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A-Team

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Re: PIOMAS vs CryoSat
« Reply #300 on: March 08, 2018, 04:01:38 PM »
Quote
CyroSat-2 does not measure snow depth
CryoSat-2 seeks to determine the freeboard of floating ice. The primary instrument is a synthetic aperture interferometric X-band radar altimeter. Precise altimetry alone has been found not to give accurate ice thickness -- hence the other 31 companion files (such as ice density) in the netCDF under discussion.

These are not taken from generic FYI/MYI climatology, as follows already from the map mismatch with snow depth and density (and good agreement with precip-modeled RASM-ESRL). Here we can benefit from recent papers such as:

Effect of Snow Salinity on CryoSat-2 Arctic First-Year Sea Ice Freeboard Measurements
V Nandan et al
http://onlinelibrary.wiley.com/doi/10.1002/2017GL074506/full

A weekly Arctic sea-ice thickness data record from merged CryoSat-2 and SMOS satellite data
R Ricker et al
https://www.the-cryosphere.net/11/1607/2017/
https://www.ifm.uni-hamburg.de/en/institute/staff/kaleschke/publicationskaleschke.html

Thin Sea Ice, Thick Snow, and Widespread Negative Freeboard Observed During N-ICE2015
A Rösel et al
http://onlinelibrary.wiley.com/doi/10.1002/2017JC012865/full

Note the radar reflection horizon is not necessarily the top surface of the ice nor the top surface of the snow. Locally, there may have been extruded or deposited brine salinity, snow on refrozen rain on snow, or snow melt in the dead of winter from advected semi-tropical moisture and abnormal temperatures.

Whatever, it adds to the mass afloat, though snow (granulated ice) lacks other mechanical, thermal, dynamical and volumetric properties of ice. We are not after freeboard per se but a more nuanced understanding of the heterogeneously distributed composite out there.

The question here is where does this netCDF file get its snow depth, snow depth uncertainty, snow density, snow density uncertainty from and how good are they. It is a near-real time winter product under active development, not a static journal article.

In the meantime, the companion files themselves are instructive even though we don't have a lot of people here who will click on them. The two uncertainty maps are shown below:
« Last Edit: March 08, 2018, 04:19:18 PM by A-Team »

Michael

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Re: PIOMAS vs CryoSat
« Reply #301 on: March 08, 2018, 04:29:27 PM »
Quote
CyroSat-2 does not measure snow depth
The question here is where does this netCDF file get its snow depth, snow depth uncertainty, snow density, snow density uncertainty from and how good are they. It is a near-real time winter product under active development, not a static journal article.
From the netCDF file data header:
source_auxdata_snow = "Warren, S.G., Rigor, I.G., Untersteiner, N., Radionov, V.F., Bryazgin, N.N., Aleksandrov, Y.I., and Colony, R.. Snow depth on Arctic sea ice. Journal of Climate, 12, 1814-1829, 1999"

Wipneus

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Re: PIOMAS vs CryoSat
« Reply #302 on: May 26, 2018, 03:31:32 PM »
In case you wondered like me why Cryosat-2 does not seem to be used to estimate Antarctic Sea Ice thickness, the following new (discussion) paper is of interest.

Kwok, R. and Kacimi, S.: Three years of sea ice freeboard, snow depth, and ice thickness of the Weddell Sea from Operation IceBridge and CryoSat-2, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-98, in review, 2018.

The abstract:
Quote
We examine the variability of sea ice freeboard, snow depth, and ice thickness in three years (2011, 2014, and 2016) of repeat surveys of an IceBridge (OIB) transect across the Weddell Sea. Averaged over this transect, ice thickness ranges from 2.4 ± 1.07 (2011) to 2.60 ± 1.15 m (2014), and snow depth from 30.0 ± 8.51 (2016) to 43.6 ± 10.2 cm (2014); suggesting a highly variable but broadly thicker ice cover compared to that inferred from drilling and ship-based measurements. Spatially, snow depth and ice thickness are higher in the more deformed ice of the western Weddell. Radar freeboards (uncompensated for snow thickness) from CryoSat-2 (CS-2), sampled along the same transect, are consistently higher (by up to 8 cm) than those computed using OIB data. This suggests radar scattering that originates above the snow-ice interface, possibly due to salinity in the basal layer of the snow column. Consequently, sea ice thickness computed using snow depth estimates solely from differencing OIB and CS-2 freeboards (without snow radar) are therefore general higher; mean differences in sea ice thickness along a transect are up to ~ 0.6 m higher (in 2014). This analysis is relevant to the use of differences between ICESat-2 and CS-2 freeboards to estimate snow depth for ice sea thickness calculations. Our analysis also suggests that, even with these expected biases, this is an improvement over the assumption that snow depth is equal to the total freeboard, where the underestimation of thickness could be up to a meter. Importantly, better characterization of the source of these biases is critical for obtaining improved estimates and understanding limits of retrievals of Weddell Sea ice thickness from satellite altimeters.

Reducing a bias from 1m to 60cm might have something to do with it.

The paper is in discussion until 20th July. The discussion can be followed on the link above, so far no comments have appeared.

Wipneus

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Re: PIOMAS vs CryoSat
« Reply #303 on: May 28, 2018, 04:32:59 PM »
In the same magazine another discussion paper focusing uncertainty in deriving thickness from Cryosat-2 measured free-board.

Price, D., Soltanzadeh, I., and Rack, W.: Snow depth uncertainty and its implications on satellite derived Antarctic sea ice thickness, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-92, in review, 2018.


The abstract:
Quote
Knowledge of the snow depth distribution on Antarctic sea ice is poor but is critical to obtaining sea ice thickness from satellite altimetry measurements of freeboard. We examine the usefulness of various snow products to provide snow depth information over Antarctic fast ice with a focus on a novel approach using a high-resolution numerical snow accumulation model (SnowModel). We compare this model to results from ECMWF ERA-Interim precipitation, EOS Aqua AMSR-E passive microwave snow depths and in situ measurements at the end of the sea ice growth season. The fast ice was segmented into three areas by fastening date and the onset of snow accumulation was calibrated to these dates. SnowModel falls within 0.02 m snow water equivalent (swe) of in situ measurements across the entire study area, but exhibits deviations of 0.05 m swe from these measurements in the east where large topographic features appear to have caused a positive bias in snow depth. AMSR-E provides swe values half that of SnowModel for the majority of the sea ice growth season. The coarser resolution ERA-Interim, not segmented for sea ice freeze up area reveals a mean swe value 0.01 m higher than in situ measurements. These various snow datasets and in situ information are used to infer sea ice thickness in combination with CryoSat-2 (CS-2) freeboard data. CS-2 is capable of capturing the seasonal trend of sea ice freeboard growth but thickness results are highly dependent on the assumptions involved in separating snow and ice freeboard. With various assumptions about the radar penetration into the snow cover, the sea ice thickness estimates vary by up to 2 m. However, we find the best agreement between CS-2 derived and in situ thickness when a radar penetration of 0.05-0.10 m into the snow cover is assumed.

"thickness estimates vary by up to 2 m.", that is hardly trivial.

The paper is in discussion until 23th July. The discussion can be followed on the link above, so far no comments have appeared.

Steven

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Re: PIOMAS vs CryoSat
« Reply #304 on: November 07, 2018, 06:46:39 PM »
There's a comparison of PIOMAS and CryoSat data for October 2018 at the PIOMAS website:

http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/

Quote
Ice thickness anomalies anomalies 2018 relative to 2011-2017 (Fig 6)  show widespread negative anomalies and with thicker than normal ice only in the eastern Beaufort Sea.  Thick ice in this area is to anomalous ice motion over the last 4 month that pushed sea ice against Banks Island and the western part of the Canadian Archipelago (Fig 7). This thickness anomaly pattern is supported by CryoSat thickness anomalies using the new version 2.1 from AWI. CryoSat thickness anomalies (Fig 9) are similar to PIOMAS but there are substantial differences in the Lincoln Sea and North of Fram Strait where CryoSat has positive anomalies.  PIOMAS and CryoSat time series for October times series show little further decline in October sea ice volume since the exceptionally low values first seen in  2011 and 2012 (Figure 10).

PIOMAS:

CryoSat:


oren

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Re: PIOMAS vs CryoSat
« Reply #305 on: November 07, 2018, 09:48:41 PM »
I must say the agreement is rather good in terms of the location of high and low volume anomaly areas, except in the (important) region between the pole and Greenland/CAA.

shendric

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Re: PIOMAS vs CryoSat
« Reply #306 on: November 08, 2018, 10:19:41 AM »
Just to let you know that the AWI CryoSat-2 data service has been resumed in the past days as can be seen by the PIOMAS - CryoSat-2 figures above. The CryoSat-2 sea ice thickness algorithm has been updated to version 2.1 with a number of changes:

  • Improved snow information for regions outside the central Arctic Ocean
  • new options for automated analysis (NSIDC region codes in gridded and orbit data
  • improved uncertainty for gridded sea ice thickness

We have also added online documentation and anonymous ftp access, you can find the necessary information here:

AWI CryoSat-2 wiki

Whats new in version 2.1


ftp://ftp.awi.de/sea_ice/product/cryosat2/v2p1/nh/

Cheers, Stefan

Neven

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Re: PIOMAS vs CryoSat
« Reply #307 on: November 08, 2018, 10:24:33 AM »
Thanks, Stefan!
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Neven

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Re: PIOMAS vs CryoSat
« Reply #308 on: February 10, 2019, 07:17:02 PM »
Maybe something interesting is going on again on this front. CryoSat-2 has ice thicker than 2011-2018 baseline north of Greenland and CAA, PIOMAS has it thinner.

I'll write about this in the next ASIB PIOMAS update. Anyone have any ideas what could be causing this? Another snow issue?
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epiphyte

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Re: PIOMAS vs CryoSat
« Reply #309 on: February 12, 2019, 03:31:17 AM »
Wildly uninformed speculation - but there has on and off been a large amount of open water in that area this winter. I've always wondered whether Cryosat might be prone to overestimate the average thickness of ice in fluid areas which have been subject to upheaval / repeated opening of wide polynyas followed by re-compaction of the thin ice formed on top of them during the hard winter. This might lead to a very non-uniform surface with sharp, high peaks and deep, snow-filled troughs.

Conversely, PIOMAS might underestimate the volume under such circumstances if it underestimates the area of open water and the faster rate at which it freezes vs. a uniform-thickness ice sheet.

Don't know if that's even $0.02 worth, of course :)


Tealight

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Re: PIOMAS vs CryoSat
« Reply #310 on: February 12, 2019, 10:58:59 AM »
Well this region has been very cold this winter, but we can only guess if this has translated into extra thickness. From Lebedev ice growth formula we know that sea ice over 2m grows very slowly no matter how cold the air is.

All I know for sure is that my AMSR2 thickness is high as well, but it is definitely affected by snow.

jdallen

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Re: PIOMAS vs CryoSat
« Reply #311 on: February 13, 2019, 04:15:21 AM »
Well this region has been very cold this winter, but we can only guess if this has translated into extra thickness. From Lebedev ice growth formula we know that sea ice over 2m grows very slowly no matter how cold the air is.

All I know for sure is that my AMSR2 thickness is high as well, but it is definitely affected by snow.
I'm HIGHLY suspicious of any model that shows large contiguous areas of ice with a thickness in excess of 3M, for exactly the reason you suggest.
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seaice.de

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Re: PIOMAS vs CryoSat
« Reply #312 on: February 13, 2019, 10:46:05 AM »
Well this region has been very cold this winter, but we can only guess if this has translated into extra thickness. From Lebedev ice growth formula we know that sea ice over 2m grows very slowly no matter how cold the air is.

All I know for sure is that my AMSR2 thickness is high as well, but it is definitely affected by snow.
I'm HIGHLY suspicious of any model that shows large contiguous areas of ice with a thickness in excess of 3M, for exactly the reason you suggest.
You can not trust these AMSR2 thickness maps. From these kind of microwave radiometer you can just derive a very uncertain proxy. For AMSR2 frequencies the penetration depth is not more than a few centimeters, therefore the signal comes just from the sea ice surface. It is rather related to snow grain sizes, layering and sea ice surface salinity.

Juan C. García

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Re: PIOMAS vs CryoSat
« Reply #313 on: October 16, 2019, 01:21:55 PM »
It is good to have it on this topic:
The Centre for Polar Observation and Monitoring have just published the first CryoSat-2 Arctic sea ice thickness map of the 2019/20 freezing season:

http://GreatWhiteCon.info/2019/10/facts-about-the-arctic-in-october-2019/#Oct-16

Quote
Note in particular the dark blue area north of the Canadian Arctic Archipelago.
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

gerontocrat

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Re: PIOMAS vs CryoSat
« Reply #314 on: October 16, 2019, 02:43:04 PM »
It is good to have it on this topic:
The Centre for Polar Observation and Monitoring have just published the first CryoSat-2 Arctic sea ice thickness map of the 2019/20 freezing season:

http://GreatWhiteCon.info/2019/10/facts-about-the-arctic-in-october-2019/#Oct-16

Quote
Note in particular the dark blue area north of the Canadian Arctic Archipelago.
The CryoSat-2 image is from the laser thingy, from which estimates of freeboard are generated from which estimates of thickness are made, i.e. starting with a physical measure of the ice, not from a model ?

If so, do we have any info if the Polar Science Center are doing comparisons of their model data with CyoSat-2 data? After all, they can find day, time of day and physical location from both datasets to look for close matches ?
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Jim Hunt

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Re: PIOMAS vs CryoSat
« Reply #315 on: October 16, 2019, 02:54:58 PM »
The CryoSat-2 image is from the laser thingy?

IceSat-2 is "the laser thingy". CryoSat-2 is the "interferometric radar range-finder thingy":

https://en.wikipedia.org/wiki/CryoSat-2

It's a "measurement" of sorts, but still has to make assumptions about snow thickness to turn freeboard measurements into sea ice thickness numbers.
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gerontocrat

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Re: PIOMAS vs CryoSat
« Reply #316 on: October 16, 2019, 07:35:56 PM »
The CryoSat-2 image is from the laser thingy?

IceSat-2 is "the laser thingy". CryoSat-2 is the "interferometric radar range-finder thingy":

https://en.wikipedia.org/wiki/CryoSat-2

It's a "measurement" of sorts, but still has to make assumptions about snow thickness to turn freeboard measurements into sea ice thickness numbers.
And do we have any idea on the reliability of the assumptions of snow thickness ?

ps: Thingys
I was thinking about how the German Institute in Potsdam recently used IceSat-2 (or was it CryoSat-2) in conjunction with GRACE-FO to improve the quality of ice-mass loss measurement of the AIS and GIS and now have got the Sat-2's totally mixed up.

The technology moves on too fast for my fevered brain to keep up.
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Re: PIOMAS vs CryoSat
« Reply #317 on: October 16, 2019, 07:40:30 PM »
They would make it easier for people if they'd name those sats more creatively.

No one hinders us to nickname them though.

I propose Satty Mc Satface!  8)
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oren

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Re: PIOMAS vs CryoSat
« Reply #318 on: October 17, 2019, 03:04:25 AM »
Trying to visually compare PIOMAS and Cryosat, the correlation is surprisingly good IMHO.
Top thickness is roughly the same, location of thickest ice is roughly the same (shifted to the right in PIOMAS). The hole north of Greenland is roughly there, as well as the thinner ice between the Pole and FJL.
Note the Cryosat data is from a range of dates, I am using PIOMAS from Sept. 30th as a rough equivalent (taken from Wipneus' animation).

Jim Hunt

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Re: PIOMAS vs CryoSat
« Reply #319 on: October 17, 2019, 11:53:56 AM »
Do we have any info if the Polar Science Center are doing comparisons of their model data with CryoSat-2 data?

Yes. See:

https://www.researchgate.net/publication/307429069_Comparison_of_Arctic_Sea_Ice_Thickness_from_Satellites_Aircraft_and_PIOMAS_Data

Quote
In this study, six Arctic sea ice thickness products are compared: the AVHRR Polar Pathfinder-extended (APP-x), ICESat, CryoSat-2, SMOS, NASA IceBridge aircraft flights, and the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS).

There's also this related set of slides:

http://www.wmo.int/pages/prog/sat/meetings/documents/PSTG-6_Doc_06-01-05_SIThickness-Intercomparison-Wang-Key.pdf

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Re: PIOMAS vs CryoSat
« Reply #320 on: October 17, 2019, 01:55:12 PM »
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

Glen Koehler

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Re: PIOMAS vs CryoSat
« Reply #321 on: May 05, 2020, 04:17:06 PM »
     PIOMAS vs. JAXA AMSR2 thickness (vs. Bremen, NSIDC, ASCAT concentration.)
      There seems to significant variation in the different representations of ASI thickness for last week of April among different observation methods.  To my eye, PIOMAS stands out from the rest in that it makes the condition of the ASI look much stronger than the others.  I don't know if the PIOMAS May 1 ice thickness map is a representation of May 1 or the entire month of May.  If the entire month, that would explain some of the difference.

     Not only do the thickness maps vary, but it seems strange to see 2-3 meter thick ice in some images at the same location of well below 100% concentration in other images. 

    Here is a gallery of recent ASIF postings of images showing ASI thickness and concentration

   https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262447.html#msg262447
   PIOMAS false color thickness May 1

   https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262455.html#msg262455
   and https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262475.html#msg262475
JAXA AMSR2 false color thickness April 30  (missing legend)
   Legend at https://ads.nipr.ac.jp/vishop/#/monitor


Concentration
--------
https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262447.html#msg262447
   NSIDC concentration and Bremen false color conc., both April 30, both missing legends.
   NSIDC legend at https://nsidc.org/data/seaice_index/images/n_conc_hires.png
   Bremen legend at https://seaice.uni-bremen.de/sea-ice-concentration/amsre-amsr2/

   https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262582.html#msg262582
ASCAT Oct. 7, 2019 to May 2, 2020.  Missing legend.
   Inscrutable legend at https://manati.star.nesdis.noaa.gov/datasets/ASCATData.php
  You have to use pull-down list for ice images to see the legend.

   https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262507.html#msg262507
   Bremen conc. gray scale, April 26-May 1.  Missing legend.
   Legend at https://forum.arctic-sea-ice.net/index.php/topic,3017.msg261731.html#msg261731
and https://seaice.uni-bremen.de/sea-ice-concentration/amsre-amsr2/


https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262460.html#msg262460
   Bremen conc. false color animation April 20-30.

https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262432.html#msg262432
   Bremen false color conc. with Polarstern location May 1

https://forum.arctic-sea-ice.net/index.php/topic,3017.msg262472.html#msg262472
   Polarstern photo from bridge April 28


----------------------

   Many more with interpretive legends at http://greatwhitecon.info/resources/arctic-sea-ice-graphs/

« Last Edit: May 06, 2020, 01:14:03 AM by Glen Koehler »

oren

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Re: PIOMAS vs CryoSat
« Reply #322 on: May 05, 2020, 06:52:45 PM »
The map Wipneus posted in the PIOMAS thread is for May 1st, and the animation shows progression over the month. Bear in mind the maps show average thickness, while PIOMAS internally models ridging and calculates the concentration in several thickness bins.
The thick ice in the maps near Svalbard is a result of the movement of a large field of ice in March from north of Greenland towards Svalbard, so I expect the high thickness there is real.
« Last Edit: May 05, 2020, 08:47:26 PM by oren »

interstitial

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Re: PIOMAS vs CryoSat
« Reply #323 on: May 05, 2020, 08:42:59 PM »
<snip>
     Not only do the thickness maps vary, but it seems strange to see 2 meter thick ice in some images at same location of well below 100% concentration in other images. 
<snip>
concentration in this instance is a measurement of surface area and does not correlate to thickness or volume in any respect. Specifically it is the fraction of surface area that has ice in it per unit area.

Thickness is a measurement that is perpendicular to the surface area.


In real terms you can have 5m thick ice that only covers 3% of the surface

paolo

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Re: PIOMAS vs CryoSat
« Reply #324 on: May 05, 2020, 09:05:38 PM »
concentration in this instance is a measurement of surface area and does not correlate to thickness or volume in any respect. Specifically it is the fraction of surface area that has ice in it per unit area.
Thickness is a measurement that is perpendicular to the surface area.
In real terms you can have 5m thick ice that only covers 3% of the surface

I can only bounce, thickness + surface area are strictly related to volume!
In your example "In real terms you can have 5m thick ice that only covers 3% of the surface" you have the same volume as 15cm thick ice and 100% surface area.

Glen Koehler

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Re: PIOMAS vs CryoSat
« Reply #325 on: May 05, 2020, 10:50:47 PM »
<snip> concentration in this instance is a measurement of surface area and does not correlate to thickness or volume.

      Thanks interstitial.  Agreed, but it seems to me that where the average ice thickness is 2-3 meters, there would have to be very nearly 100% concentration.  While cracks, leads, and polynyas are certainly possible in 2-3m thick ice, my guess is that there would be only limited expanse of open water adjacent to such thick ice.  So it surprises me to see the same areas categorized as both 2-3 meters thick and far below 100% concentration on essentially the same date. 

      Maybe having thick ice and <100% concentration at the same location is totally congruent.  I'm just a liquid water landlubber trying to make sense of these images. Are these various observations realistic, or is the apparent conflict between thickness and concentration due to different interpretations of readings by different sensors? 

      The variation between estimated thickness by different methods seems to be greater than the variation between different concentration estimates.  Which makes sense because Extent and Area are more directly observable from satellites than thickness.

      For thickness, my guess is that PIOMAS is the most reliable - even though JAXA and alternate version of AMSR2 thickness agree with each other more than either matches PIOMAS.  My preference for concentration is Bremen AMSR2 false-color, or the Bremen animation.  At least those are the easiest for me to interpret. (But I sure do like that ASCAT animation showing drift motion!)  Based on recent comments made on other ASIF threads, I suspect that what looks like open water on the grayscale AMSR2 can be moisture in the air.  The NSIDC concentration image is aesthetically pleasing but more difficult to translate into concentration %.

     My other not-so-subtle point was that images that include the interpretive legend are more useful than images without the legend.
« Last Edit: May 06, 2020, 08:56:06 PM by Glen Koehler »

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Re: PIOMAS vs CryoSat
« Reply #326 on: May 05, 2020, 11:06:32 PM »
I hope this helps

Glen Koehler

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Re: PIOMAS vs CryoSat
« Reply #327 on: May 05, 2020, 11:08:51 PM »
    Thanks uniquorn.  I found that, but I could not deciper what the o-like symbol (which to me means sigma & 1 standard deviation), represents on that scale.  -5 to -30 what? 
« Last Edit: May 07, 2020, 06:30:15 PM by Glen Koehler »

uniquorn

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Re: PIOMAS vs CryoSat
« Reply #328 on: May 05, 2020, 11:15:31 PM »
probably degrees. Off topic and I apologise for attempting to infer thickness from an ASCAT image.

Glen Koehler

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Re: PIOMAS vs CryoSat
« Reply #329 on: May 07, 2020, 08:17:25 PM »
     PIOMAS vs. JAXA AMSR2 thickness (vs. Bremen, NSIDC, ASCAT concentration.)
    In cleaning up the previous message I accidentally replaced the PIOMAS link.  Too much time gone by so now I can't edit that message anymore, but for the historical record here is the correct link to the message showing PIOMAS thickness.  Sorry for my dyslexic typing.
https://forum.arctic-sea-ice.net/index.php/topic,119.msg262853.html#msg262853

     Today's Arctic image of the day (Thanks Espen - btw it looks like they left that door open again!) at https://forum.arctic-sea-ice.net/index.php/topic,416.msg263212.html#msg263212 shows what looks like 100% ice cover at Utqiagvik on May 7. 

     The May 7 Bremen ice concentration map suggest less than 100% cover along most (but not all) of the coast looking west or north from Utqiagvik https://seaice.uni-bremen.de/data/amsr2/today/Arctic_AMSR2_nic.png.  But the Bremen map also shows a thin sightline of 100% ice cover if looking southwest, and it is not very clear in the photo whether there is solid ice or open water offshore. 

     This reminds me of the more definitive photo from the deck of the Polarstern in my earlier post showing solid ice cover even though the sea ice concentration maps for that location on that day indicated concentration well below 100%. 

      My point is not to whine that the ice concentration maps don't match this or that photo, I understand that perfection is impossible.  And I'm old enough in years and young enough at heart to be amazed and appreciative that we get to see any of this stuff (and gloomy enough to brood that good and evil seem to be in a dead heat race towards unwelcome consequences for our actions.  We are just learning the understand the Earth as we trash it.)   

      But I would like to understand what the sea ice concentration maps are measuring and representing.  In at least the Polarstern case, the photo indicates that the sea ice concentration imagery can overestimate the percentage of open water and underestimate the continuity of solid ice cover.  I suspect that at this time of year sensors may interpret superficial surface melt on sea ice as open ocean water.  ASIF posts in other threads have said that is the case for false readings of early melt pond activity, and other posts have noted that moisture in the air can fool sensor readings of ice cover.  Insight on interpreting sea ice concentration images welcomed.
« Last Edit: May 08, 2020, 01:53:36 AM by Glen Koehler »

oren

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Re: PIOMAS vs CryoSat
« Reply #330 on: May 11, 2020, 04:36:10 AM »
From the Polar Science Center monthly update, with a hat-tip to Jim Hunt:
Quote
April  ice thickness anomalies from PIOMAS agree well with the multi-sensor CryoSat/SMOS thickness analysis from the Alfred Wegener Institute/ESA (Fig 7) with the strongest positive and negative anomalies in the right places. An area of thicker than normal ice  north of Greenland that was present in PIOMAS but missing from CryoSat/SMOS in March is now is now showing up in Cryosat/SMOS though considerably smoothed out.   The time series for CryoSat/SMOS  total volume shows  April 2020  a lower relative to the  2011-2020 period while PIOMAS shows a bit of an uptick. Neither time series indicates a trend over the past 10 years contrasting the drastic thinning over the last 40-years.  Note that Cryosat/SMOS retrievals only go through April 15 as the microwave based retrieval of both system forces a summer hiatus.

Paul

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Re: PIOMAS vs CryoSat
« Reply #331 on: May 11, 2020, 07:58:41 PM »
I think some imo are getting confused with thickest ice and the ice anaomolies when looking at those charts. We know in the 2011-2018 period ice in the Barants sea has struggled to grow at times, especially near Svalbard and some of that red may explain that rather than we have super thick ice in that region.

I think the most telling for me both models are showing alot of blue in the ESS and too me looking at worldview, we are seeing that already with open water starting to develop and some of the ice there really does look thin even looking from above.

Glen Koehler

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Re: PIOMAS vs CryoSat
« Reply #332 on: May 11, 2020, 11:59:27 PM »
    Paul is referring to a since-deleted post of mine just above his where I spoke about the thickest ice being on the edge of an impending Fram Strait drainage event.  Then I took the post down, which left his post hanging in mid-air with nothing to refer to.  So here I am back again to correct my attempted correction. 

    I was wrong and Paul is correct that the PIOMAS and Cryosat images show thickness anomalies, not thickness.  That said, the locations with the greatest positive thickness anomalies of > +1 meter are likely to be thick enough to affect Fram export volume if they do indeed get moved out.  What actually happens will presumably show up in the next Wipneus Fram export graph that covers the days this week with observed and forecast high winds.  That's if the wind forecast proves accurate, which seems likely since the strong winds shooting down the Fram still appear in the current forecast update through the end of May 11, all of May 12 and into late May 13 UTC time.
« Last Edit: May 12, 2020, 12:24:16 AM by Glen Koehler »

oren

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Re: PIOMAS vs CryoSat
« Reply #333 on: May 12, 2020, 03:22:40 AM »
I think the anomalies are important in themselves. A lot of the ASI discussion is about comparison between melting seasons. To get to lowest volume for the date, one just needs to get rid of the positive anomalies, rather than of the whole absolute volume.
However, I think this discussion is best continued in the PIOMAS thread and/or in the melting season thread as appropriate. These images were posted here for the comparison between PIOMAS and Cryosat.