlattach%3Btopic%3D587.0%3Battach%3D15611%3Bimage&hash=f9e3ecc7f7bc501d104eacad8e128784)
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on April 17, 2015, 07:16:21 PM
Just posting this here, not completely on-topic but I might add Cryosat later.

This is AMSR2 volume, compared with PIOMAS, calculated from the ice thickness maps in the ADS Sea Ice monitor. Inverting the colorscale for thickness and calculating the area of each pixel (for a 10 km polar stereo graphic projection)  volume can be calculated.

I am ignoring:
-pole hole
-fraction of melting ice
-difference between PIOMAS domain and AMSR2 domain (I am using all the ice in the image).

There is a warning that the AMSR2 thickness is not reliable during the melting season, but at least we can say that the results are not all that crazy.



Title: Re: Piomas vs. CryoSat
Post by: ghoti on April 17, 2015, 07:18:27 PM

Odd how the ice in the Barrents is a metre thick even on the ice edge, you'd expect or at least I expected some kind of tapering off of ice thickness.

If you go to the map page and click on a spot you get a more zoomed in map and a chart of the data for the specific point you clicked. When you do this it looks like you get a much larger range of thicknesses. I guess the overview map is "averaging" the colours and thicknesses. The 1 meter thick ice along the edge of the Barents is shown as being between 0.5m and 1.5m.

Title: Re: Piomas vs. CryoSat
Post by: DavidR on April 18, 2015, 12:19:34 AM

Odd how the ice in the Barrents is a metre thick even on the ice edge, you'd expect or at least I expected some kind of tapering off of ice thickness.

I am suspecting that some areas shown as white are too thin to reliably measure as well as possibly also being no measurements or no ice. Even so, there is a lot of green and little blue in Southern Baffin Bay as well.

If you check the closeups or the shorter time frames you can see that the image is built from a series of single passes providing  information covering a very narrow band, so anywhere not coloured can be assumed to be not measured unless it is outside the expected area of ice.

Looking at the distribution of the ice, does make me wonder if the isolated pockets of thick ice have the same resistance to melting as the solid area of thick ice above Ellesmere island. I assume not. 

Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on April 18, 2015, 11:01:30 AM
An extract from the data manual that may be relevant?

Sea Ice near real time thickness products are currently available in ASCII and netCDF formats in either a whole Arctic 5km resolution or as individual sectors at 1km resolution.

For 5km resolution data, a circular operator of radius 25km is applied when gridding the data and all points receive equal weight.For the 5km grids, only grid points with sea ice thickness data are included in the file (ie it is a sparse grid).

For the 1km grid all grid points north of 60N are present.For 1km resolution data, a circular operator of radius 5km is applied when gridding the data and all points receive equal weight. For the 1km grid all grid points north of 60N are present.

Here's one of the sector maps:

Title: Re: Piomas vs. CryoSat
Post by: slow wing on April 18, 2015, 12:58:30 PM
Thanks to CryoSat for this new offering. Really interesting!
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on April 18, 2015, 06:32:31 PM
Here is PIOMAS, AMSR2-SIT and CRYOSAT compared.

[EDIT: fixed a bug in the AMSR2 volume calculation, the volume is noticeable smaller]

Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on May 05, 2015, 10:08:35 PM
I've just finished (virtually) attending the Sea Ice Prediction Network webinar on "Observations of Arctic Snow and Sea Ice Thickness from Satellite and Airborne Surveys". It seems a recording of the webinar will be made available shortly, but in the meantime the slides can be downloaded from:

http://www.arcus.org/files/SIPN_5May_Webinar_PreliminarySlides_kurtz_1May15_opt.pdf (http://www.arcus.org/files/SIPN_5May_Webinar_PreliminarySlides_kurtz_1May15_opt.pdf)

Here's a very brief overview. Nathan Kurtz from NASA said that IceBridge and CryoSat-2 quick look data will be available from NSIDC "next week". Snow depth will look a lot like the image below.

Slide 18 reveals that PIOMAS does benefit from assimilation of "observed" thickness information when used for the purposes of forecasting, and it seems "weather" reanalysis from MERRA (http://gmao.gsfc.nasa.gov/merra/) can help also.

Slide 17 says that a "near real time CryoSat-2 sea ice thickness product [is] expected in Fall 2015", so I asked the obvious question. It will differ from the CPOM version by using "waveform fitting" (see slides 12-13) instead of "threshold tracking", and "dynamic" climatology (particularly for snow depth) rather than "static". It seems that getting a handle on sea ice density is currently a bigger problem that snow density.

Some papers that were mentioned:

"Seasonal forecasts of Arctic sea ice initialized with observations of ice thickness", Lindsay et al. 2012: http://onlinelibrary.wiley.com/doi/10.1029/2012GL053576/full (http://onlinelibrary.wiley.com/doi/10.1029/2012GL053576/full)

"Interdecadal changes in snow depth on Arctic sea ice", Webster et al. 2014: http://onlinelibrary.wiley.com/doi/10.1002/2014JC009985/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014JC009985/abstract)

"Using the interferometric capabilities of the ESA CryoSat-2 mission to improve the accuracy of sea ice freeboard retrievals", Armitage and Davidson 2014: http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6479282 (http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6479282)

"An improved CryoSat-2 sea ice freeboard retrieval algorithm through the use of waveform fitting", Kurtz et al. 2014: http://www.the-cryosphere.net/8/1217/2014/ (http://www.the-cryosphere.net/8/1217/2014/)
Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on May 08, 2015, 05:21:33 PM
Here's the recent SIPN IceBridge/CryoSat webinar:

http://youtu.be/CYnb_JRMK84 (http://youtu.be/CYnb_JRMK84)

My "obvious question" is asked at 43:25 or thereabouts.
Title: Re: Piomas vs. CryoSat
Post by: Steven on July 20, 2015, 08:33:01 PM
New paper by Tilling et al. about the 2010-2014 CryoSat measurements:

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2489.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2489.html)


Clicking on this link (http://www.nature.com/articles/ngeo2489.epdf?referrer_access_token=hEF2D-iTlepwbstDKmPi9NRgN0jAjWel9jnR3ZoTv0MtRSPtH79Viu1xFYAYx0s4cUyVZ_oPSqf2s0pBBYKx97kwOOEjSUci7As0RQyRbHZqoH3QtKXysbD7FZnEGW1vv6xiZhfPrcYLQVHojc21xsz2bWEyVsWVkxTwDGjDJaD0CQb8KwFWX-pSFdG5-zTXuYOxrCOO4CmGca1kzn50GxAeFX_QP6qz9mppBfYw-_Q3W2a2mfRSn9XleKPPr3we&tracking_referrer=www.theguardian.com) should directly open the pdf-file of the paper (but this may not work for some browsers).  Supplementary information of the paper is here (http://www.nature.com/ngeo/journal/vaop/ncurrent/extref/ngeo2489-s1.pdf).


See also this blog post on Carbon Brief:

http://www.carbonbrief.org/blog/2015/07/cool-arctic-summer-brought-brief-recovery-in-2013-sea-ice-loss (http://www.carbonbrief.org/blog/2015/07/cool-arctic-summer-brought-brief-recovery-in-2013-sea-ice-loss)

Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on July 20, 2015, 09:16:50 PM
See also this blog post on Carbon Brief

I've already pointed them back in this direction!
Title: Re: Piomas vs. CryoSat
Post by: plinius on July 21, 2015, 12:51:19 AM
one thing to assess uncertainties and biases would be to have ex post corrections for PIOMAS pubished. The model will produce wrong dates for the appearance/disappearance of ice, which can be used to infer the model bias. Published anywhere?

Title: Re: Piomas vs. CryoSat
Post by: ChrisReynolds on July 21, 2015, 06:14:58 PM
Not as far as I know Plinius.
Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on July 21, 2015, 11:20:47 PM
Rachel Tilling suggested I was confused between CryoSat-2 and IceBridge.

http://www.carbonbrief.org/blog/2015/07/cool-arctic-summer-brought-brief-recovery-in-2013-sea-ice-loss#comment-2148344790 (http://www.carbonbrief.org/blog/2015/07/cool-arctic-summer-brought-brief-recovery-in-2013-sea-ice-loss#comment-2148344790)

In actual fact I don't think I am. I get the distinct impression that UCL isn't up to speed on what NASA have been up to recently.
Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on July 22, 2015, 06:56:47 PM
Following a frank exchange of views on Carbon Brief Rachel points out that:

We have now released our spring and autumn thickness data for the whole CryoSat-2 period on our website:

http://www.cpom.ucl.ac.uk/csopr/seaice.html?thk_period=0&select_thk_vol=select_thk&season=Autumn&ts_area_or_point=all&basin_selected=0&show_cell_thickness=0 (http://www.cpom.ucl.ac.uk/csopr/seaice.html?thk_period=0&select_thk_vol=select_thk&season=Autumn&ts_area_or_point=all&basin_selected=0&show_cell_thickness=0)

This is the data that is presented in the paper, and has now been peer reviewed. Thanks all for your interest.

This is the "Final" data, not "Quick look".

See also all the usual BS from the usual suspects about this paper amongst others

http://forum.arctic-sea-ice.net/index.php/topic,578.msg57562.html#msg57562 (http://forum.arctic-sea-ice.net/index.php/topic,578.msg57562.html#msg57562)

I got a "like" from Ed Hawkins on Twitter :)
Title: Re: Piomas vs. CryoSat
Post by: shendric on July 23, 2015, 12:12:51 AM
See my comment in Carbon Brief.
http://www.carbonbrief.org/blog/2015/07/cool-arctic-summer-brought-brief-recovery-in-2013-sea-ice-loss#comment-2148344790 (http://www.carbonbrief.org/blog/2015/07/cool-arctic-summer-brought-brief-recovery-in-2013-sea-ice-loss#comment-2148344790)

There are other papers on the 2013/2014 winter season as seen by CryoSat and the conclusions are not necessarily the same.

http://rsta.royalsocietypublishing.org/content/373/2045/20140157 (http://rsta.royalsocietypublishing.org/content/373/2045/20140157)
http://onlinelibrary.wiley.com/doi/10.1002/2015GL064081/full#grl53020-bib-0003%29 (http://onlinelibrary.wiley.com/doi/10.1002/2015GL064081/full#grl53020-bib-0003%29)

Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on July 23, 2015, 06:21:56 PM
See my comment in Carbon Brief.

Welcome Stefan!

See also my subsequent comment over at Carbon Brief.

Thanks once again for the heads up.
Title: Re: Piomas vs. CryoSat
Post by: Wipneus on September 07, 2015, 10:45:58 AM
Occasionally I visit the Cryosat site, to see whether new thickness/volume data for the year 2015 has been added. We are still missing volume data for March and April and the new measuring season is due to start this month.

What can be noticed is that the volume data for December (2014) and January seem to have been downgraded from precise to near real time, adding some uncertainty to the latest calculated volume data from Cryosat.

Title: Re: Piomas vs. CryoSat
Post by: plinius on October 24, 2015, 01:26:33 PM
Cryosat measurements for the arctic are back online since 23nd of October.
http://www.cpom.ucl.ac.uk/csopr/seaice.html (http://www.cpom.ucl.ac.uk/csopr/seaice.html)
Not sure how reliable that is, but if their 28-day averages are true, there would be nearly no thick ice left in front of the Canadian Archipelago, and pretty few in the central basin.
Title: Re: Piomas vs. CryoSat
Post by: Steven on October 26, 2015, 12:30:57 PM
Cryosat tracks Arctic sea ice freeze-up
http://www.bbc.com/news/science-environment-34619291 (http://www.bbc.com/news/science-environment-34619291)


Arctic sea-ice volume during the first two weeks of October was about 6,200 cubic km.

The number comes from Europe's Cryosat mission, which has just restarted its near-real-time data service.
...

Volume of Arctic autumn sea ice: First two weeks of October (average):

2010: 5,900 cubic km;
2011: 4,500 cu km;
2012: 4,600 cu km;
2013: 7,800 cu km;
2014: 6,800 cu km;
2015: 6,200 cu km
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on October 28, 2015, 07:55:12 PM
Icesat+Cryosat-2   vs. PIOMAS

(warning: it's just my own rough estimate)

(https://diablobanquisa.files.wordpress.com/2015/10/imagen17.png)



Kwok and Cunningham 2015 (http://rsta.royalsocietypublishing.org/content/373/2045/20140157)
CPOM (http://www.bbc.com/news/science-environment-34619291)
PIOMAS (http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/)


Title: Re: Piomas vs. CryoSat
Post by: Steven on April 07, 2016, 08:33:42 PM
Interesting article today at Carbon Brief:

http://www.carbonbrief.org/analysis-the-highly-unusual-behaviour-of-arctic-sea-ice-in-2016 (http://www.carbonbrief.org/analysis-the-highly-unusual-behaviour-of-arctic-sea-ice-in-2016)

The latest observations of sea ice thickness from the CryoSat satellite show that the ice was, on average, 1.8m thick in March [2016], says [Andrew] Shepherd. This is about 10cm thinner than the same time last year, but about 10cm thicker than the record winter low in 2013.

Shepherd and his team will use measurements of thickness together with sea ice extent to estimate the volume of ice left at the end of winter. These results aren’t public yet, but Shepherd tells Carbon Brief it’s not looking hopeful:

“If things continue as in previous years, I suspect this year could see a tie with that record low for volume as well, but it’s too early to say for sure.”
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on October 19, 2016, 01:30:45 AM
2015, 26 Sep-23 Oct
(https://diablobanquisa.files.wordpress.com/2015/10/thk_28_big.png)


2016, 18 Sep-15 Oct
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimages.meteociel.fr%2Fim%2F6957%2Fthk_28_uis8.png&hash=b79ff5b04eefae552aff430a916e9424)






Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on November 24, 2016, 12:30:53 AM
CS2, Oct-Nov 2011-2016 (click for a larger version):

(https://diablobanquisa.files.wordpress.com/2016/11/111.png) (https://diablobanquisa.files.wordpress.com/2016/11/111.png)

http://www.esa.int/Our_Activities/Observing_the_Earth/Space_for_our_climate/Ice_matters (http://www.esa.int/Our_Activities/Observing_the_Earth/Space_for_our_climate/Ice_matters)

http://www.cpom.ucl.ac.uk/csopr/seaice.html (http://www.cpom.ucl.ac.uk/csopr/seaice.html)



Title: Re: Piomas vs. CryoSat
Post by: slow wing on November 24, 2016, 02:21:02 AM
Thanks diablobanquisa, that's very interesting.

Presumably they are all 28-day Thickness maps collecting measurements over 24/10 - 20/11?

So this is precise and well-calibrated for year-to-year comparisons?

It shows almost no ice thicker than 2 m at that time of year in 2011, then 2013 a big recovery year before falling away again.

This year at least has some thicker ice off the Canadian Arctic coastline but the overall extent is of course the lowest.
Title: Re: Piomas vs. CryoSat
Post by: seaicesailor on November 24, 2016, 06:29:41 AM
Yes and at this time of the year Hycom ACNFS does not seem really off the mark wrt Cryosat, or not as much as it looked in previous years.
The various compaction periods since end of August have increased this ice accumulation north of the CAA and Greenland coasts and not much Fram export until recently. This is good for that core of ice, but its extent is rather limited. Most of the CAB and the peripheral ice is dangerously thin and young.
Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on November 24, 2016, 10:12:31 AM
It shows almost no ice thicker than 2 m at that time of year in 2011, then 2013 a big recovery year before falling away again.

You may wish to read the paper mentioned by Stefan Hendricks above:

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064081/full#grl53020-bib-0003%29 (http://onlinelibrary.wiley.com/doi/10.1002/2015GL064081/full#grl53020-bib-0003%29)

We find a positive correlation between buoy snow freeboard and CryoSat-2 freeboard estimates, revealing that early snow accumulation might have caused a bias in CryoSat-2 sea ice thickness in autumn 2013.
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on November 24, 2016, 11:29:14 AM

Presumably they are all 28-day Thickness maps collecting measurements over 24/10 - 20/11?

So this is precise and well-calibrated for year-to-year comparisons?



No, but until the final data for 2015 and 2016 are released by CPOM,  this is the best we have. I think it is reliable enough for the overall picture.


It shows almost no ice thicker than 2 m at that time of year in 2011, then 2013 a big recovery year before falling away again.

You may wish to read the paper mentioned by Stefan Hendricks above:

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064081/full#grl53020-bib-0003%29 (http://onlinelibrary.wiley.com/doi/10.1002/2015GL064081/full#grl53020-bib-0003%29)

We find a positive correlation between buoy snow freeboard and CryoSat-2 freeboard estimates, revealing that early snow accumulation might have caused a bias in CryoSat-2 sea ice thickness in autumn 2013.

However, Ron Kwok thinks the 2013 summer recovery is real, and mainly due to ice dynamics (convergence, compaction): http://onlinelibrary.wiley.com/doi/10.1002/2015GL065462/full (http://onlinelibrary.wiley.com/doi/10.1002/2015GL065462/full)

"In a different analysis, Ricker et al. [2015] considered the higher MYI freeboard in November 2013 compared to March 2013 to be unlikely after the melt season and surmised that higher ice freeboards may be due to retrieval issues. Even though the retrieval issues merit attention, they neglected to consider the potential of ice convergence and deformation (discussed above) in creating such inconsistencies. Broadly, instead of attributing the ice thickness of this region solely to thermodynamics, the results here highlight the role of dynamics as a source of variability in Arctic Ocean ice thickness that should not be discounted when interpreting retrieval results."

(see also Kwok and Cunningham 2015 (http://rsta.royalsocietypublishing.org/content/373/2045/20140157). And Tilling et al. 2015 (http://www.nature.com/ngeo/journal/v8/n8/full/ngeo2489.html), of course)

Cheers

Title: Re: Piomas vs. CryoSat
Post by: ktonine on November 24, 2016, 01:13:21 PM
Comparing the Cryosat thickness map to the extent map at minima (circa first week of September), and then taking into account the temperatures that we've seen since then, it's difficult to believe any new ice has grown to 1m thickness this fall/winter.  The number of Freezing Degree Days for N80 is still only half of what's needed to grow 1m thick ice and temperatures from N70 to N80 (where most of the new ice resides) have been even warmer.

If temperatures were a uniform -10C it would take  4 months to grow 1m thick ice. For the area between N70 and N80 we've barely seen a month with temperatures below -10C. Thermodynamically it simply isn't possible for much new ice to be greater than 0.6m thick right now.
Title: Re: Piomas vs. CryoSat
Post by: magnamentis on November 24, 2016, 05:22:03 PM
Comparing the Cryosat thickness map to the extent map at minima (circa first week of September), and then taking into account the temperatures that we've seen since then, it's difficult to believe any new ice has grown to 1m thickness this fall/winter.  The number of Freezing Degree Days for N80 is still only half of what's needed to grow 1m thick ice and temperatures from N70 to N80 (where most of the new ice resides) have been even warmer.

If temperatures were a uniform -10C it would take  4 months to grow 1m thick ice. For the area between N70 and N80 we've barely seen a month with temperatures below -10C. Thermodynamically it simply isn't possible for much new ice to be greater than 0.6m thick right now.

exactly my thoughts all the time, thickness maps are almost useless because most of the time obviously incorrect, showing 1m ice where is zero and the likes.

i boldly lean out of the window and say that the 2016 data are non-sense and close to impossible. as you say, neither temps nor conditions were the likes to grow that much several meters thick ice or piling it up that much. perhaps they measure the highest tip sticking out and apply it to a certain area.
Title: Re: Piomas vs. CryoSat
Post by: Tigertown on November 24, 2016, 06:01:31 PM
Could be the darkness or fear of going for a cold swim accidentally, but maybe everyone is scared to walk out on the ice enough to get adequate cores so as to re-calibrate.
I mean, you can understand the surviving MYI being thick, but not new ice.
Title: Re: Piomas vs. CryoSat
Post by: SteveMDFP on November 24, 2016, 06:43:52 PM
Could be the darkness or fear of going for a cold swim accidentally, but maybe everyone is scared to walk out on the ice enough to get adequate cores so as to re-calibrate.
I mean, you can understand the surviving MYI being thick, but not new ice.

Well, validating ice thickness is difficult, but you don't have to be on top of the ice to do so.  You can determine ice thickness quite accurately from below, with submarine instruments.  That data IS being collected as we speak, but most of it is secured in the data banks of the US and Russian navies.  Interestingly, the military of both nations have been quite pro-active in efforts to plan for such dramatic changes in their operating environments.  I suspect they may know quite a lot that we're only able to guess at.
Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on November 24, 2016, 06:58:23 PM
Maybe everyone is scared to walk out on the ice enough to get adequate cores so as to re-calibrate.

With good reason! How would you go about manually sampling sea ice thickness Arctic wide on a regular basis? The nearest you'll get to "re-calibration" is comparison with the data acquired by the NASA Operation IceBridge flights. More from Ron Kwok et al.:

http://dx.doi.org/10.3390/rs8090713 (http://dx.doi.org/10.3390/rs8090713)
Title: Re: Piomas vs. CryoSat
Post by: ghoti on November 24, 2016, 10:01:14 PM
Obviously the Arctic is much too vast to sample manually. Plus
don't forget the tragic deaths of Marc Cornelissen and Philip de Roo in 2015. They were on an expedition in the northern Canadian archipelago measuring ice and observing wildlife when they fell through the ice and died.
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on November 24, 2016, 10:08:21 PM
Incidentally, SMOS (click for a larger version):

(https://diablobanquisa.files.wordpress.com/2016/11/20111120_hvnorth_rfi_l1c.png) (https://diablobanquisa.files.wordpress.com/2016/11/20111120_hvnorth_rfi_l1c.png)

http://www.iup.uni-bremen.de:8084/smos/ (http://www.iup.uni-bremen.de:8084/smos/)





Title: Re: Piomas vs. CryoSat
Post by: Tigertown on November 24, 2016, 10:53:42 PM
No longer ago than early 2015 sea ice was being cored. I remember one sample off the coast of Alaska that turned out to be only one meter thick. It was not really something that had to be done Arctic wide. If you know what the exact measurement is in one place and get readings that it is 32% thicker in another place, you can calculate the depth. They measure many things with satellites using this method, not just ice.

That being said, I personally would not want to go out on the ice, especially nowadays. I do not blame anyone else for trying to use safer methods, whether by airplane, submarine, helicopter, or whatever.
Title: Re: Piomas vs. CryoSat
Post by: ktonine on November 25, 2016, 06:47:33 PM
Not sure if there's a good/easy source to view current temps for latitudes other than N80, but Nick Stokes' at moyhu has an applet that let's you select latitude and longitude (https://moyhu.blogspot.com.au/p/latest-ice-and-temperature-data.html) (scroll about halfway down the page for the applet).  The data and X-axis are not aligned properly --- I'll send a complaint to Nick :)

Here's the Pacific sector from N70 to N80:

(https://3.bp.blogspot.com/-V_BCRJhoA5w/WDh0JTf3FKI/AAAAAAAAAM0/P7earNWnZrwaDO3369iJF013c0oRG2NEACLcB/s1600/N70_80_pacific.JPG)

Climatology would indicate about 890 accumulated FDDs to date
2016 appears to be around 400 accumulated FDDs

Using Lebedev new ice thickness reduces from 0.84m to 0.52m
Using Berillo new ice thickness reduces from 0.68m to 0.43m

Neither of these takes into account the actual date of first ice formation, this means they are likely biased high.

It should also be kept in mind that Cryosat has thickness uncertainties > 0.6m. 
Title: Re: Piomas vs. CryoSat
Post by: Archimid on November 25, 2016, 10:17:43 PM
Interesting tool. Played with it for a little bit and attempted to get regional temps. It is not perfect but I like it. Attached are my best fit for the Chukchi, Barents and Kara.


Using Lebedev new ice thickness reduces from 0.84m to 0.52m
Using Berillo new ice thickness reduces from 0.68m to 0.43m

Neither of these takes into account the actual date of first ice formation, this means they are likely biased high.

It would be interesting to calculate FFD's on a regional basis and somehow apply them to the area of the region.
Title: Re: Piomas vs. CryoSat
Post by: Ice Shieldz on November 26, 2016, 02:53:19 AM
Here is a site that provides 1 week and 1 month GFS hindcast 2 meter temp anomaly means.  As well as archives for previous months going back to 2011
http://www.karstenhaustein.com/climate.php (http://www.karstenhaustein.com/climate.php)
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on November 30, 2016, 07:51:41 PM
http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/Arctic_freeze_slows_down (http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/Arctic_freeze_slows_down)

CryoSat volume update. Looks like tied with previous low for November...

Low, but is it better than expected with the current extent numbers and temperature anomalies?

PIOMAS was tying for the lowest last month, will be interesting to see their numbers in a few days.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.esa.int%2Fvar%2Fesa%2Fstorage%2Fimages%2Fesa_multimedia%2Fimages%2F2016%2F11%2F2011_16_november_arctic_sea-ice_thickness%2F16542447-1-eng-GB%2F2011_16_November_Arctic_sea-ice_thickness_node_full_image_2.gif&hash=6008c96935f78809a9f8fdd8713b3cfe)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.esa.int%2Fvar%2Fesa%2Fstorage%2Fimages%2Fesa_multimedia%2Fimages%2F2016%2F11%2F2011_16_november_arctic_sea-ice_volume%2F16543625-1-eng-GB%2F2011_16_November_Arctic_sea-ice_volume_node_full_image_2.png&hash=e83022fc5f4bd99427bd0b83a6e15ac1)

Title: Re: Piomas vs. CryoSat
Post by: seaice.de on December 01, 2016, 07:01:52 PM
CryoSat2 and SMOS give similar trends. SMOS sees the reduced new ice growth this year.

Click image below to start animation!
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on December 11, 2016, 01:34:32 AM
(https://diablobanquisa.files.wordpress.com/2016/12/cs2_vs_piomas_2016_11.png) (https://diablobanquisa.files.wordpress.com/2016/12/cs2_vs_piomas_2016_11.png)

(https://diablobanquisa.files.wordpress.com/2016/12/cs2_vs_piomas_2016_11_anom.png) (https://diablobanquisa.files.wordpress.com/2016/12/cs2_vs_piomas_2016_11_anom.png)

Title: Re: Piomas vs. CryoSat
Post by: Neven on December 11, 2016, 11:30:46 AM
Thanks, Diablo. Very enlightening.
Title: Re: Piomas vs. CryoSat
Post by: epiphyte on December 11, 2016, 06:00:01 PM
Is it even cold enough for cryosat to work right? (Serious question)
Title: Re: Piomas vs. CryoSat
Post by: crandles on December 11, 2016, 08:28:03 PM
Is it even cold enough for cryosat to work right? (Serious question)

This measurement technique works in autumn, winter and spring. In summer, melt ponds prevent us from estimating sea ice thickness

The problem seems to be surface liquid water related rather than temperature related? So storms more of a problem than the temp being as warm as -10C ?
Title: Re: Piomas vs. CryoSat
Post by: epiphyte on December 12, 2016, 04:18:54 AM
Is it even cold enough for cryosat to work right? (Serious question)

This measurement technique works in autumn, winter and spring. In summer, melt ponds prevent us from estimating sea ice thickness

The problem seems to be surface liquid water related rather than temperature related? So storms more of a problem than the temp being as warm as -10C ?

Right... What I should really have asked was, "Is it dry enough [] ?"
Title: Re: Piomas vs. CryoSat
Post by: Michael on February 10, 2017, 09:27:14 PM
The Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) has released it's CryoSat-2 Sea Ice Thickness data for October 2016 to January 2017, so it is now possible to do a proper comparison with the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) and CryoSat-2 reported sea ice thickness.

The Centre for Polar Observation and Modelling (CPOM) also produce sea ice thickness data derived from CryoSat-2 and their NRT 2 day 1km product is used here to create a monthly average.

In order to properly compare PIOMAS with CryoSat-2, each valid data point in the CPOM dataset is mapped onto the PIOMAS grid, and the corresponding value from the PIOMAS daily gridded dataset is used to create a monthly average. The intention being to sample the PIOMAS grid at the same temporal and spatial frequency as the CryoSat-2 satellite samples the Arctic sea ice and create a CryoSat-2 equivalent monthly average from the PIOMAS data.

The PIOMAS and CPOM data are regridded onto the NSIDC EASE-2 25 km grid, as used by for the AWI sea ice thickness product. The AWI colour bar is used for all three sea ice thickness products.

In the process of generating the monthly averages the opportunity is taken to create a monthly average difference between PIOMAS and CPOM sea ice thickness. To create this monthly average each valid CPOM data point that lies in an ocean grid cell on the PIOMAS gird is subtracted from the corresponding PIOMAS data point

In comparing PIOMAS with CryoSat-2 derived Sea Ice Thickness it is worth noting that PIOMAS reports Effective Sea Ice Thickness, while the CryoSat-2 derived products report Average Sea Ice Thickness. To complicate matters even further, the PIOMAS monthly average presented here is in fact Average Effective Sea Ice Thickness.

The CryoSat-2 satellite does not provided complete coverage of the Arctic in a one month period, and so there are blank areas where no data is avalaible.

Data:

http://data.seaiceportal.de/gallery/index_new.php?lang=en_US]
[url]http://data.seaiceportal.de/gallery/index_new.php?lang=en_US (http://[url)[/url]
http://www.cpom.ucl.ac.uk/csopr/seaice.html (http://www.cpom.ucl.ac.uk/csopr/seaice.html)
http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/data/model_grid (http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/data/model_grid)

Comparison of PIOMAS vS. CryoSat-2 for October 2016


Title: Re: Piomas vs. CryoSat
Post by: Michael on February 10, 2017, 09:29:14 PM
Comparison of PIOMAS vS. CryoSat-2 for November 2016
Title: Re: Piomas vs. CryoSat
Post by: Michael on February 10, 2017, 09:30:51 PM
Comparison of PIOMAS vS. CryoSat-2 for December 2016
Title: Re: Piomas vs. CryoSat
Post by: Michael on February 10, 2017, 09:32:41 PM
Comparison of PIOMAS vS. CryoSat-2 for January 2017
Title: Re: Piomas vs. CryoSat
Post by: Neven on February 10, 2017, 10:27:09 PM
Wow, Michael, this is pure genius. Thanks a lot for making these graphs, I mean comparison maps!

I could sure use such a thing for the next PIOMAS update, but I'm sure you depend on data release by either AWI or CPOM. I've asked Dr Marcel Nicolaus several times when the maps on meereisportal.de were going to be updated, but no response so far.

Edit: meereisportal.de has a http://Jan 2017 CryoSat map (http://data.seaiceportal.de/gallery/index_new.php?active-tab1=measurement&ice-type=thickness&satellite=C&region=n&resolution=monthly&minYear=2017&minMonth=1&maxYear=2017&maxMonth=1&showMaps=y&submit2=display&lang=en_US&active-tab2=thickness) as well now.
Title: Re: Piomas vs. CryoSat
Post by: DrTskoul on February 10, 2017, 10:58:53 PM
Yeah, thanks Mike for the comparison!  So that high volume PIOMAS feature has persisted for some time and is different than what Cryostat shows. I wonder what was the genesis of that feature.
Title: Re: Piomas vs. CryoSat
Post by: Neven on February 10, 2017, 11:10:04 PM
Here's a CryoSat animation showing Jan 2016 vs Jan 2017:

(https://lh3.googleusercontent.com/crXXd7ZKOKc1lVt-Ucv6DsIFu4u3NKODqPLA1leysdR-Usz4UHR9qe0Vv2k03bjxzKCsn5dtjgxlGO9KliS9gOZNj8ERMXqRTURtF3KQgnSWPJkSQPanKt42Doflgv97FfaxBR_1r_SbRUhQdOCZhLuoSAgZ5pszsi-wAXhXHMBw4QADVRN_JYbEwq7cfWqXAvcEiatBYO8nWs3mrlWOX_HN1VFhYoBkFHn7NSMFzLU8HJJ0Q8exfX1GjwaoLEGvuWlAnxuF5siv9rXc3sM2QvpS2HyQqRdx1NEZeEkg3Grl6kIJYDfQHgCSJXPzj7uBmn_rSEPC2nyPiwfUaceXE11fZvP1nCHO27CeSd14XweYQHbiv5ywYAhznAOrDBizusBErm8BI3lcnwdXDh0U6k58oKez3Ze3V7RjWdkR_IlO3SqCEK4qqjXCTXjZesDFnNwxO_19oWPiFEpjIJSYLm3j7N8bZHll3bAzQIuovDCQdvQ7908z-llU5ZUIU8a3d5J5JYI236aQP67p2JYhZQ3PNtRYwBvd27bCDCU-CiseB7aLDACGLe5rQ4Tg9fp_bQia6ukMql8ZZNk3qJY__NKOrjIe1zTp4qITlV-48UYxPr0eH4xG=s800-no)

Maybe it's my eyeball, but I would say that CryoSat suggests that the ice is slightly thicker right now than it was last year around this time. Which is weird, given the FDD anomaly, the cloudy weather, the storms, and PIOMAS saying there's a difference of 2374 km3 in volume and 17 cm in average thickness.

Weird...
Title: Re: Piomas vs. CryoSat
Post by: Neven on February 10, 2017, 11:28:08 PM
Here's a comparison of January 2012-2017:

(https://lh3.googleusercontent.com/Li6zRONkip0kZJxI1w0Lx14-SSkC4HGpVtavBlwQ7rTT7-QpoeQ_Bt5U0mpIcmyO1RHVDA7A2Fyp1Mllu412DV9qLhtUVJRTYqxpmQn8zGPxERQ2Eq63tCeSXI2UVcEsFWiPQnxR8gOm84PjkI4ivsuflLp4G8sOomq4_F11oVjHSFj8kMpr0upBqbeVsOSA5GY_g7lLxPh_MFond45D4WxW5PLIMoOr2j2YeXjV5WJjwNyE_5_NMR6WKXEz-F4B9TFfL1kbhBgRm5LS9j7rsXlsCsieBFHlKJiReuAJ4vH0GIxeA84O2OY-L-jwWAYlxWfgQDrfccpi2zz_7HdiWBQm9mcmqQMcRRMhimzDtnZXQHSX9zEBkxIvcEDEsInDc8KrnG3digkxTIAuhuLlULkMzDSmeQBtgjdSrxhUVCjW7QBVH6VEse65oWqTHEHKfp8AGxXfSd-h-qbx_S9HkMZ3e3itNsq3MIs5dfqi7wV0O7pwcTS2MqWtisNY2ZnUo7bd2l_FOimK59q1rM6IFpTPYpiO5MGpIm6ZnnhK3F2T8tbQrTV-qHatfYYkaIFfwIpGgQs6LSdht3dIHfOMN3nSI9wLyKAwL1QwmZYtxJIGnqHqgH4k=w1200-h800-no)

CryoSat-2 clearly has Jan 2012 and 2013 thinner than Jan 2017. But PIOMAS has this:

(https://lh3.googleusercontent.com/vaCYDW_AYFn1nxuvWg4RD9Zuv9UrwCTQDupgM4qa9dfcS-3zRXB4SY2GOFxW6n93OUi1-A2Zl3L6OHqC6xT2V2pnaaTWBcfwYE6Mt5ciQTtvlsQEGn_SWi_wc1zix7Y86A6z-dPriht3nVV9tUnrVZBfbxShd2DX2tm13uDPfgoZk61GFpmeu3uXzqdJaEFDpsUmxChNsqHaXOnKvGSwkvBNvghrJ_SxXU7ZGxNloBbjBuvZbehIxgNcS5ftG9NFtLEE9E3m4u2EOh8BiV8TwLU8VbKNQFLTzqGj9PIMuzo4Yp9qjqzv6UpkzlOLZoAHhH-JM4gfOZo2GWdUjoxuj7NZ-bkInacBk38urbowQNQH6MYBJUCF73z_4DxfMIo8YxhKzb2MibOUxq7HInl4URQfYXKP9KI-UFmvOaBwVuB7q59a_EXc4yPl_fm0RuD4H3fe0AZEJS494QQ_T2bLK13bpk5_PPsHv8YkXrxLKBeBjqJOI0xV0His7kXec2qjfZg3n0v6EqBkFPvUG69YgPZLCgHBZ8uzCU_ddTS6z5MGVxlMG_vyeuV1yML5Yd_n3ARCnaeOsgQq9EXz84uGw1NhVSAeJMf60wUAvckRwfOFrfttAb8d=w241-h199-no)

Difference with 2012 and 2013 at the end of January is 2270 and 1571 km3 respectively. Okay, CryoSat is showing an average, so let's the take the average of the differences with 2017 at Jan 1st and 31st: 2118 and 1193 km3 respectively.
Title: Re: Piomas vs. CryoSat
Post by: DrTskoul on February 11, 2017, 12:13:01 AM
Weird indeed.

I know we have discussed about it before but Wlwhat is Cryosat's skill in distinguishing snow?
Title: Re: Piomas vs. CryoSat
Post by: epiphyte on February 11, 2017, 06:37:44 AM
Here's a CryoSat animation showing Jan 2016 vs Jan 2017:

(https://lh3.googleusercontent.com/crXXd7ZKOKc1lVt-Ucv6DsIFu4u3NKODqPLA1leysdR-Usz4UHR9qe0Vv2k03bjxzKCsn5dtjgxlGO9KliS9gOZNj8ERMXqRTURtF3KQgnSWPJkSQPanKt42Doflgv97FfaxBR_1r_SbRUhQdOCZhLuoSAgZ5pszsi-wAXhXHMBw4QADVRN_JYbEwq7cfWqXAvcEiatBYO8nWs3mrlWOX_HN1VFhYoBkFHn7NSMFzLU8HJJ0Q8exfX1GjwaoLEGvuWlAnxuF5siv9rXc3sM2QvpS2HyQqRdx1NEZeEkg3Grl6kIJYDfQHgCSJXPzj7uBmn_rSEPC2nyPiwfUaceXE11fZvP1nCHO27CeSd14XweYQHbiv5ywYAhznAOrDBizusBErm8BI3lcnwdXDh0U6k58oKez3Ze3V7RjWdkR_IlO3SqCEK4qqjXCTXjZesDFnNwxO_19oWPiFEpjIJSYLm3j7N8bZHll3bAzQIuovDCQdvQ7908z-llU5ZUIU8a3d5J5JYI236aQP67p2JYhZQ3PNtRYwBvd27bCDCU-CiseB7aLDACGLe5rQ4Tg9fp_bQia6ukMql8ZZNk3qJY__NKOrjIe1zTp4qITlV-48UYxPr0eH4xG=s800-no)

Maybe it's my eyeball, but I would say that CryoSat suggests that the ice is slightly thicker right now than it was last year around this time. Which is weird, given the FDD anomaly, the cloudy weather, the storms, and PIOMAS saying there's a difference of 2374 km3 in volume and 17 cm in average thickness.

Weird...

My hand-waving hypothetical explanation of this is as follows:

1. Cryosat 2 is at it's heart a radar altimeter.
2. Space-based SAR (non-military, at least) has a resolution of at best 10s of meters.
3. Thin, soft ice is more frangible than thick, hard ice.
4. Broken-up ice is more mobile than sheet ice.
5. unstable weather causes ice drift to change direction more than the historical high-pressure, temperature-inverted arctic regime.

--> 3,4 and 5 in combination create a low-density ice field with high-granularity variation in surface height above sea-level. (6)
--> 1 and 2 in combination make it impossible for cryosat to distinguish between  (6), above, (which has low density, volume) and solid sheet ice. (which has high density, volume) (7)

... so my SWAG on this is that under this year's conditions (i.e. characterized by 3,4 and 5 above) Cryosat is likely on the high side in many areas. This might be testable if there's a higher-resolution radar than Cryosat (S1A/B?) available for comparison. Areas which show up on the latter as uniformly reflective (i.e. dark or light depending on the angle) should show better Cryosat-PIOMAS correlation than the noisier regions.

Not saying that PIOMAS is right either, mind you :)    (Have been pointedly not saying that since pretty much my first post on this forum!)




Title: Re: Piomas vs. CryoSat
Post by: S.Pansa on February 11, 2017, 08:42:36 AM
... what is Cryosat's skill in distinguishing snow?

I was wondering about that too. The PIOMAS numbers did make a lot of sense to me ...

For what it is worth, below the snow thickness for late January 2012, 2013 and 2017 - according to TOPAZ4.
On the first glance the shape of the  2017 snow cover could partly explain the band of relatively thick ice (~3 m)  from North Greenland to the ESS in Cryosat. But then again, there was more snow in 2012 (and even in 2013). 
If anything, the snow cover could perhaps explain the odd fat bulge near the pole in piomas' estimates for 2017. To sum it up: I have no clue what's going on  8)
 
Title: Re: Piomas vs. CryoSat
Post by: seaicesailor on February 11, 2017, 11:53:49 AM
Here's a comparison of January 2012-2017:

(https://lh3.googleusercontent.com/Li6zRONkip0kZJxI1w0Lx14-SSkC4HGpVtavBlwQ7rTT7-QpoeQ_Bt5U0mpIcmyO1RHVDA7A2Fyp1Mllu412DV9qLhtUVJRTYqxpmQn8zGPxERQ2Eq63tCeSXI2UVcEsFWiPQnxR8gOm84PjkI4ivsuflLp4G8sOomq4_F11oVjHSFj8kMpr0upBqbeVsOSA5GY_g7lLxPh_MFond45D4WxW5PLIMoOr2j2YeXjV5WJjwNyE_5_NMR6WKXEz-F4B9TFfL1kbhBgRm5LS9j7rsXlsCsieBFHlKJiReuAJ4vH0GIxeA84O2OY-L-jwWAYlxWfgQDrfccpi2zz_7HdiWBQm9mcmqQMcRRMhimzDtnZXQHSX9zEBkxIvcEDEsInDc8KrnG3digkxTIAuhuLlULkMzDSmeQBtgjdSrxhUVCjW7QBVH6VEse65oWqTHEHKfp8AGxXfSd-h-qbx_S9HkMZ3e3itNsq3MIs5dfqi7wV0O7pwcTS2MqWtisNY2ZnUo7bd2l_FOimK59q1rM6IFpTPYpiO5MGpIm6ZnnhK3F2T8tbQrTV-qHatfYYkaIFfwIpGgQs6LSdht3dIHfOMN3nSI9wLyKAwL1QwmZYtxJIGnqHqgH4k=w1200-h800-no)

CryoSat-2 clearly has Jan 2012 and 2013 thinner than Jan 2017. But PIOMAS has this:

(https://lh3.googleusercontent.com/vaCYDW_AYFn1nxuvWg4RD9Zuv9UrwCTQDupgM4qa9dfcS-3zRXB4SY2GOFxW6n93OUi1-A2Zl3L6OHqC6xT2V2pnaaTWBcfwYE6Mt5ciQTtvlsQEGn_SWi_wc1zix7Y86A6z-dPriht3nVV9tUnrVZBfbxShd2DX2tm13uDPfgoZk61GFpmeu3uXzqdJaEFDpsUmxChNsqHaXOnKvGSwkvBNvghrJ_SxXU7ZGxNloBbjBuvZbehIxgNcS5ftG9NFtLEE9E3m4u2EOh8BiV8TwLU8VbKNQFLTzqGj9PIMuzo4Yp9qjqzv6UpkzlOLZoAHhH-JM4gfOZo2GWdUjoxuj7NZ-bkInacBk38urbowQNQH6MYBJUCF73z_4DxfMIo8YxhKzb2MibOUxq7HInl4URQfYXKP9KI-UFmvOaBwVuB7q59a_EXc4yPl_fm0RuD4H3fe0AZEJS494QQ_T2bLK13bpk5_PPsHv8YkXrxLKBeBjqJOI0xV0His7kXec2qjfZg3n0v6EqBkFPvUG69YgPZLCgHBZ8uzCU_ddTS6z5MGVxlMG_vyeuV1yML5Yd_n3ARCnaeOsgQq9EXz84uGw1NhVSAeJMf60wUAvckRwfOFrfttAb8d=w241-h199-no)

Difference with 2012 and 2013 at the end of January is 2270 and 1571 km3 respectively. Okay, CryoSat is showing an average, so let's the take the average of the differences with 2017 at Jan 1st and 31st: 2118 and 1193 km3 respectively.
There is a problem with the palette used in these maps, in that it is easier to distinguish ice from 2 to 4 m than from 0 to 2 m. Very difficult to compare the main extensions of ice which are under 2m !

Regarding Michael's comparison, to me it looks that for whatever reason Cryosat and PIOMAS best agree in FYI zones with independence of snow.
Title: Re: Piomas vs. CryoSat
Post by: seaicesailor on February 11, 2017, 12:01:01 PM
Why does 2017 map say Cryosat "NRT"? Is it maybe an enhanced version? That might invalidate comparison (just saying)
Title: Re: Piomas vs. CryoSat
Post by: Neven on February 11, 2017, 12:11:55 PM
There is a problem with the palette used in these maps, in that it is easier to distinguish ice from 2 to 4 m than from 0 to 2 m. Very difficult to compare the main extensions of ice which are under 2m !

I agree. I wish I could do more than eyeball. I don't even know how to count pixels.

I'll just wait for someone to come up with a graph of CryoSat-2 data for January, or look for the data myself. But even my eyeball can see that CryoSat considers Jan 2012 and 2013 to have lower volume than Jan 2017.
Title: Re: Piomas vs. CryoSat
Post by: shendric on February 11, 2017, 04:25:49 PM
Why does 2017 map say Cryosat "NRT"? Is it maybe an enhanced version? That might invalidate comparison (just saying)

NRT refers to the near real time data stream from ESA. January thicknesses based on the regular data will only be available at the beginning of March. The difference in sea ice thickness between both Cryosat input products is marginal though (see: http://www.the-cryosphere.net/10/2003/2016/ (http://www.the-cryosphere.net/10/2003/2016/)).

Title: Re: Piomas vs. CryoSat
Post by: shendric on February 11, 2017, 04:52:23 PM
Weird indeed.

I know we have discussed about it before but Wlwhat is Cryosat's skill in distinguishing snow?

Ku-Band radar (CryoSat) is sensitive to snow grain size. A larger anomaly in the snow microstructure (depth hoar, ice lenses) may result in too high freeboard/thickness values.
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on February 11, 2017, 08:21:07 PM

There is a problem with the palette used in these maps, in that it is easier to distinguish ice from 2 to 4 m than from 0 to 2 m. Very difficult to compare the main extensions of ice which are under 2m !


 ;)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimages.meteociel.fr%2Fim%2F322%2Fjan16vs17_cryosat2_epa0.gif&hash=ec9530cc134834fb7bda0b1120d67533)

Title: Re: Piomas vs. CryoSat
Post by: CognitiveBias on February 11, 2017, 08:23:58 PM
Now, that's funny!
Title: Re: Piomas vs. CryoSat
Post by: Neven on February 13, 2017, 10:30:12 AM
In another thread crandles remarked the following:


However, I have what is a rather different quibble. We seem to be saying FDD is low this year which will result in thinner ice. However there is a serious problem of cause and effect. At the other extreme, we could say there is less volume ie thin ice so heat transfers from ocean to atmosphere faster and therefore the atmosphere is warmer. So the low FDD could be a consequence of low volume and as there is fast transfer of heat from ocean to atmosphere, the volume of ice could be catching up to where it normally is. It isn't going to be one extreme or the other but some combination. Is it possible that the low volume and increased storminess could this year have altered the balance between the two causes making it more a case of ocean warming atmosphere. Then would using low FDD as a reason for low volume be giving a false indication of particularly low volume? Perhaps Cryosat2 data shouldn't be dismissed in favour of PIOMAS quite so readily?

And maybe there is more heat going through the ice because waters are warmer, either caused by absorption and mixing (during the melting season and fall), like Hyperion proposes (https://forum.arctic-sea-ice.net/index.php/topic,933.msg103039.html#msg103039) in the other thread. Or by a heat pulse brought in by ocean currents.

What speaks against this (heat coming out of the Arctic Ocean through the ice), is that we have seen all those lows bringing in heat (and moisture) from the Atlantic. This would also imply that there has been more snowfall on the ice and maybe that's what causes the difference between PIOMAS and CryoSat.

Because after the 2012 melting season there also was a lot of thin ice, but the Arctic didn't heat up nearly as much as now during the 2012/2013 freezing season. Quite the contrary, if my memory doesn't fail me.

Snow might explain the difference between CryoSat and PIOMAS. I've asked one scientist about snow depth data around the North Pole, compared to previous years, but the sensors failed quite quickly this year.
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on February 13, 2017, 11:10:57 AM
I think that the difference could be due to ice dynamics (drift, compaction).

I believe that PIOMAS is good at modelling the thermodynamics that affect the ice thickness , but maybe it is not so good at modelling the changes in thickness caused by drift, compaction and ridging of the ice.

 

Title: Re: Piomas vs. CryoSat
Post by: crandles on February 13, 2017, 11:30:09 AM
I've been thinking about that too - but came to the conclusion that if the ocean is warming the atmosphere more than heretofore, it is symptomatic of something new - and none of the possibilities I can think of seem ultimately conducive to higher than expected volume. viz:

 - thinner ice causing more ocean heat to be lost to the atmosphere. No volume increase there.
 - less snow cover causing greater heat loss and more freezing? Yes, but it's been stormy, so why would there be less snow? Also, the storms would seem to imply greater mixing with the warmer southern latitudes.
 - halocline breakdown. Ouch.

>"- thinner ice causing more ocean heat to be lost to the atmosphere. No volume increase there."

My reaction is depends on circumstances: If it is thinner ice allowing more heat to be lost then rate of heat loss is a good indicator of ice mass being formed. However if it is stormy weather stirring up heat from below then it is much less of a good indicator of ice mass formed.

Cause and effect problems are complicated and I am not at all sure I am getting my head around it all correctly. I have no real reason to think PIOMAS is not doing it all correctly. Nevertheless with the FDD total being so weird, I think we should be cautious and not go jumping too far ahead to too many conclusions.
Title: Re: Piomas vs. CryoSat
Post by: epiphyte on February 15, 2017, 04:20:43 PM
I've been thinking about that too - but came to the conclusion that if the ocean is warming the atmosphere more than heretofore, it is symptomatic of something new - and none of the possibilities I can think of seem ultimately conducive to higher than expected volume. viz:

 - thinner ice causing more ocean heat to be lost to the atmosphere. No volume increase there.
 - less snow cover causing greater heat loss and more freezing? Yes, but it's been stormy, so why would there be less snow? Also, the storms would seem to imply greater mixing with the warmer southern latitudes.
 - halocline breakdown. Ouch.

>"- thinner ice causing more ocean heat to be lost to the atmosphere. No volume increase there."

My reaction is depends on circumstances: If it is thinner ice allowing more heat to be lost then rate of heat loss is a good indicator of ice mass being formed. However if it is stormy weather stirring up heat from below then it is much less of a good indicator of ice mass formed.

Cause and effect problems are complicated and I am not at all sure I am getting my head around it all correctly. I have no real reason to think PIOMAS is not doing it all correctly. Nevertheless with the FDD total being so weird, I think we should be cautious and not go jumping too far ahead to too many conclusions.

Concur on the first - even more so in the absence of snow cover - which is why I think beaufort might end up putting a fight this year by reaching near-normal volume. What I should have said to be clear was "no year-on-year volume increase there"

On the second , things in many areas are so different from normal that I see no reason to think that PIOMAS _is_ doing it correctly!
Title: Re: Piomas vs. CryoSat
Post by: seaicesailor on February 15, 2017, 09:08:54 PM

There is a problem with the palette used in these maps, in that it is easier to distinguish ice from 2 to 4 m than from 0 to 2 m. Very difficult to compare the main extensions of ice which are under 2m !


 ;)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimages.meteociel.fr%2Fim%2F322%2Fjan16vs17_cryosat2_epa0.gif&hash=ec9530cc134834fb7bda0b1120d67533)
Thank you Diablobanquisa. :)

Title: Re: Piomas vs. CryoSat
Post by: Neven on February 16, 2017, 10:25:18 PM
I've been able to look some more into this, with the help of Michael, who sent me the data that allowed me to create this graph:

(https://lh3.googleusercontent.com/6jRsgGfz3uf16mwg1UNPCC77bpKnyzZUExYRel7QovPU0xd3C22nDqipFHb-T87ALjHhbbgpMzkB7a-FskbjVEvjKF36LSxPdaPWJYNCNddQpGZ2_H5aWkSX4riiNGuejdtUqh0-hqZZiNMXCXx7zJiAbJtst7qlMmhtNenA5L3eAcnKXCcCy6Uv_T6tovRjfJAdoQilAiMvkDqYRQvOFwelZN5_24evZwyiASKosvJ8s0RbZY8lhdmvBLqUemu7Tt-dxI5XIeFSw3gbl_TFEcTAEwUnvtA-umDyIngnss4IMdkdDrJIvVFDun_h0a6fG895AXwmXNoPmMkJRKWdJunia45hSg8YRN0HIQCYL6NcVq-yRaaMZVmdxCoLWVjsPcDCYOuQZYKItfwKzGMnEg6NMOoGGN0MJg0YeDXzqqlVT9pKLCGmfNq_9_hwjCUbLmdhoqPjcWuOz4_JK0-0dw9DnEiNDgXAHYKcA9HZzkW6_azr1EncBVdFQSUIGCjBLEqSs2R6IWVfkON_6oxp6BETy1MDwm_8YSNQUnWIZhdd-_Pn0oGGV_mGV0VNyhXs3lEpXkWh2Q6rBcTgBJy97fMs4KkbXDLi5INFO-Hxuf6IKLI7zv3B=w799-h332-no)

Michael sent me the CryoSat-2 data from AWI (CryoSat-2 average volume on a combined PIOMAS-AWI grid), and I simply added the daily PIOMAS volume data for January and then divided by 31 to get an average as well.

As you can see the trend lines more or less move the same way, except for this year. According to CryoSat-2 there is slightly more volume now than last year and so the trend line goes up a bit. For PIOMAS the trend line crashes.

The same thing happens in December:

(https://lh3.googleusercontent.com/l0704PJVo0xXZyxZvyAN6WFZPfxbpM8ax89iq2H9xgutFScqsrRAwwuHsBKLUiVuq1vUFSTu8mLU2USRqSVxoOnYfy9w1RIjGI9jAMNYbWrMqWOVI33ej-0Ok8Kn5HMX_4Iylx3TDTujPvjAb7waiW12wJMam5TxSO69qnNysXwmiY3eul509n7SjQ0_D3GyOYMHnnkxq_5v8S7gIDuS5n1qtzTMAxcD3K_1bzuxoHcL7_v48Rr0J6z8OQPIDsuEij1FpoL7OQooCmsdeXqFZJG7t-pvPskMjYPnHmjwNqqdtW1fLLkjhEQ4AwaGxHECQjV1QBGZYevd-nQzkVGaYPeicNfDEKwm7_cUk9ItEBoPQLsI0TX2jgQFv9ogQwqVYj6msiRnFs5S1NBfBu_Ei4y2cB1lrD4TtR41AcVoSLV1ePM8jk33GGh-ICYMGVTVBm5Y9siXb2aNyAsGX8XaJ8w_W7kshIWoKuNuJcDq6EGmFZIkajM6NFvxX1mAM36jpMIswZ3r678YkEl_Be_k1HMLHotQtUANBC1Y3THorqAiaSbi6J1W65GqlHMIUc9-NnERa9eMazNLEuPjCLmkyog5MBQ6gxrmqQxucF7TT_a6-NhM_bnY=w799-h332-no)

As shendric said:

Ku-Band radar (CryoSat) is sensitive to snow grain size. A larger anomaly in the snow microstructure (depth hoar, ice lenses) may result in too high freeboard/thickness values.

This is most probably the reason for this enormous divergence, as there have been so many Atlantic storms hurled into the Arctic this winter.

Here are a couple of quotes from Robert Ricker's PhD thesis paper (https://epic.awi.de/37878/1/PhD_20150312_robertricker.pdf). Abstract:

Radar altimetry measurements of the current satellite mission CryoSat-2 show an increase of Arctic sea-ice thickness in autumn 2013, compared to previous years but also related to March 2013. Such an increase over the melting season seems unlikely and needs to be investigated. Recent studies show that the influence of the snow cover is not negligible and can highly affect the CryoSat-2 range measurements if it is assumed that the main scattering horizon is given by the snow-ice interface. Our analysis of Arctic ice mass-balance buoy records and coincident CryoSat-2 data between 2012 and 2014 adds observational evidence to these findings. Linear trends of snow and ice freeboard measurements from buoys and nearby CryoSat-2 freeboard retrievals are calculated during accumulation events. We find a positive correlation between buoy snow-freeboard and CryoSat-2 freeboard estimates, revealing that early snow accumulation might have caused a bias in CryoSat-2 sea-ice thickness in autumn 2013.

Look at the December graph where you can clearly see a similar jump (relative to PIOMAS) in 2013.

More quotes:

Moreover, backscatter from both interfaces superimpose each other and cause broadened radar returns, which is largest for snow depths >20 cm (Kwok, 2014). As a result, freeboard estimates can be biased high with the presence of thick snow layers.

(...)

For wet snow at the beginning and the end of the melting season, the dielectric properties of the snow layer might even limit the physical penetration of radar waves.

(...)

We hypothesize that the snow cover significantly affects the CS-2 freeboard retrieval by snow backscatter which would affect also sea-ice thickness and volume, independently of the range retrieval method.

(...)

We find high differences of up to 45 cm (30 cm) for the 40 % threshold retrieval and up to 30 cm (20 cm) for the 80 % threshold retrieval from the comparison between November 2013 and 2012 (November 2013 and March 2013) north of Canada.

(...)

It is still difficult to quantify the snow-scatter induced bias without knowledge of the regional distribution and temporal evolution of snow depth and snow stratigraphy. Snow, accumulated early, may undergo a partial melting and subsequent freezing as well as wind compaction. This leads to a very heterogeneous snow density distribution, while for the propagation of the Ku-band signal it is widely assumed that the snow density is homogeneous. In this way formed layers may affect the location of the main reflecting horizon.

(...)

 We conclude that snowfall can have a significant impact on CryoSat-2 range measurements and therefore on ice freeboard, thickness and volume. The assumption that the CryoSat-2 main scattering horizon is given by the snow-ice interface cannot be justified in regions with a thick snow layer.

My preliminary conclusions:

- PIOMAS has it more right than CryoSat-2, although probably underestimating thickness slightly.
- The discrepancy is caused by either a thick snow layer, or short melt events due to heat incursions changing the snow stratigraphy, or a combination of both.
- Bad news for the ice, as 1) snow insulates, causing the ice to thicken less, 2) snow melts more easily than ice, which can set off feedback processes earlier (melt ponding, etc), especially if it has already melted for short periods during the winter-spring transition (Stroeve published a paper about this last year).

Questions:

- Is there any observational data (buoys, atmospheric data) that enables us to quantify this, or...
- Give an idea of which areas are affected most? Unfortunately PIOMAS seems to be experiencing a problem (that bulge of thick ice hovering over Fram Strait), so I don't know how useful a regional breakdown would be.

Either way, this is pretty big, IMO, as it tells us something about snow depth on the sea ice which may have consequences for the state in which the ice pack enters the melting season.

I might write about it on the blog, or mention it in the next PIOMAS update, but I thought I'd share it here first. Maybe together we can squeeze more out of this.
Title: Re: Piomas vs. CryoSat
Post by: Jim Williams on February 17, 2017, 12:00:08 AM
I've been able to look some more into this, with the help of Michael, who sent me the data that allowed me to create this graph:

(https://lh3.googleusercontent.com/6jRsgGfz3uf16mwg1UNPCC77bpKnyzZUExYRel7QovPU0xd3C22nDqipFHb-T87ALjHhbbgpMzkB7a-FskbjVEvjKF36LSxPdaPWJYNCNddQpGZ2_H5aWkSX4riiNGuejdtUqh0-hqZZiNMXCXx7zJiAbJtst7qlMmhtNenA5L3eAcnKXCcCy6Uv_T6tovRjfJAdoQilAiMvkDqYRQvOFwelZN5_24evZwyiASKosvJ8s0RbZY8lhdmvBLqUemu7Tt-dxI5XIeFSw3gbl_TFEcTAEwUnvtA-umDyIngnss4IMdkdDrJIvVFDun_h0a6fG895AXwmXNoPmMkJRKWdJunia45hSg8YRN0HIQCYL6NcVq-yRaaMZVmdxCoLWVjsPcDCYOuQZYKItfwKzGMnEg6NMOoGGN0MJg0YeDXzqqlVT9pKLCGmfNq_9_hwjCUbLmdhoqPjcWuOz4_JK0-0dw9DnEiNDgXAHYKcA9HZzkW6_azr1EncBVdFQSUIGCjBLEqSs2R6IWVfkON_6oxp6BETy1MDwm_8YSNQUnWIZhdd-_Pn0oGGV_mGV0VNyhXs3lEpXkWh2Q6rBcTgBJy97fMs4KkbXDLi5INFO-Hxuf6IKLI7zv3B=w799-h332-no)

Michael sent me the CryoSat-2 data from AWI (CryoSat-2 average volume on a combined PIOMAS-AWI grid), and I simply added the daily PIOMAS volume data for January and then divided by 31 to get an average as well.

As you can see the trend lines more or less move the same way, except for this year. According to CryoSat-2 there is slightly more volume now than last year and so the trend line goes up a bit. For PIOMAS the trend line crashes.

The same thing happens in December:

(https://lh3.googleusercontent.com/l0704PJVo0xXZyxZvyAN6WFZPfxbpM8ax89iq2H9xgutFScqsrRAwwuHsBKLUiVuq1vUFSTu8mLU2USRqSVxoOnYfy9w1RIjGI9jAMNYbWrMqWOVI33ej-0Ok8Kn5HMX_4Iylx3TDTujPvjAb7waiW12wJMam5TxSO69qnNysXwmiY3eul509n7SjQ0_D3GyOYMHnnkxq_5v8S7gIDuS5n1qtzTMAxcD3K_1bzuxoHcL7_v48Rr0J6z8OQPIDsuEij1FpoL7OQooCmsdeXqFZJG7t-pvPskMjYPnHmjwNqqdtW1fLLkjhEQ4AwaGxHECQjV1QBGZYevd-nQzkVGaYPeicNfDEKwm7_cUk9ItEBoPQLsI0TX2jgQFv9ogQwqVYj6msiRnFs5S1NBfBu_Ei4y2cB1lrD4TtR41AcVoSLV1ePM8jk33GGh-ICYMGVTVBm5Y9siXb2aNyAsGX8XaJ8w_W7kshIWoKuNuJcDq6EGmFZIkajM6NFvxX1mAM36jpMIswZ3r678YkEl_Be_k1HMLHotQtUANBC1Y3THorqAiaSbi6J1W65GqlHMIUc9-NnERa9eMazNLEuPjCLmkyog5MBQ6gxrmqQxucF7TT_a6-NhM_bnY=w799-h332-no)

As shendric said:

Ku-Band radar (CryoSat) is sensitive to snow grain size. A larger anomaly in the snow microstructure (depth hoar, ice lenses) may result in too high freeboard/thickness values.

This is most probably the reason for this enormous divergence, as there have been so many Atlantic storms hurled into the Arctic this winter.

Here are a couple of quotes from Robert Ricker's PhD thesis paper (https://epic.awi.de/37878/1/PhD_20150312_robertricker.pdf). Abstract:

Radar altimetry measurements of the current satellite mission CryoSat-2 show an increase of Arctic sea-ice thickness in autumn 2013, compared to previous years but also related to March 2013. Such an increase over the melting season seems unlikely and needs to be investigated. Recent studies show that the influence of the snow cover is not negligible and can highly affect the CryoSat-2 range measurements if it is assumed that the main scattering horizon is given by the snow-ice interface. Our analysis of Arctic ice mass-balance buoy records and coincident CryoSat-2 data between 2012 and 2014 adds observational evidence to these findings. Linear trends of snow and ice freeboard measurements from buoys and nearby CryoSat-2 freeboard retrievals are calculated during accumulation events. We find a positive correlation between buoy snow-freeboard and CryoSat-2 freeboard estimates, revealing that early snow accumulation might have caused a bias in CryoSat-2 sea-ice thickness in autumn 2013.

Look at the December graph where you can clearly see a similar jump (relative to PIOMAS) in 2013.

More quotes:

Moreover, backscatter from both interfaces superimpose each other and cause broadened radar returns, which is largest for snow depths >20 cm (Kwok, 2014). As a result, freeboard estimates can be biased high with the presence of thick snow layers.

(...)

For wet snow at the beginning and the end of the melting season, the dielectric properties of the snow layer might even limit the physical penetration of radar waves.

(...)

We hypothesize that the snow cover significantly affects the CS-2 freeboard retrieval by snow backscatter which would affect also sea-ice thickness and volume, independently of the range retrieval method.

(...)

We find high differences of up to 45 cm (30 cm) for the 40 % threshold retrieval and up to 30 cm (20 cm) for the 80 % threshold retrieval from the comparison between November 2013 and 2012 (November 2013 and March 2013) north of Canada.

(...)

It is still difficult to quantify the snow-scatter induced bias without knowledge of the regional distribution and temporal evolution of snow depth and snow stratigraphy. Snow, accumulated early, may undergo a partial melting and subsequent freezing as well as wind compaction. This leads to a very heterogeneous snow density distribution, while for the propagation of the Ku-band signal it is widely assumed that the snow density is homogeneous. In this way formed layers may affect the location of the main reflecting horizon.

(...)

 We conclude that snowfall can have a significant impact on CryoSat-2 range measurements and therefore on ice freeboard, thickness and volume. The assumption that the CryoSat-2 main scattering horizon is given by the snow-ice interface cannot be justified in regions with a thick snow layer.

My preliminary conclusions:

- PIOMAS has it more right than CryoSat-2, although probably underestimating thickness slightly.
- The discrepancy is caused by either a thick snow layer, or short melt events due to heat incursions changing the snow stratigraphy, or a combination of both.
- Bad news for the ice, as 1) snow insulates, causing the ice to thicken less, 2) snow melts more easily than ice, which can set off feedback processes earlier (melt ponding, etc), especially if it has already melted for short periods during the winter-spring transition (Stoeve published a paper about this last year).

Questions:

- Is there any observational data (buoys, atmospheric data) that enables us to quantify this, or...
- Give an idea of which areas are affected most? Unfortunately PIOMAS seems to be experiencing a problem (that bulge of thick ice hovering over Fram Strait), so I don't know how useful a regional breakdown would be.

Either way, this is pretty big, IMO, as it tells us something about snow depth on the sea ice which may have consequences for the state in which the ice pack enters the melting season.
Neven, this is worthy of a blog post, if you wouldn't mind.
Title: Re: Piomas vs. CryoSat
Post by: crandles on February 17, 2017, 12:13:21 AM
Great post Neven.

Yes, thick snow and melt event causing various layers in the snow sounds much more likely than my don't get too carried away with FDD causing low volume because that might be cause and effect wrong way around.

Might layered snow be a more effective insulator as there is little scope for convection though snow layers?

Also snow layers could perhaps limit the scope for thick snow to remain dry on top by water trickling downwards so perhaps thick layered snow does loose its high albedo quickly?

That would be a bad combination but 2014 melt season was poor. However the Dec 2013 mismatch had corrected by Jan 2014 so perhaps we shouldn't expect a poor 2014 melt season.

2017 it hasn't corrected by Jan. Maybe it might correct itself by Feb or March?
Title: Re: Piomas vs. CryoSat
Post by: charles_oil on February 17, 2017, 08:38:21 PM
Is it possible that the snow is a significantly different grade / quality this year when the weather has been warmer than even last year ?   Thinking fine powder vs coarse "wetter" snow...
Title: Re: Piomas vs. CryoSat
Post by: Neven on February 17, 2017, 08:55:04 PM
I think there's simply more snow to start with. And then, on top of that, it may be that the snow's structure is such that it throws the CryoSat-2 radar waves off.

I want to look at SLP maps for all they months/years involved in the comparison to see if that can tell us something. Maybe some other maps as well.

Might layered snow be a more effective insulator as there is little scope for convection though snow layers?

Yes, perhaps. At the same time, it's the air bubbles in the snow that make it so insulative, I think. And I guess there's less air in layered snow.

That would be a bad combination but 2014 melt season was poor. However the Dec 2013 mismatch had corrected by Jan 2014 so perhaps we shouldn't expect a poor 2014 melt season.

I'm not seeing that. I see the PIOMAS trend line going in a straight line from 2013 to 2015, but CryoSat still has a spike (relatively speaking) in 2014. And it's still there in February, March and April.

It will be corrected once the snow melts and there is not as much snow during the next freeze-up.
Title: Re: Piomas vs. CryoSat
Post by: crandles on February 18, 2017, 01:32:57 PM
However the Dec 2013 mismatch had corrected by Jan 2014 so perhaps we shouldn't expect a poor 2014 melt season.

I'm not seeing that. I see the PIOMAS trend line going in a straight line from 2013 to 2015, but CryoSat still has a spike (relatively speaking) in 2014. And it's still there in February, March and April.

It will be corrected once the snow melts and there is not as much snow during the next freeze-up.

Perhaps yes. However, I don't think you should compare only with 2013 and 2015. The Jan 2014 gap of 2.5k is similar to 2011 and all the gaps are 2.5k to 3.5k with just one exception of 2017 gap of very weird 0.4k.

With Feb, yes 2014 is the smallest gap but this is no more unusual than 2013 being the largest gap.
Title: Re: Piomas vs. CryoSat
Post by: seaicesailor on February 18, 2017, 02:12:35 PM
I've been able to look some more into this, with the help of Michael, who sent me the data that allowed me to create this graph:
...
Of all this, what amazes most is your eyeballing capabilities. Man, that you were able to detect this from the Cryosat maps with the colors they have ...
Title: Re: Piomas vs. CryoSat
Post by: Neven on February 18, 2017, 08:11:04 PM
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.memorabletv.com%2Fwp-content%2Fuploads%2F2017%2F01%2Fmarty-feldman.jpg&hash=0322620fd4060d7cb5733ea0de517f47)

It was the difference with 2011 and 2012 that made me sure something was off (just by looking at the yellow colours).

Perhaps yes. However, I don't think you should compare only with 2013 and 2015. The Jan 2014 gap of 2.5k is similar to 2011 and all the gaps are 2.5k to 3.5k with just one exception of 2017 gap of very weird 0.4k.

With Feb, yes 2014 is the smallest gap but this is no more unusual than 2013 being the largest gap.

I was planning to look at the gaps today or tomorrow. Maybe I should divide one by the other, and thus create super data mutant CryoMAS! Just like CAPIE telling us about compactness, it will give us an idea of how much snow there is on the sea ice pack, compared to other years.

The problem is that it's difficult to align CryoSat-2 data with PIOMAS data, having to do with land masks and grid sizes, and what not. But Michael is looking into it. As soon as he has the time, he will send me data for both for the Central Arctic (or actually, the Arctic minus peripheral seas). That should be interesting.
Title: Re: Piomas vs. CryoSat
Post by: DrTskoul on February 18, 2017, 08:36:50 PM
That is why Neven's EyeCrometer is so powerful
..
Title: Re: Piomas vs. CryoSat
Post by: diablobanquisa on February 19, 2017, 06:41:11 PM
Hi Neven, have you considered whether the divergence between PIOMAS and CS2 could be due (at least partially) to ice dynamics, in addition to the 'snow-related' retrieval issue? (Kwok, R. 2015. Sea ice convergence along the Arctic coasts of Greenland and the Canadian Arctic Archipelago: Variability and extremes (1992–2014). Geophysical Research Letters, http://onlinelibrary.wiley.com/doi/10.1002/2015GL065462/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015GL065462/abstract))

I have noticed that the divergence was already there in November...

(https://diablobanquisa.files.wordpress.com/2017/02/november.png)


... but it had dramatically deepen by the end of December:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimages.meteociel.fr%2Fim%2F8170%2FDECEMBER_hnq1.PNG&hash=098b6d219e3bf08b808ced9b28649b86)


What happened in December? Many things, of course ;)  But, regarding sea ice drift, we had this:

(https://diablobanquisa.files.wordpress.com/2017/02/20161201_20170101_coz7.png)


I think that this pattern could have caused compaction and ridging from the Atlantic side towards the North Pole, CAA and North Greenland. The drift during December 2016 reminds me of the pattern that Kwok argued to be the cause of the increase in thickness in summer 2013:

(https://nsidc.org/arcticseaicenews/files/2015/09/Figure5-350x629.png)
https://nsidc.org/arcticseaicenews/2015/09/2015_arctic-minimum/ (https://nsidc.org/arcticseaicenews/2015/09/2015_arctic-minimum/)


I think that this feature could be due to compaction and ridging...

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimages.meteociel.fr%2Fim%2F4697%2F3_tkx4.png&hash=07f10fe60b38dc8ed30742544c15088b)

... and it is just where one of the most striking differences between PIOMAS and CS2 seems to be located:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimages.meteociel.fr%2Fim%2F7381%2FDiff_210701_uxj0_oux0.png&hash=b2d877c5e58a90fffca5c0dda228160b)


Just another theory.

Title: Re: Piomas vs. CryoSat
Post by: Neven on February 19, 2017, 10:07:23 PM
Thanks, Diablo, that could have something to do with it as well. Either way, both factors seem for a large part to be caused by the series of Atlantic storms. If ridging does play a large part in this, the tables would be turned and it might be an indication that there could be a rebound this year. But I'm jumping to conclusions here.

I've notified the PIOMAS folks and they might ask around as well. So, let's see what happens.
Title: Re: Piomas vs. CryoSat
Post by: jdallen on February 20, 2017, 08:15:34 AM
Thanks, Diablo, that could have something to do with it as well. Either way, both factors seem for a large part to be caused by the series of Atlantic storms. If ridging does play a large part in this, the tables would be turned and it might be an indication that there could be a rebound this year. But I'm jumping to conclusions here.

I've notified the PIOMAS folks and they might ask around as well. So, let's see what happens.
Considering the deficit of cold weather, I'm at a loss as how we could possibly have a volume rebound at this juncture.  The thermodynamics don't justify it.
Title: Re: Piomas vs. CryoSat
Post by: DrTskoul on February 20, 2017, 10:05:24 PM
Thanks, Diablo, that could have something to do with it as well. Either way, both factors seem for a large part to be caused by the series of Atlantic storms. If ridging does play a large part in this, the tables would be turned and it might be an indication that there could be a rebound this year. But I'm jumping to conclusions here.

I've notified the PIOMAS folks and they might ask around as well. So, let's see what happens.
Considering the deficit of cold weather, I'm at a loss as how we could possibly have a volume rebound at this juncture.  The thermodynamics don't justify it.

Only mechanics (ridging etc)
Title: Re: Piomas vs. CryoSat
Post by: Neven on February 20, 2017, 10:13:18 PM
And new ice growing where the winds have pushed the ice away.
Title: Re: Piomas vs. CryoSat
Post by: jdallen on February 21, 2017, 01:46:27 AM
And new ice growing where the winds have pushed the ice away.
I'd be more optimistic and more in agreement were it not for the continuous melting along the Atlantic and export to melt from Baffin bay and Bering Sea.

New ice is forming, but I'm not sure it is overcoming that Volume loss.
Title: Re: Piomas vs. CryoSat
Post by: Archimid on February 21, 2017, 02:04:01 AM
Considering the deficit of cold weather, I'm at a loss as how we could possibly have a volume rebound at this juncture.  The thermodynamics don't justify it.

I think it has a lot to do with the jump in extent. If I understand it correctly, once ice forms the first .5m grow really fast, explaining the rapid jump in volume.

And new ice growing where the winds have pushed the ice away.

I would expect to see a corresponding spike in temperatures. If it is cold enough the spike might be too small to even be measured, but there should be a spike.
Title: Re: Piomas vs. CryoSat
Post by: Michael on February 24, 2017, 11:55:44 AM
To complement my earlier post where I compared average daily PIOMAS data with averaged CPOM 2 day CryoSat-2 data, here I have compared PIOMAS monthly data with AWI CryoSat-2 monthly data.

Because of the problems of reconciling the PIOMAS curvilinear orthogonal grid with the AWI azimuthal equal-area grid, the PIOMAS data are sampled using the EASE-2 1 km grid as a 25 x 25 subgrid of the EASE-2 25 km grid used by AWI.

Because the coverage of the Arctic by the CryoSat-2 satellite is incomplete on a monthly time scale, only those grid cell for which AWI report sea ice are included in the comparison.

The difference is calculated by subtracting AWI CryoSat-2 Sea Ice Thickness from POIMAS Sea Ice Thickness.
Title: Re: Piomas vs. CryoSat
Post by: Michael on March 10, 2017, 10:55:07 AM
CryoSat-2 derived Sea Ice Thickness for February 2017 is now available so it is possible to compare them with the PIOMAS model output.

As before, PIOMAS daily gridded data compared to CPOM 2 day 1 km Sea ice Thickness.

Diference is calculated as PIOMAS minus CPOM.
Title: Re: Piomas vs. CryoSat
Post by: Michael on March 10, 2017, 10:58:47 AM
Also as before, PIOMAS monthly gridded data compared to AWI Cryosat-2 Sea Ice Thickness.

Difference is calculated as PIOMAS minus AWI.
Title: Re: Piomas vs. CryoSat
Post by: epiphyte on March 10, 2017, 04:24:18 PM
CryoSat-2 derived Sea Ice Thickness for February 2017 is now available so it is possible to compare them with the PIOMAS model output.

As before, PIOMAS daily gridded data compared to CPOM 2 day 1 km Sea ice Thickness.

Diference is calculated as PIOMAS minus CPOM.

There are radial striations visible in the plots which apparently line up with the orbital plane of the satellite (i.e. 92 degrees - tangential to edge of 'pole hole'). These just have to be artifacts, don't they? Assuming so, and given that the difference in measured freeboard between the peaks and troughs is as much as 2-3m, (most visible between 75-85N on the Russian side) what are we to make of it?

Title: Re: Piomas vs. CryoSat
Post by: crandles on March 10, 2017, 04:42:36 PM
See http://www.cpom.ucl.ac.uk/csopr/seaice.html (http://www.cpom.ucl.ac.uk/csopr/seaice.html)
 and click on 2 days, 14 days and 28 days.

It takes a month to cover all the area shown so it seem likely a result of comparing thickness at dates up to a month apart.
Title: Re: Piomas vs. CryoSat
Post by: oren on March 10, 2017, 06:01:07 PM
The main difference, and the outstanding feature in PIOMAS this year, is the thick blob above Greenland. It's missing in both Cryosat and Hycom, at least in the magnitude alluded to by PIOMAS. I keep wondering about it, especially as it seems to be headed eventually towards the Fram which might cause a sharp drop in PIOMAS volume (if and when that happens).
Title: Re: Piomas vs. CryoSat
Post by: Michael on March 11, 2017, 09:29:18 PM
There are radial striations visible in the plots which apparently line up with the orbital plane of the satellite (i.e. 92 degrees - tangential to edge of 'pole hole'). These just have to be artifacts, don't they?
The radial striations are due to the CryoSat-2 Satellite having limited coverage. Adjacent grid cells may contain data dated many days apart.

The CryoSat-2 satellite has a nominal orbital periodicity of 100 minutes, which means there are 14 to 15 orbits a day. Combine that with the fact that the SIRAL instrument uses “Synthetic aperture radar altimetry” to reduce the size of the instrument footprint to approximately 0.3 km by 1.5 km along track and across track, respectively (Laxon et al 2013), means that the area covered in one day is relatively small.

To help overcome this paucity of information, AWI use a 25 km grid. While CPOM utilise a gridding procedure that gives each data point a footprint roughly 10 km in diameter on the 1 km grid, and 50 km in diameter on the 5 km grid.

To illustrate this limited coverage I have done a comparison between the PIOMAS daily gridded data and CPOM 2 day 1 km data for 27_28 February 2017, on the EASE-2 12.5 km grid.Even this is potentialy misleading because the satellite track is much narrower than shown and there are two days worth of orbital tracks.

http://onlinelibrary.wiley.com/doi/10.1002/grl.50193/abstract (http://onlinelibrary.wiley.com/doi/10.1002/grl.50193/abstract)
Title: Re: Piomas vs. CryoSat
Post by: epiphyte on March 12, 2017, 04:20:46 PM
There are radial striations visible in the plots which apparently line up with the orbital plane of the satellite (i.e. 92 degrees - tangential to edge of 'pole hole'). These just have to be artifacts, don't they?
The radial striations are due to the CryoSat-2 Satellite having limited coverage. Adjacent grid cells may contain data dated many days apart.

The CryoSat-2 satellite has a nominal orbital periodicity of 100 minutes, which means there are 14 to 15 orbits a day. Combine that with the fact that the SIRAL instrument uses “Synthetic aperture radar altimetry” to reduce the size of the instrument footprint to approximately 0.3 km by 1.5 km along track and across track, respectively (Laxon et al 2013), means that the area covered in one day is relatively small.

To help overcome this paucity of information, AWI use a 25 km grid. While CPOM utilise a gridding procedure that gives each data point a footprint roughly 10 km in diameter on the 1 km grid, and 50 km in diameter on the 5 km grid.

To illustrate this limited coverage I have done a comparison between the PIOMAS daily gridded data and CPOM 2 day 1 km data for 27_28 February 2017, on the EASE-2 12.5 km grid.Even this is potentialy misleading because the satellite track is much narrower than shown and there are two days worth of orbital tracks.

http://onlinelibrary.wiley.com/doi/10.1002/grl.50193/abstract (http://onlinelibrary.wiley.com/doi/10.1002/grl.50193/abstract)
Title: Re: Piomas vs. CryoSat
Post by: Neven on March 27, 2017, 09:50:15 PM
Maybe they've been reading here, but it seems people at the NSIDC are aware (http://nsidc.org/arcticseaicenews/2017/03/arctic-sea-ice-maximum-at-record-low/) of the situation:

Data from the European Space Agency’s CryoSat-2 satellite indicate that this winter’s ice cover may be only slightly thinner than that observed at this time of year for the past four years. However, an ice-ocean model at the University of Washington (PIOMAS) that incorporates observed weather conditions suggests the volume of ice in the Arctic is unusually low.
Title: Re: Piomas vs. CryoSat
Post by: epiphyte on March 28, 2017, 07:52:57 AM
Maybe they've been reading here, but it seems people at the NSIDC are aware (http://nsidc.org/arcticseaicenews/2017/03/arctic-sea-ice-maximum-at-record-low/) of the situation:

Data from the European Space Agency’s CryoSat-2 satellite indicate that this winter’s ice cover may be only slightly thinner than that observed at this time of year for the past four years. However, an ice-ocean model at the University of Washington (PIOMAS) that incorporates observed weather conditions suggests the volume of ice in the Arctic is unusually low.

...and am I correct in saying that in Beaufort, at least, the (few) on-the-ground thickness measurements (from the new 2017 IMBs) indicate that PIOMAS may itself be somewhat on the high side?

Title: Re: Piomas vs. CryoSat
Post by: Peter Ellis on March 28, 2017, 11:03:19 AM
...and am I correct in saying that in Beaufort, at least, the (few) on-the-ground thickness measurements (from the new 2017 IMBs) indicate that PIOMAS may itself be somewhat on the high side?

"few" = one.  One is the number of active IMBs measuring thickness, and the number of the buoys shall be... one.

And no.  A point measurement cannot be easily compared to PIOMAS, which actually has an entire distribution baked into every pixel - X% at one thickness, Y% at a different thickness, etc.  The numbers reported and used for the graphs are the "grid box effective thickness" which is a sort of average over the whole pixel.

When a buoy is placed, it's likely to be in a thinner spot than average, because the average is pulled upwards by ridges and hummocks.  Nobody is going to drill down through the middle of an ice ridge to place a buoy.

Remember what arctic ice actually looks like - a rolling landscape with flat fields (floe ice), hummocks (deformed ice) and hedges (ridges between floes).  Over half of all the ice volume is in the ridges, and the buoys don't see those at all.
Title: Re: Piomas vs. CryoSat
Post by: Neven on March 28, 2017, 11:14:03 AM
All we can do is wait for the results of Operation IceBridge to come in, and hope that will give us some more clues.
Title: Re: Piomas vs. CryoSat
Post by: Jim Hunt on March 28, 2017, 03:32:29 PM
...and am I correct in saying that in Beaufort, at least, the (few) on-the-ground thickness measurements (from the new 2017 IMBs) indicate that PIOMAS may itself be somewhat on the high side?

No, as Peter pointed out. If the buoy doesn't get crushed in a ridge it should give a good idea how thermodynamic thickening (and eventually melting) goes from here. 2017A will certainly be on first year ice, but we can't say with any certainty when the floe started to freeze. < 1m seems on the low side to me for ice that's been increasing in thickness all winter long, and the Canadian Ice Service maps show thicker ice in that area. However I haven't checked location/motion/temperature yet to see if that helps explain matters.

I've been too busy winding up Anthony Watts (http://greatwhitecon.info/2017/03/alice-f-convicted-in-wuwt-show-trial/) amongst others!

 
Title: Re: Piomas vs. CryoSat
Post by: epiphyte on March 29, 2017, 07:24:33 PM
...and am I correct in saying that in Beaufort, at least, the (few) on-the-ground thickness measurements (from the new 2017 IMBs) indicate that PIOMAS may itself be somewhat on the high side?

No, as Peter pointed out. If the buoy doesn't get crushed in a ridge it should give a good idea how thermodynamic thickening (and eventually melting) goes from here. 2017A will certainly be on first year ice, but we can't say with any certainty when the floe started to freeze. < 1m seems on the low side to me for ice that's been increasing in thickness all winter long, and the Canadian Ice Service maps show thicker ice in that area. However I haven't checked location/motion/temperature yet to see if that helps explain matters.

I've been too busy winding up Anthony Watts (http://greatwhitecon.info/2017/03/alice-f-convicted-in-wuwt-show-trial/) amongst others!

I wanted to mention that there's a recent sentinel 1 image of the neighborhood which may inform this discussion. FYI I just posted on it in the "What the Buoys are Telling Us" thread.
Title: Re: Piomas vs. CryoSat
Post by: Steven on March 30, 2017, 08:52:11 PM
New paper by Ricker et al.:

Satellite-observed drop of Arctic sea-ice growth in winter 2015-2016 (http://onlinelibrary.wiley.com/doi/10.1002/2016GL072244/abstract)

Abstract:
An anomalous warm winter 2015-16 lead to the lowest winter ice-extent and highlights the sensitivity of the Arctic sea ice. Here, we use the 6-year record of an improved sea-ice thickness product retrieved from data fusion of CryoSat-2 radar altimetry and SMOS radiometry measurements to examine the impact of recent temperature trend on the Arctic ice-mass balance. Between November 2015 and March 2016, we find a consistent drop of cumulative freezing degree days across the Arctic, with a negative peak anomaly of about 1000 degree days in the Barents Sea, coinciding with an Arctic-wide average thinning of 10 cm in March with respect to the 6-year average. In particular, the loss of ice volume is associated with a significant decline of March first-year ice volume by 13%. This reveals that due to the loss of multiyear ice during previous years, the Arctic ice cover becomes more sensitive to climate anomalies.

(click to enlarge image:)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FRYwOZBG.png&hash=48b7f68095793b00efa45cf90496b032)
Title: Re: Piomas vs. CryoSat
Post by: Feeltheburn on March 31, 2017, 02:29:38 AM

...and am I correct in saying that in Beaufort, at least, the (few) on-the-ground thickness measurements (from the new 2017 IMBs) indicate that PIOMAS may itself be somewhat on the high side?

You could be on to something. According to DMI modeled ice thickness, the ice in Beaufort, especially near land, are thicker this year compared to last. If that is wrong, then DMI must be overestimating thickness overall. You can see this by clicking + and 1 365 days and comparing the two:

http://ocean.dmi.dk/arctic/icethickness/thk.uk.php (http://ocean.dmi.dk/arctic/icethickness/thk.uk.php)
Title: Re: Piomas vs. CryoSat
Post by: CognitiveBias on March 31, 2017, 04:41:30 PM
If you compare this year to last you see that the ice pulled off the Alaskan coast last year vs the Russian coast this year.  Overall the ice still looks worse this year.
Title: Re: PIOMAS vs CryoSat
Post by: Adam Ash on April 06, 2017, 01:27:06 AM
As soon as the CAA Garlic Press gets underway, all the remaining 'thick' ice will head south to oblivion.  Then all that will remain is a mush of barely-one-year-old ice filling the basin.  The risk of that melting out in anything like an above average melt season seems acute.

The atmospheric circulation arising from this year's melt season (ever more open water) re heat transport from equator to the Arctic will be very interesting to watch.  Are there any signs of the Ridiculously Resilient Ridge or its relations restoring itself?
Title: Re: PIOMAS vs CryoSat
Post by: DrTskoul on April 06, 2017, 01:39:39 AM
As soon as the CAA Garlic Press gets underway, all the remaining 'thick' ice will head south to oblivion.  Then all that will remain is a mush of barely-one-year-old ice filling the basin.  The risk of that melting out in anything like an above average melt season seems acute.

The atmospheric circulation arising from this year's melt season (ever more open water) re heat transport from equator to the Arctic will be very interesting to watch.  Are there any signs of the Ridiculously Resilient Ridge or its relations restoring itself?
+PDO has mixed things up in the Pacific. No news about RRR yet.
Title: Re: PIOMAS vs CryoSat
Post by: TerryM on April 06, 2017, 04:28:45 AM
FYI, with it's high salt content will melt at a lower temperatures than the much fresher MYI. Will a preponderance of FYI act to lower atmospheric temperatures, and if so could this be one of the  causes of the "rebound years" that seem so often to follow years with very little ice retention?


Terry
Title: Re: PIOMAS vs CryoSat
Post by: FishOutofWater on April 07, 2017, 04:06:55 AM
El Niño is brewing. With El Niño and the positive PDO the RRR is history. This winter, instead of the RRR we saw very strong blocking near the dateline. Blocking highs went up over Alaska and retrograded to Siberia over a week or two. The blocks in both the far north Atlantic and far north Pacific brought exceptional heat to the Arctic and heavy rains to California.

The positive phase of the PDO does not favor the strong ridge off of the Pacific northwest.
Title: Re: PIOMAS vs CryoSat
Post by: Okono on April 16, 2017, 03:58:36 AM
SST anomalies and wind vector anomalies continue to indicate the presence of the nega-blob, the inverse of the original blob.  The overlay with the classic blob is a little eerie in its symmetry.  I don't see the same obverse elsewhere, but I have no meteorological training, so I would rely on FishOutOfWater.

https://en.wikipedia.org/wiki/The_Blob_(Pacific_Ocean)

I have no idea whether the huge patch of cold water is cause or effect, but it's had plenty of effect here in California through the winter, dragging storms far enough south to give us some pretty good lashings.

Title: Re: PIOMAS vs CryoSat
Post by: epiphyte on April 16, 2017, 05:42:49 AM
SST anomalies and wind vector anomalies continue to indicate the presence of the nega-blob, the inverse of the original blob.  The overlay with the classic blob is a little eerie in its symmetry.  I don't see the same obverse elsewhere, but I have no meteorological training, so I would rely on FishOutOfWater.

https://en.wikipedia.org/wiki/The_Blob_(Pacific_Ocean)

I have no idea whether the huge patch of cold water is cause or effect, but it's had plenty of effect here in California through the winter, dragging storms far enough south to give us some pretty good lashings.

Hmmm. Well since the blob caused a blocking high, it doesn't seem unreasonable to surmise that the inverse blob might spawn all kinds of eastbound mayhem.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on April 25, 2017, 09:28:34 PM
CryoSat-2 derived Sea Ice Thickness for March 2017 is now available so it is possible to compare them with the PIOMAS model output.

As before, PIOMAS daily gridded data compared to CPOM 2 day 1 km Sea ice Thickness.

Difference is calculated as PIOMAS minus CPOM.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on April 25, 2017, 09:30:19 PM
Also as before, PIOMAS monthly gridded data compared to AWI Cryosat-2 Sea Ice Thickness.

Difference is calculated as PIOMAS minus AWI.
Title: Re: PIOMAS vs CryoSat
Post by: oren on April 25, 2017, 11:09:45 PM
Again, it seems PIOMAS places the thick blob away north of Greenland, while the actual very thick ice is not there but closer to the shore, as Hycom also shows.
What does that say about PIOMAS volume accuracy this year? I am quite concerned.
Title: Re: PIOMAS vs CryoSat
Post by: diablobanquisa on April 25, 2017, 11:44:08 PM
Sea ice thickness at the end of the freezing season according to CPOM Cryosat-2 data, 2016 vs. 2017:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimages.meteociel.fr%2Fim%2F9378%2F2016vs2017_wya9.png&hash=42576ed28a7eef269bc17d306d2a6287)


(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimages.meteociel.fr%2Fim%2F5765%2Foutput_Sf68DR_edu2.gif&hash=7c7490e01bb3095869072c225e990f63)



Title: Re: PIOMAS vs CryoSat
Post by: seaice.de on April 26, 2017, 12:06:48 AM
End of the season SMOS thickness / anomalies for comparison
Title: Re: PIOMAS vs CryoSat
Post by: Neven on April 26, 2017, 09:47:52 AM
Again, it seems PIOMAS places the thick blob away northbl of Greenland, while the actual very thick ice is not there but closer to the shore, as Hycom also shows.
What does that say about PIOMAS volume accuracy this year? I am quite concerned.

I've been told that they're looking into this.

End of the season SMOS thickness / anomalies for comparison

Is that compared to 2016?
Title: Re: PIOMAS vs CryoSat
Post by: seaice.de on April 26, 2017, 11:30:30 AM

End of the season SMOS thickness / anomalies for comparison

Is that compared to 2016?
Compared to the mean of all previous years since 2011. You have to click on the image to start the animation.

By the way, Spring means here 1st March to 15th April.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on May 04, 2017, 02:45:43 PM
CryoSat-2 derived Near Real Time Sea Ice Thickness for April is now available so it is possible to compare them with the PIOMAS model output.

As before, PIOMAS daily gridded data compared to CPOM 2 day 1 km Sea ice Thickness.

Difference is calculated as PIOMAS minus CPOM.

Things have changed fast in the last few days of April, see next post.

Do to a stupid error on my part the original images were inaccurate / misleading and have been replaced.
My apologises for the error.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on May 04, 2017, 02:50:51 PM
Also as before, PIOMAS monthly gridded data compared to AWI Cryosat-2 Near Real Time Sea Ice Thickness.

Difference is calculated as PIOMAS minus AWI.
Title: Re: PIOMAS vs CryoSat
Post by: Richard Rathbone on May 04, 2017, 05:53:35 PM
Is it just a color choice effect, or is there different data being used for the Cryosat plot and the Cryosat vs. PIOMAS plot? The satellite pass pattern is so much more obvious in the PIOMAS-Cryosat plot that it makes me wonder if there's some sort of smoothing step thats been omitted.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on May 04, 2017, 08:50:24 PM
Is it just a color choice effect, or is there different data being used for the Cryosat plot and the Cryosat vs. PIOMAS plot? The satellite pass pattern is so much more obvious in the PIOMAS-Cryosat plot that it makes me wonder if there's some sort of smoothing step thats been omitted.

No, do to a stupid error on my part there is an error in the calculation of the data for the PIOMAS plot which carries over to the CryoSat v PIOMAS plot, for which I apologise. The corrected plots will be posted as soon as they are finished.

The original graphics have been replaced.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on June 03, 2017, 10:43:01 AM
AWI only report their CryoSat-2 derived Sea Ice Thickness from October to April, but CPOM carried on reporting their data until 15 May 2017.

As there is no comparison with the AWI 25km data, I have used a 10km EASE-2 grid, as it better illustratres the sparceness of the CryoSat-2 data.

As before, PIOMAS daily gridded data compared to CPOM 2 day 1 km Sea ice Thickness.

Difference is calculated as PIOMAS minus CPOM.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on June 03, 2017, 10:46:42 AM
For those who like to make the comparison, here is PIOMAS for the end of May, using the DMI and HYCOM CICE palettes.
Title: Re: PIOMAS vs CryoSat
Post by: Neven on June 03, 2017, 01:36:03 PM
Thanks a lot for these images, Michael. And for sharing all that data and info.
Title: Re: PIOMAS vs CryoSat
Post by: seaicesailor on June 03, 2017, 01:42:04 PM
For those who like to make the comparison, here is PIOMAS for the end of May, using the DMI and HYCOM CICE palettes.
Finally the gif works
I made this comparison ACNFS vs PIOMAS.
Thanks a lot!
Title: Re: PIOMAS vs CryoSat
Post by: Michael on August 07, 2017, 06:45:10 PM
The nice people at the Alfred Wegener Institute (AWI) have released their "final" CryoSat-2 derived Sea Ice Thickness data for 2017. So for completeness here is a comparison with the PIOMAS monthly gridded thickness data.

The AWI CryoSat-2 data is provided on the EASE-2 25km grid, while the PIOMAS model uses an orthogonal curvilinear grid. Each 25km grid cell can contain elements of up to six PIOMAS grid cells, to overcome this the comparison is made on an EASE-2 0.5km grid, and the results are reported on an EASE-2 10km grid.

The PIOMAS grid is rendered on the 0.5km grid using polygons to approximate the curvilinear grid. This results in a maximum error of around 1km at the centre of the polygon faces. The result of this error is that each grid cell loses a small area to the grid cell in the row below and gains slightly less area from the grid cell in the row above. There is a similar error at the grid cell corners because the latitude & longitude co-ordinates for the PIOMAS grid are only provided to an accuracy of two decimal places. Close to the pole on the WGS84 spheroid this is only accurate to around 0.558km, and the error increases as you move south. The alternative is to use a nearest neighbour approach which is less accurate because it displaces the corners of the PIOMAS grid cells.

The CryoSat-2 satellite does not provide complete coverage of the whole Arctic in one calendar month. Also the CryoSat-2 Synthetic Aperture Radar has a narrow footprint and there is no guarantee that there will be 100% coverage within a 25km grid cell that reports Sea Ice Thickness in a particular calendar month.

To allow for this incomplete coverage, and because each 25km grid cell can contain elements of several PIOMAS grid cells, a Monthly Satellite Coverage Mask was used to ensure that a comparison was only made where CryoSat-2 measurements were actually available. The Monthly Satellite Coverage Masks were derived from the CPOM 2-day, 1km Sea Ice Thickness product.

The Difference is calculated by subtracting AWI from PIOMAS.

NOTE: In making this comparison I am not comparing like with like. The PIOMAS model reports Effective Sea Ice Thickness, while AWI report the weighted average of the CryoSat-2 data points in a 25km grid cell.
Title: Re: PIOMAS vs CryoSat
Post by: A-Team on August 07, 2017, 11:00:13 PM
Nice work, Michael!

Do you perchance have the maps colored in terms of percent differences, ie (piomas - awi)/piomas and (piomas - awi)/awi?

It seems to me (taking awi as experimentally observed) that piomas thickness errors can be colossal. For example, the artifactual blob near the pole that we've been discussing for months is off by over 2.5 m in January. If the ice were actually 1 m thick with piomas reporting 3.5, then (piomas - awi)/awi = 250%.

Overall, this would translate to a very substantial absolute uncertainty in volume (though not necessarily in piomas vs piomas month to month or even year to year change). The invidious comparison I have in mind is the volume of ice sitting over Greenland as measured by GRACE,  which is vastly more certain.

The visualization below rescales the four months to forum 700 pxl width in nsidc 'greenland down' orientation. It's noteworthy that the significant differences, both ±, remain fairly consistent in location (after adjusting for ice periphery) but moderate in degree as spring progresses. Since cryosat error does not have this locational bias, this consistency suggests that it is piomas that is off the mark.

Could you possibly elaborate on what 'effective ice thickness' for piomas means in terms of the model making experimentally testable predictions?

That is, suppose we had an unlimited budget for a daily helicopter-borne em induction + altimeter flying a dense grid over a particular piomas cell plus a ground-crew transect of ice cores (like we had this year north of Alert).

Those numbers are apples. But it's not clear what piomas is putting on the table: are 'effective ice thickness' numbers validatable or refutable by measurement or instead some sort of abstract (non-physical) construct?
Title: Re: PIOMAS vs CryoSat
Post by: greatdying2 on August 07, 2017, 11:44:49 PM
Terrific! Thank you Michael.

Did AWI (or anyone else) make maps yet of the original (as opposed to the difference with PIOMAS) thickness detected by Icesat?
Title: Re: PIOMAS vs CryoSat
Post by: greatdying2 on August 08, 2017, 12:46:58 AM
Here is an overlay of Michael's difference map with Wipneus' map of PIOMAS thickness, both from April.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on August 08, 2017, 08:44:27 AM

Do you perchance have the maps colored in terms of percent differences, ie (piomas - awi)/piomas and (piomas - awi)/awi?

Short answer, no. I would need to do rather a lot of work to come up with those numbers.

Could you possibly elaborate on what 'effective ice thickness' for piomas means in terms of the model making experimentally testable predictions?

The PIOMAS model outputs the distribution of sea ice in a grid cell in terms of the proportion of that ice in 12 thickenss bands. Effective ice thickness is simply the thickness that would result from spreading the ice evenly across the whole grid cell. So wherever you look within the grid cell the ice would be unbroken and of equal thickness. In terms of the thickness of the ice at a particular point in the grid cell, the thickness distribution can be read as a probablity distribution, which will give you the probability of the ice at that point in the grid cell lying in a particular thickness band.

It is worth remembering that CryoSat-2 derived sea ice thickness is still experimental, and that there are still uncertainties with regard to many aspects of the process. Also, CryoSat-2 provides a very sparse dataset, and that there is wide temporal spread within these AWI data.

It will be interesting to see how CryoSat-2 and PIOMAS compare with Icebridge when the QuickLook data is released.
Title: Re: PIOMAS vs CryoSat
Post by: Rob Dekker on August 08, 2017, 10:40:16 AM
Michael, A-Team and GreatDying2 :
Is it fair to say that from this animation of PIOMAS-AWI :

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fforum.arctic-sea-ice.net%2Findex.php%3Faction%3Ddlattach%3Btopic%3D8.0%3Battach%3D49877%3Bimage&hash=4a1f60c264de7955ea251bf1260fa35d)

that at least w.r.t. Cryosat2 that PIOMAS overestimates thickness of the thinner ice on the boundaries of the Arctic basin, and possibly underestimates ice in the CAB ?

If so, it would explain some of the features in Wipneus' PIOMAS volume anomaly graph :
https://sites.google.com/site/arctischepinguin/home/piomas (https://sites.google.com/site/arctischepinguin/home/piomas)
and specifically the fast drop in June and the re-bound in July of the years that go low...
Title: Re: PIOMAS vs CryoSat
Post by: Michael on August 08, 2017, 08:45:47 PM
There are two sources for CryoSat-2 derived Sea Ice Thickness. The Alfred Wegener Institute (AWI), and the Centre for Polar Observation and Modelling (CPOM). I have not seen any comparison between these two products, so here is a comparison of the AWI final product and the CPOM 2 day, 1km NRT product for January to April 2017. There is no great difference between the NRT and final AWI products, so this seems a reasonable comparison.

For purposes of comparison, CPOM 2 day data was regridded onto the 25km EASE-2 grid used by AWI to create a monthly plot, and then a  simple comparison of the two monthly plots was made.

The difference is calculated by subtracting the AWI value from the CPOM value.

Did AWI (or anyone else) make maps yet of the original (as opposed to the difference with PIOMAS) thickness detected by Icesat?

See below.

Continued ...
Title: Re: PIOMAS vs CryoSat
Post by: Michael on August 08, 2017, 08:46:56 PM
... Continued
Title: Re: PIOMAS vs CryoSat
Post by: Michael on August 08, 2017, 08:48:21 PM
... Continued
Title: Re: PIOMAS vs CryoSat
Post by: Michael on August 08, 2017, 08:49:45 PM
... Continued
Title: Re: PIOMAS vs CryoSat
Post by: greatdying2 on August 08, 2017, 08:52:10 PM
Is it fair to say that from this animation of PIOMAS-AWI :

that at least w.r.t. Cryosat2 that PIOMAS overestimates thickness of the thinner ice on the boundaries of the Arctic basin, and possibly underestimates ice in the CAB ?

If so, it would explain some of the features in Wipneus' PIOMAS volume anomaly graph :
https://sites.google.com/site/arctischepinguin/home/piomas (https://sites.google.com/site/arctischepinguin/home/piomas)
and specifically the fast drop in June and the re-bound in July of the years that go low...

Yes, I completely agree.
Title: Re: PIOMAS vs CryoSat
Post by: greatdying2 on August 08, 2017, 08:54:46 PM
There are two sources for CryoSat-2 derived Sea Ice Thickness. The Alfred Wegener Institute (AWI), and the Centre for Polar Observation and Modelling (CPOM). I have not seen any comparison between these two products, so here is a comparison of the AWI final product and the CPOM 2 day, 1km NRT product for January to April 2017. There is no great difference between the NRT and final AWI products, so this seems a reasonable comparison.

Thank you again Michael. These are a great help.

So there do seem to be some systematic differences between AWI and CPOM; however, they are relatively low in magnitude, less than half a metre one way or the other except in certain small regions (immediately adjacent to Greenland and the CAA).

Nevertheless, if I am reading these correctly, CPOM agrees with PIOMAS (a bit) more closely than AWI does?
Title: Re: PIOMAS vs CryoSat
Post by: Michael on August 09, 2017, 02:04:15 PM
Nevertheless, if I am reading these correctly, CPOM agrees with PIOMAS (a bit) more closely than AWI does?
I have previously posted monthly comparisons of PIOMAS Sea Ice Thickness and CPOM CryoSat-2 derived Sea Ice Thickness. For convenience I am reposting them here reworked with the new colour bar.

The comparison is between PIOMAS hiday daily gridded Effective Sea Ice Thickness and the CPOM 2 day, 1 km NRT product.

The difference is calculated by subtracting the AWI value from the PIOMAS value.
Title: Re: PIOMAS vs CryoSat
Post by: Rob Dekker on August 10, 2017, 09:34:50 AM
The comparison is between PIOMAS hiday daily gridded Effective Sea Ice Thickness and the CPOM 2 day, 1 km NRT product.

The difference is calculated by subtracting the AWI value from the PIOMAS value.

Thanks Michael !
This still suggests that PIOMAS overestimates ice in the outer areas of the Basin w.r.t. Cryosat2.
This when that ice melts, PIOMAS records a large volume loss, explaining the fast drop in June in volume. Then once melting goes a bit deeper into the CAB, PIOMAS underestimate ice thickness there, which explains the 'rebound' we see in Wipneus' volume anomaly graph for the years that extent goes low :
https://sites.google.com/site/arctischepinguin/home/piomas

Result : Observations suggest that PIOMAS underestimates thickness of ice in the boundary of the Arctic Basin, and possibly overestimates ice thickness in the CAB.
Title: Re: PIOMAS vs CryoSat
Post by: Michael on August 10, 2017, 06:39:10 PM
Before making any firm judgements it is perhaps worth considering how reliable the CryoSat-2 derived Sea Ice Thickness is likely to be.

The SIRAL (Synthetic Aperture Interferometric Radar Altimeter) instrument on CryoSat-2 has a footprint of approximately 0.3 km along track by 1.5 km across track and requires 369 days to provide global coverage. So it would require well over 1000 "footprints" to cover a 25km grid cell.

In his original study, Laxon used a 0.4 degree latitude by 4 degree longitude grid, and required a minimum of 100 measurements in each cell. The 25km EASE-2 grid used by AWI is somewhat smaller than the grid used by Laxon, but the 100 measurement threshold would seem to be reasonable.

AWI provide data for the total number of valid sea-ice thickness data points inside each 25km grid cell, which indicate that around 49% of grid cells reporting sea ice fall below this threshold. This in itself does not invalidate those data, but as the random uncertainties of the individual measurements decreases with the square root of the data points inside each grid cell, it is worth considering.

Ricker, R., Hendricks, S., Helm, V., Skourup, H., and Davidson, M.: Sensitivity of CryoSat-2 Arctic sea-ice freeboard and thickness on radar-waveform interpretation, The Cryosphere, 8, 1607-1622, https://doi.org/10.5194/tc-8-1607-2014, (https://doi.org/10.5194/tc-8-1607-2014,) 2014.
https://www.the-cryosphere.net/8/1607/2014/ (https://www.the-cryosphere.net/8/1607/2014/)

Laxon S. W., K. A. Giles, A. L. Ridout, D. J. Wingham, R. Willatt, R. Cullen, R. Kwok, A. Schweiger, J. Zhang, C. Haas, S. Hendricks, R. Krishfield, N. Kurtz, S. Farrell and M. Davidson (2013), CryoSat-2 estimates of Arctic sea ice thickness and volume, Geophysical Research Letters, 40, doi:10.1002/grl.50193.
http://onlinelibrary.wiley.com/wol1/doi/10.1002/grl.50193/abstract (http://onlinelibrary.wiley.com/wol1/doi/10.1002/grl.50193/abstract)
Title: Re: PIOMAS vs CryoSat
Post by: Rob Dekker on August 11, 2017, 07:02:35 AM
A sample of 40-60 measurements per pixel indeed would imply a large uncertainty (SQRT(1/N)=2.5%).
However, spread out over the hundreds or thousand pixels in the outer Arctic Basin, the confidence interval of the determination of ice thickness should be pretty tight (much less than 0.25%).
Title: Re: PIOMAS vs CryoSat
Post by: Neven on September 04, 2017, 06:43:14 PM
I didn't know whcch thread would be best to post this, but here is probably okay:

Comparison of CryoSat-2 and ENVISAT radar freeboard over Arctic sea ice: toward an improved Envisat freeboard retrieval

Kevin Guerreiro1, Sara Fleury1, Elena Zakharova1,2, Alexei Kouraev1,2,3, Frédérique Rémy1, and Philippe Maisongrande1

Abstract. Over the past decade, sea-ice freeboard has been monitored with various satellite altimetric missions with the aim of producing long-term time series of ice thickness. While recent studies have demonstrated the capacity of the CryoSat-2 mission (2010–present) to provide accurate freeboard measurements, the current estimates obtained with the Envisat mission (2002–2012) still require some large improvements.

In this study, we first estimate Envisat and CryoSat-2 radar freeboard by using the exact same processing algorithms. We then analyse the freeboard difference between the two estimates over the common winter periods (November 2010–April 2011 and November 2011–March 2012). The analysis of along-track data and gridded radar freeboard in conjunction with Envisat pulse-peakiness (PP) maps suggests that the discrepancy between the two sensors is related to the surface properties of sea-ice floes and to the use of a threshold retracker.

Based on the relation between the Envisat pulse peakiness and the radar freeboard difference between Envisat and CryoSat-2, we produce a monthly CryoSat-2-like version of Envisat freeboard. The improved Envisat data set freeboard displays a similar spatial distribution to CryoSat-2 (RMSD  =  1.5 cm) during the two ice growth seasons and for all months of the period of study.

The comparison of the altimetric data sets with in situ ice draught measurements during the common flight period shows that the improved Envisat data set (RMSE  =  12–28 cm) is as accurate as CryoSat-2 (RMSE  =  15–21 cm) and much more accurate than the uncorrected Envisat data set (RMSE  =  178–179 cm).

The comparison of the improved Envisat radar freeboard data set is then extended to the rest of the Envisat mission to demonstrate the validity of PP correction from the calibration period. The good agreement between the improved Envisat data set and the in situ ice draught data set (RMSE  =  13–32 cm) demonstrates the potential of the PP correction to produce accurate freeboard estimates over the entire Envisat mission lifetime.

link (https://www.the-cryosphere.net/11/2059/2017/)