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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 575414 times)

Shared Humanity

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #300 on: July 06, 2014, 03:06:13 PM »
Espen....a couple of questions about this retreat.

1) In the next 40 years, should we expect a similar retreat of the glacier up the fjord or might the retreat of the calving face slow down as it moves further into the interior of Greenland.

2) Does it look like the northern calving face has retreated nearly the same distance in this time? Should we expect the retreat of this northern face to continue at this pace?

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #301 on: July 06, 2014, 03:37:25 PM »
Shared H,

We really don't know, if you ask Anthony Watts it is only temporary, if you ask me it will probably drill its way deep into the interior of Greenland.

The northern branch don't have much further potential in my opinion, it might become an ice fall and a new fascinating tourist attraction? 
Have a ice day!

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #302 on: July 06, 2014, 04:23:05 PM »
The Joughin group has described what they consider the physical limits to acceleration of retreat. It has about 80 km of channel to go; they estimate a few decades for that. In other words, not an abrupt collapse a la Antarctic ice sheets.

Nice imagery, Espen. I found some more recent historic images at the Nasa Visualization Lab, 2001-2006, from an unnamed satellite that has 6x the resolution of Modis Terra in a 28º ccw rotation.

The character of glacier flow on the north branch has really changed. Formerly, a lot of moraine material was coming down. There are also various melt lakes and other features on both channels. The last image in the slide show is a murky Modis from 2014.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #303 on: July 06, 2014, 04:29:05 PM »
Hello A-Team the "Calves" also changed characters from before where they were "shipped" away, now they are brutally tumbled around, hopefully no animal activists read this?
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A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #304 on: July 06, 2014, 04:47:06 PM »
"The northern branch might become an ice fall and a new fascinating tourist attraction."

Right now, people mostly go to Epiq calving front where there is a hotel with direct views. For that, you would fly to Ilulissat and take a 5 hour boat. (Be careful landing at that airport because I heard the guy who built it took some shortcuts.)

Seattle to Reykjavik is $1783, 12 hours. Reykjavik to Ilulissat $992 but sold out already for August. The Epiq hotel is something like $225 a night.

However we want to go to the calving front at Jakobshavn Isbrae. That is far too dangerous for chartered boat or kayak, though you could go overland to Swiss Camp from Ilulissat with a pack raft for small crossings.

However web cam A shows this is not really not close enough. I suppose there are helicopter or fixed wing charters. Might be better just stay home and just watch 'Chasing Ice' a few more times.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #305 on: July 06, 2014, 04:49:44 PM »
Be careful A-Team I was was involved in the construction of the airport in Jakobshavn, although in a minor scale!
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Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #306 on: July 06, 2014, 05:06:16 PM »
If you want to watch "Grand Calvings" I suggest Helheim, you can get there from Ammassalik and then cross the fjord and do the "rest" trekking 8)
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VaughnAn

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #307 on: July 07, 2014, 08:17:20 AM »
The disintegration of the 5000 feet deep ice from 1794 to roughly 1850 in what is now Glacier Bay, Alaska appears to be a possible example of how some of the Greenland glaciers could disintegrate:

"In 1794, Joseph Whidbey, master of the Discovery during George Vancouver's 1791-95 expedition, reported that his exploration of this part of the coast was blocked by a wall of 2 miles (3.2 km) width and 1,200 metres (3,900 ft)) thick."

[url]http://en.wikipedia.org/wiki/Glacier_Bay_Basin/]http://en.wikipedia.org/wiki/Glacier_Bay_Basin/

Michael Collier also makes references to Glacier Bay in his book, Sculpted by Ice: Glaciers and the Alaska Landscape.

And from National Geographic:

Scientists call Glacier Bay a living laboratory for the grand processes of glacial retreat.

[url]http://travel.nationalgeographic.com/travel/national-parks/glacier-bay-national-park/]http://travel.nationalgeographic.com/travel/national-parks/glacier-bay-national-park/

Explorers along the coast of Alaska also described "blocks of ice as large as small cities along the southern coast of what is now Alaska in the early 1800s.

It seems to me that there are enough similarities of a number of Greenland Glaciers to the ice sheet that was once in Glacier Bay that we can compare this mini ice sheet disintegration to the potential demise of many Greenland glaciers and the larger Greenland ice sheet itself.
« Last Edit: July 07, 2014, 08:35:05 AM by VaughnAn »

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #308 on: July 07, 2014, 06:04:41 PM »
Very interesting post, VaughnAn, one that makes clear the scale at which melting can occur over a historic time frame.

Glacier Bay is an absolutely awesome place -- we went up there last Sept on the Norwegian Princess. Didn't see any calving in a couple of hours parked in front of the glacier but it was making a lot of growling noises. A few glaciers in the western basin are still in balance because of heavy precip being so close to the north Pacific.

I've been pondering whether there is a significant difference between these mountain glaciers and the Greenland ice sheet where there's no underlying mountain.

Jabkoshavn Isbrae is atypical in that it is the only icestream in Greenland that flows over/in a deep gorge, one that averages 1167 m depth below sea level over its last 30 km, not to mention 402 m of ice thickness above for a total of 1569. (I have these numbers handy from calculating total kinetic energy of the icestream today at the Landsat/bedrock forum.)

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #309 on: July 07, 2014, 07:34:42 PM »
I believe we have some more calvings since July 3 (last Landsat update), this time in the southern branch, but it is unclear whether the northern branchs eastern wall is collapsing?

Please click on image to start animation!

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Rubikscube

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #310 on: July 07, 2014, 07:37:24 PM »
I absolutely do not believe this is an emerging nunatak.

I would actually disagree to some extent, and it looks to me as though there is a mountain reaching about 1000 meters above sea level that is the reason, or some of the reason, to why there exists such a melt lake. It also seems that any further development in this part of Jakobshavn will take place in the western areas, which have seen some calvings this year. I have attached my analysis of the northern branch using the same wonderful topography maps as SH at a dangerously high zoom.

Regarding the Zachariae vs Jakobshavn discussion launched by Espen some weeks ago, I would consider Jakobshavn the glacier with the highest volume potential in the very long run. The reasons for that include that the vast network of narrow fjords and overdeepenings that seems to be part of the Jakobshavn system is draining a part of the GIS with significantly thicker ice as well as an apparent lack of fjords connecting Zachariae to the interior of Greenland. That said, Zachariae might have the biggest short term potential, even though I feel pretty confident that volume loss from Jakobshavn will keep increasing.
« Last Edit: July 07, 2014, 09:04:50 PM by Rubikscube »

VaughnAn

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #311 on: July 07, 2014, 08:52:47 PM »
A-Team, I have been to glacier bay too...about 15 years ago...awesome place and did see a couple calvings big enough to rock the ship.

One of the things that came out of all this was that from 1794 and into the early 1800s the ice sheet in glacier bay receded 42 miles even though it was about a mile thick.  It has since receded about another 23 miles to where it is today. I have not been able to find a specific time frame for the recession for the first 42 miles other than it occurred mostly over a period as short as 10 or 20 years.  The tone of anything about this is that one day things were intact and a short time later much of the ice was gone. 


Another important part of this breakup appears to be the size of the icebergs calved.  There are iceberg scrape channels cut through the underwater terminal moraine when large icebergs were pushed out of the bay by the ice disintegrating behind them.

The amount of information about this seems limited but John Muir documented the condition of the flora around the bay in the late 1800s which is consistent with a sudden demise of the lions share of the ice at first then a more protracted demise after that.


[url]http://www.nps.gov/glba/historyculture/john-muir.htm]http://www.nps.gov/glba/historyculture/john-muir.htm

IMHO, this event is a fairly good predictor of the fortunes of a fair number of Greenland's glaciers.  Sure we have models, data, and evidence for and in Greenland itself but Glacier Bay appears to be the only place humans have witnessed an event on a scale large enough to be a fairly valid example of what is to come in Greenland.


VaughnAn

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #312 on: July 07, 2014, 08:55:52 PM »

CraigsIsland

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #313 on: July 07, 2014, 08:56:21 PM »
I've been interested in looking at how much acceleration could be caused a number of variables. One of the variables I look at is just reflectivity/albedo in the area. 2014 albedo is currently tracking just above 2012 values for a certain higher elevation dataset- according to Dr. Box at the Dark Snow Project site: http://darksnowproject.org/.


Here is the Worldview map of the Jakobshavn area: https://earthdata.nasa.gov/labs/worldview/?switch=arctic&products=baselayers,!MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor&time=2013-06-05&map=-2048000,,,-1024000

Compare 7 July 2014 with 2013 and find a clear view of 2012 around the same day. Of note is the reflectivity around the Calving areas up to 20-50 miles out. Not just the melting ponds, but the amount of darker materials clearly present as a differential and is visible at the 250m resolution on MODIS.

It's amazing to see the changes in a short amount of time. I would be surprised if the GIS as a whole had a blockbuster 2012 like melting percentage that was close to/at 100%. But that's not what I'm concerned about; it's the amount of time that albedo gets exposed to higher temperatures/sunlight for a longer period of time. At the minimum, I see a acceleration of the historical trajectory of calving events.

The following is a lot of amateur presumption and is no way accurate lol:  Since Jacob has that remarkable depth (which could be heated by geothermal properties) beyond the current grounding, I wouldn't be surprised to see a massive event that destabilizes the GIS. Think of it as a sort of canal system where a boat gets lowered into a shallower bit of sea.

thoughts? just say "No" if it's just ridiculous and I'm missing some basic science fundamental. Or inform me. Either way - appreciate it.

The Zach vs. Jacob is  a very interesting dynamic to discuss (and frame for others) on and I'd like to thank those involved in that.

Steve Bloom

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #314 on: July 07, 2014, 09:27:41 PM »
VaughnAn, are you aware of any paper(s) on the Glacier Bay collapse of ~200 years ago?

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #315 on: July 07, 2014, 11:59:52 PM »
Calving looks dramatic, Espen ... the Landsat schedule is shown below, unfortunately the next high resolution image is not due until July 10.

I located the experimental data on temperature profile down the bore holes -- quite interesting. There's been more recent followup on the significance of bottom 'temperate ice' (near melting point) and its effect on creep: surprisingly, not that much.

http://php.scripts.psu.edu/staff/d/j/djl22/GSTREAM/JG2002Luethi.pdf
http://students.washington.edu/kpoinar/Presentations/AGUposter_kpoinar_2010.pdf

VaughnAn

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #316 on: July 08, 2014, 02:04:18 AM »
Steve Bloom,

I have seen no papers.  The information available seems difficult to come by.  I have searched the internet for historical records and have found a few in the past but I have not been able to find them now.  There is a book by John Muir, Travels in Alaska but I do not own a copy.  There seems to be only bits and pieces of information between 1794 and the mid 1800s available.  What is clear is that the ice was there in 1794 when Captain Vancouver visited the area and the it was gone not very many years later.

The Tlingit people who lived in the area had an oral history of the area at the time which is mentioned on the National Park Service website link in my earlier post.

TerryM

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #317 on: July 08, 2014, 08:35:30 PM »
It's been ~45 years since I was on Glacier Bay. I'm sure much has been lost since then though I agree that the big losses took place over a very short period.
If records exist of the crash is it possible that they are hidden away in Russia?
Terry

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #318 on: July 09, 2014, 01:43:49 AM »
This is a very fine hand-held from an airplane, maybe IceBridge, on an unknown late summer date. It looks just east upstream on the south branch of the calving front of Jakobshavn Isbrae at the Big Curve. This is some seriously jumbled ice -- we have to applaud the Swiss for venturing out there to drill holes for temperature profiles and bedrock hydraulic connectivity.

The insets in lower left show rendered bedrock DEM under the photo and (logarithmic) ice stream velocities of 2008. The scripts for making these yourself are given over on the Landsat/bedrock forum. The right is a tweaked July 2014 overhead Landsat.

JayW

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #319 on: July 09, 2014, 01:45:22 AM »
Steve Bloom,

I have seen no papers.  The information available seems difficult to come by.  I have searched the internet for historical records and have found a few in the past but I have not been able to find them now.  There is a book by John Muir, Travels in Alaska but I do not own a copy.  There seems to be only bits and pieces of information between 1794 and the mid 1800s available.  What is clear is that the ice was there in 1794 when Captain Vancouver visited the area and the it was gone not very many years later.

The Tlingit people who lived in the area had an oral history of the area at the time which is mentioned on the National Park Service website link in my earlier post.

Here is a paper on glacier bay leading up to 1794, but it doesn't really discuss the retreat following the rapid advance.  Suppose this is going OT, feel free to move my post to the glaciers thread. :)
Link courtesy of Alaska.edu http://uas.alaska.edu/arts_sciences/naturalsciences/envs/faculty_staff/pubs/connor_gbay_holocene_2009.pdf
Abstract
The Neoglacial landscape of the Huna Tlingit homeland in Glacier Bay is recreated through new interpretations of the lower Bay's fjordal geomorphology, late Quaternary geology and its ethnographic landscape. Geological interpretation is enhanced by 38 radiocarbon dates compiled from published and unpublished sources, as well as 15 newly dated samples. Neoglacial changes in ice positions, outwash and lake extents are reconstructed for c. 5500―200 cal. yr ago, and portrayed as a set of three landscapes at 1600―1000, 500-300 and 300―200 cal. yr ago. This history reveals episodic ice advance towards the Bay mouth, transforming it from a fjordal seascape into a terrestrial environment dominated by glacier outwash sediments and ice-marginal lake features. This extensive outwash plain was building in lower Glacier Bay by at least 1600 cal. yr ago, and had filled the lower bay by 500 cal. yr ago. The geologic landscape evokes the human-described landscape found in the ethnographic literature. Neoglacial climate and landscape dynamism created difficult but endurable environmental conditions for the Huna Tlingit people living there. Choosing to cope with environmental hardship was perhaps preferable to the more severely deteriorating conditions outside of the Bay as well as conflicts with competing groups. The central portion of the outwash plain persisted until it was overridden by ice moving into Icy Strait between AD 1724―1794. This final ice advance was very abrupt after a prolonged still-stand, evicting the Huna Tlingit from their Glacier Bay homeland.

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A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #320 on: July 09, 2014, 11:05:31 PM »
As we brace for tomorrow's hi-res Landsat (which might not be online until Friday -- and even then might be clouded over), we might set some rules governing 'records'.

It is not enough for the calving line to retreat past the all-time record set on 20 Sep 13. Although mildly remarkable with 70 more days to go in the retreat season, just going slightly beyond last year is not even keeping up with the multi-year trend: an additional km of retreat is the new normal.

Indeed, slightly more would still be business as usual since the rate of retreat may be accelerating. Thus we shouldn't trouble our colleagues on the ASIB with news on this little glacier until the retreat is a second km beyond the first km expected.

Determining the pixel scale on Fig.3 of Joachin 2014 as 23.3 px per km, measuring peak retreats, and finding the increments gives, noting a measurement error of 1 pixel amounts to 35 m:

Since color Landsat is 30m per pixel as it comes (caution: Espen uses a rougher scale), I've moved the goal line to the 1 (yellow) and 2 km (red) distances from the lines of retreat for 03 Jul 14 (image) and 20 Sep 13 (blue).

Neven

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #321 on: July 09, 2014, 11:16:07 PM »
As we brace for tomorrow's hi-res Landsat (which might not be online until Friday -- and even then might be clouded over), we might set some rules governing 'records'.

It is not enough for the calving line to retreat past the all-time record set on 20 Sep 13. Although mildly remarkable with 70 more days to go in the retreat season, just going slightly beyond last year is not even keeping up with the multi-year trend: an additional km of retreat is the new normal.

Indeed, slightly more would still be business as usual since the rate of retreat may be accelerating. Thus we shouldn't trouble our colleagues on the ASIB with news on this little glacier until the retreat is a second km beyond the first km expected.

Noted.  :)
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Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #322 on: July 10, 2014, 06:03:49 AM »
Yes it is hard to measure a 100 m dash on a moving surface ;)
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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #323 on: July 10, 2014, 04:56:05 PM »
"hard to measure a 100 m dash on a moving surface"

Right. The relationship between the volume of ice discharged (contribution to sea level rise), position of the calving front, glacier movement and terminus thinning is far from simple. For example, if the velocity of the glacier happened to exactly match the rate of calving, the front would be stationary yet record amounts of ice might calve into the fjord.

The first image below paces off 1 km steps along the main ice stream and shows how the July 2013 velocity spead up towards the terminus. This glacier moves so fast that ice 12 ticks out the blue line will be all calved off within a year.

I sought to find markers on the Landsat time series to see how fast the icestream is moving this year. However it is fairly featureless at 15-30 m resolution so not feasible to measure marker movement. This is a job for Digiglobe imagery -- the zoom from 30 m to google map resolution (24 Jun 12 photo) shows what we are missing.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #324 on: July 11, 2014, 01:46:45 AM »
The two expected Landsats came in today, LC80100112014191LGN00, a mostly clear path 10, row 11 and
LC80832332014191LGN00, a path 83, row 233 totally obscured by pretty clouds.

We last had a clear 10,11 on 08 Jun 14 if you are trying to do something along photogrammetric lines. the lat,lon photo centers are 69.60648, -50.86015 and 69.6066,-50.86458 respectively, so very favorable geometrically as those numbers correspond to a nadir displacement of 172 m http://www8.nau.edu/cvm/latlongdist.html

The slides compare the 10 July 14 calving front with 03 Jul 14 (LC80 09 011 2014184LGN00). Both are processed up through cropping and contrast normalization in ImageJ as 16 bit Tiffs, then exported to Gimp for alignment and resolution bumping from 15 m to 7.5 m using Lancsoz3 (sinc).

Note the strong surge of the ice stream -- faster than calving front retreat this week -- moving it 315 m further out in the fjord. Note the sharp shear line in the lower left. The giant iceberg in the upper left is just over a km in width -- this is a good photo pair for measuring berg displacements.

Click on image if it doesn't animate

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #325 on: July 11, 2014, 04:25:09 PM »
A-Team, that shows Modis is very unreliable to use as documentation.

It is "What you see, is not what you get" (Wysinwyg).
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A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #326 on: July 11, 2014, 05:32:34 PM »
Yes, clouds can look so much like calving front, it takes two very clear days to compare Modis. 250 m vs 15 m resolution means 16.7 pixels in Landsat for the 1 in Modis. Still, it gives a heads-up in most cases. However even with Landsat, it is a struggle to measure ice stream velocities.

It appears that 10 July - 03 July is a pure surge situation, no calving. The same bergs can be seen in both. That provides an opportunity to compare the positional shift of micro-feature pairs.

The largest reliable pixel-pair movement I found was 43 pixels at 7.5 m resolution or 322.5 meters in 7.004 days (subtracting the SCENE_CENTER_TIME time stamps in the metadata files MTL.txt). That works out to 46.1 m per day or
16.8 km per year which is a near-record surge velocity. However, upstream values were less and somewhat variable.

We have an ~ stereo pair of Landsats coming in tomorrow 8,11 and 8,12. Might give us a better sense of the surface, depending on sun heights, azimuths and time differences. The 10 July was SUN_ELEVATION = 42.6, SUN_AZIMUTH = 173.0.

With better imagery, Joachin 2014 did this much more accurately as far as 37 km (M43 in their coords) up the south branch for 2009-13. They see unmistakable acceleration as far as as 20 km from the calving front (M26).

Various explanations have been put forward but I expect the physics here to be resolved by September (which will trickle down to us via a Feb 2015 journal article). That will allow future discharge of Jakobshavn Isbrae to be modeled better than today.

However that model won't be applicable to any other glacier in Greenland as the others lack the overdeepened bed channel. In some ways, GRACE trending (mass balance from gravity) may provide the best overall view of Greenland's total contribution to sea level rise.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #327 on: July 12, 2014, 05:26:38 PM »
The two animations below illustrate (imperfectly) certain aspects of surface ice flow on Jakobshavn Isbrae.

The first imagines lines of red and yellow traffic cones laid out in 20 lines perpendicular to main channel by an unpaid intern. These lines progress over a calendar year towards the calving front in proportion to the velocity of their spot.

The velocity increases monotonically closer to the calving front, so from the perspective of a line (lagrangian coords), the faster ones in front are getting farther away whereas the slower ones upstream are falling farther back. The animation does capture that but not very noticeably.

The second animation is similar but also displays the effect of slow-down along the edges. This has the effect of making an initial line of ice more and more convex over time because its center moves more rapidly. The motion illustrated is only heuristic -- not tied quantitatively to the actual data of Joachin et al -- though I did bake in some acceleration using milliseconds of frame delay.

Neither animation captures the seasonality of motion nor the year-to-year acceleration of this motion. While the glacier is fast throughout the year, it moves even faster during the summer months. It would be possible to display the motion accurately but not by the methods I have been using.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #328 on: July 12, 2014, 06:19:40 PM »
Great work A-Team and very illustrating.
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A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #329 on: July 13, 2014, 02:39:07 AM »
Most unexpectedly, LC80 81 233 2014 192 LGN00_B8 arrived today at EarthExplorer -- and it is a crisp cloud-free beauty. We have not seen anything from satellite path 81 before.

Perhaps the reason is Jakobshavn is usually in the dark at the time of flyover; this photo was taken close to midnight (23:53:59) with the sun only 8.4º above the horizon at an azimuth of -46.8º (ccw from due north).

The illumination gives fantastic shadow relief to an otherwise flat landscape. In fact, with a cosine or two, you could figure out surface heights at the edge of the north channel (which is really an icefall at this point; its depression is more like a tarn than a melt lake).

There has been some calving along the NE edge of the front and it looks like this will continue. I won't belabor the comparison to earlier dates since we just did that yesterday for the 10 July and earlier images. To spare people the gigabyte download and 16 bit processing, I have attached the calving front from the 15 m panchromatic.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #330 on: July 13, 2014, 03:02:24 AM »
Here is the shadow situation on the north branch. It sheds light on the melt lake/tarn/nunatak feature we discussed previously.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #331 on: July 14, 2014, 01:17:36 AM »
"It doesn't get any better than this" --  the guys are running low at beer camp but just then the swedish bikini team drops by.

Oh yes it does, a lot better. Despite an incomprehensible file navigation system, I eventually stumbled across the Cresis folder containing the P3 radar echoes overflights of Jakobshavn Isbrae for 04 Apr 13. And, make my day, they allowed anonymous guest/password ftp download (201 files).

ftp://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130404_02/

The map in the upper right shows the flight lines: 6-7 transects plus one straight up the channel! These flight lines are also provided as a satellite image overlay.

The flight lines are slightly kattywumpus (not perpendicular to flow lines) so rotation and rescaling of the sat photo is necessary to see what the echogram refers to on the ground (though it also gives coords). The dotted orange rectangle shows this correspondence more or less worked out for the one I tried.

Cresis provides both a raw radar return and an annotated version called echo_picks where someone competent to interpret the data has colored in certain boundary lines. (Actually there is phenomenal software that can do this; I took a pass at this myself with PovRay relief, bottom.)

The example below has two such lines (purple and red) plus an intermediate line that for some unexplained reason is not deemed of interest. I'm guessing that the lines show the ice surface (omitting snow cover), water pockets, a Wisconsonan/Holocene transition, temperate ice, bedrock and side scatter from hills and walls.

The stratifications are rather minimal compared to the deformation drama up at Petermann. However the radar return is measuring dielectric permittivity which can amount to water content which can amount to critical rheological properties of intermediate ice filling the Jabobshavn channel.

So if you came for the bedrock, stay for the stratifications. They provide the natural coordinate system for any serious modeling of this glacier's behavior.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #332 on: July 14, 2014, 05:33:10 AM »
A-Team you are really digging into those hidden x-files? Did you stumble over the Swedish Bikini team too? ;)
Have a ice day!

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #333 on: July 14, 2014, 05:14:45 PM »
Not yet, Espen. I'm hoping to get more people engaged in these files now that the football tournament is over (though there is always some other sport to replace it).

I'll post a couple rounds of Cresis profile analysis specific to Jakobshavn Isbrae here but if there's interest, start a separate forum section for ice-penetrating radar, a huge deal in Greenland and Antarctic and critical to Arctic Ocean ice thickness measurement validation (ie volume).

These profiles, in my view, are seriously under-interpreted and in some cases like Petermann Glacier, demonstrably mis-interpreted. The intermediate stratifications and their deformation are exceedingly important to ice sheet history and flow properties; it is not enough simply to read off surface elevations and bedrock depths if the goal is estimating future sea level rise attributable to Greenland by prioritizing to the fastest marine outlet glaciers.

After visiting numerous dead '404' urls, I did eventually find a 'FAQ' among the read-me Cresis files. It did not have any examples of annotated profile features but did explain their rather redundant data storage system and contained some interesting factoids about ice-penetrating radar.

<url>ftp://data.cresis.ku.edu/data/rds/rds_readme.pdf</url>

The first thing to understand is Cresis uses MatLab formats but you probably do not: $2250 per individual license, $149 for home. The home use license does not include government, academic, commercial, or other organizational use (blog?).

There'd be a learning curve: "MATLAB is a high-level language and interactive environment for numerical computation, visualization, and programming. Using MATLAB, you can analyze data, develop algorithms, and create models and applications." <url>http://www.mathworks.com/products/matlab/</url>

However, the data is also available as desktop-readable triples of track location maps (file names ending in _0maps.jpg), radar return profiles (_1echo.jpg), and interpreted tracks (_2echo_picks.jpg). The latter are 'manually driven processes' where a trained individual marks up surface and bottom reflections with purple and red lines respectively. (However bedrock cannot always be located for the Jakobshavn gorge.)

Those depths are captured into excel-readable cvs numerical format. Of the 9 columns, 5 are useful (lat, lon, surface, bottom, elevation), 1 is easily derived (thick = surface - bottom), and 4 can be deleted. Cresis data is carried to excessive precision -- surely the bedrock is not really measured to centimeter accuracy as numbers like 2087.12 suggest. And surely latitude is not usefully measured to 6 decimal points (0.11 m) when profiles show 5 m precision (see below and <url>https://gis.stackexchange.com/questions/8650/how-to-measure-the-accuracy-of-latitude-and-longitude</url>

The 15 years of flight have generated a lot of files. After drilling down to Greenland, look for the Jakobshavn Isbrae specific folders such as 09_01 (transects) and 09_02 (tracks along the icestream) for the given date, here Apr 14. Each profile covers 50 km, so just two profiles suffice for the Jakobshavn gorge.

The internal dimension of profile jpegs is 931 x 734 pixels (in the example examined). The width is variable but for a 49.91 km transect, the 1 x 734 vertical slices are spaced at 53.6 meters which represents a resolution of 75 points to characterize bedrock topography for a 4 km wide gorge. A buried nunatak or pothole of smaller dimension might still be recognized by combining data from different years as the bedrock doesn't change year to year and the flight lines would be slightly different.

The depth is not measured directly but rather return time of a radar pulse (microseconds of propagation delay). Under the assumption of 3.15 dielectric  for ice -- not applicable to snow, firn, englacial pockets, or wet temperate ice -- the depth is then calculated using the speed of electromagnetic radiation in a medium of refractive index sq rt (3.15), or 168,913,914 m/s instead of the usual 299,792,458 m/s.

The depth scale range has to vary from scene to scene to accommodate top elevation and bedrock depth. In the example I looked at, 2000 vertical meters was represented by 369 pixels for a resolution of 5.4 meters. This scale seems to be consistent, only modified by offsets.

Cresis also offers kml (Google Earth) files for the track segments. I found these convenient for precisely co-registering track profiles via their lat,lon coordinates to Landsat images. Simply mouse along the track to find the exact lat,lon of a radar reflection column. This is otherwise problematic because the icestream channel curves quite a bit. I found a way to lay down a precise grid in Gimp and will post that shortly.

For the two along-gorge, west to east flight lines of April 2014 (which may overlap slightly rather than butt up end-to-front), go to ftp://data.cresis.ku.edu/data/rds/, open 2014_Greenland_P3/images_csarp-combined/ and append:

20140409_02/20140409_02_004_0maps.jpg
20140409_02/20140409_02_004_1echo.jpg
20140409_02/20140409_02_004_2echo_picks.jpg

20140409_02/20140409_02_005_0maps.jpg
20140409_02/20140409_02_005_1echo.jpg
20140409_02/20140409_02_005_2echo_picks.jpg

For the seven cross-gorge transects (some require a north/south pair) in west to east order of April 2014, append:

20140409_01/20140409_01_022_0maps.jpg N
20140409_01/20140409_01_021_0maps.jpg S
20140409_01/20140409_01_019_0maps.jpg
20140409_01/20140409_01_017_0maps.jpg N
20140409_01/20140409_01_016_0maps.jpg S
20140409_01/20140409_01_014_0maps.jpg
20140409_01/20140409_01_012_0maps.jpg N
20140409_01/20140409_01_011_0maps.jpg S
20140409_01/20140409_01_009_0maps.jpg
20140409_01/20140409_01_006_0maps.jpg

The data go back quite a few years (to 1993 for Jakobshavn) and involve other aircraft and other radars. It is not trivial to commingle older with newer data but there may be some value to it.

I've attached the 2014 flight line that goes under the calving front -- note the intriguing structure approximately at the first sill.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #334 on: July 14, 2014, 10:31:45 PM »
""I'm hoping to get more people engaged in these files now that the football tournament is over (though there is always some other sport to replace it).""


A-Team I understand your frustrations, it would be nice to see you and other capable people work together and get some of the many results I expect are hidden in the those files!
Have a ice day!

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #335 on: July 15, 2014, 06:36:51 PM »
Here is the latitude, longitude grid for the area at 30 m resolution in Landsat-8 projection. This is necessary in order to accurately geo-locate ice penetrating radar transects and up-channel flight tracks. I'll post the 15 m channel-only coords over on the Landsat/bedrock forum.

There is plenty of opportunity for error in doing this so the first image outlines how this is done -- pick two fixed rocks whose coordinates can be accurately determined from google earth's very high resolution digiglobe photo. These rocks must also have good vertical and horizontal separation.

Next, choose a grid cell that has easy-to-remember digital lat,lon coordinates and grid spacing favorable to the overall map scale. Note the latitude increments by 0.01 abut the longitude by 0.02. These can be converted into x,y pixel coordinates by considerations of proportionality. The grid itself is drawn in gimp using a deeply buried command, Filters -> Render -> Pattern -> Grid.

Next up: geo-locate some Cresis stratification profiles on our preferred surface imagery and bedrock DEM.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #336 on: July 16, 2014, 04:29:37 AM »
Isostatic rebound comes up on the forum from time to time; I came across this recent account specific to the south branch of Jakobshavn Isbrae. The figure shows glacial thinning (Hoehenrate) is on the order of -5 m per year whereas mantle rebound is less than 20 mm per year, centered of course right under the area of mass balance loss. That's a factor of 250.

Upper left shows glacial velocity near the calving front in 2010 was markedly slower towards the sides but pushing 50 m/day towards the center. Upper right shows the region lifted up by tides; at that time, the glacier had a floating tongue.

http://public.beuth-hochschule.de/~korth/GROENLAND/Texte/zfv_2013_1_Dietrich_et-al.pdf

I also found some excellent videos of the fjord and calving front -- take the helicopter tour to save yourself a bucketful of euros:

August, 2012 Jakobshavn calving event (different  from Chasing Ice)


‪Helikoptertur fra Sermeq Kujalleq til Illulissat‬


‪Jakobshavn Glacier POV Helicopter Ride‬

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #337 on: July 16, 2014, 03:03:26 PM »
However that model won't be applicable to any other glacier in Greenland as the others lack the overdeepened bed channel. In some ways, GRACE trending (mass balance from gravity) may provide the best overall view of Greenland's total contribution to sea level rise.
Repeat-pass altimetry provides a much higher resolution and reaches pretty close to the margin, so I'd combine the two.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #338 on: July 16, 2014, 07:32:04 PM »
The Grace satellite pair is way beyond its design lifetime and had a power outage for a chunk of last summer. Some say they are flying too high for ideal resolution at the scale of Greenland but that Goce can fix that (after a couple more years of data).

Those altimeter measurements are useful for sure. But what exactly are they measuring, surface height of the snow? That would be problematic for mass balance, because the density profile of snow through firn to ice needs to be known. This density could vary significantly depending on depositional and compaction history and water content from melt or rain-on-snow events. Modelling it however might reduce the error to insignificance.

Maps like the one above go beyond determination of overall Greenland mass balance loss -- they seek
to map where that is occurring. That is not needed for sea level rise contribution.

Errors in localization have recently been refined by replacing Grace spherical harmonics expansion to order 60 with Slepian functions. I reviewed this somewhere on the ASIF last year, proposing cylindrical coords for Greenland plus  cylindrical Slepians, the counterpart to Bessel functions, to maybe refine mapping resolution.

That Dec 2012 PNAS paper has free access. I have not had a chance to follow up on the 12 subsequent articles that cite it. In terms of extrapolating mass loss forward in time, that could be done by simple-minded trending or by separately modelling identified main contributors such as Jakobshavn and 3-4 others.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3523835/

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #339 on: July 17, 2014, 12:27:14 AM »
Anyone see any interferometric SAR images on the internet for Jakobshavn? Or for that matter any ESA Sentinel-1 radar images besides the one we have for Epiq?

They have fringes like the one for Petermann glacier below. To some extent on Jakobshavn, the neighboring ice sheet has been entrained by the main high velocity icestream. The crevasse fields (second image, wavelet transform) indicate strain to the extent they depart from gravitational flow (orthogonality to DEM contours). Note SAR velocity fields are projected onto the x,y plane whereas actual movement includes a vertical (z) component.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #340 on: July 17, 2014, 04:37:04 PM »
Three new Landsat images were just posted. I'm not sure what caused the five day holdup on the 12 July pair nor for that matter why the 17 July arrived on 17 July. It takes a while to download these giant packages and process them into 8 bit but I have high hopes that something interesting can be done with the near-simultaneous stereo pair. If not, ponder why annual net calving front retreat ~1 km is slightly less than annual glacial advance ~12 km.

Scene   #Day   Day   Mon   Year   Path   Row   Clarity

LC80842322014198LGN00   198   17   Jul   14   84   232   dark + cutoff
LC80080122014193LGN01   193   12   Jul   14   8   12   excellent
LC80080112014193LGN01   193   12   Jul   14   8   11   excellent

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #341 on: July 17, 2014, 07:27:04 PM »
A-Team those July 17 images do not include the calving zone?
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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #342 on: July 17, 2014, 09:59:14 PM »
Yes and no. LC80 84 232 2014198LGN00 normally contains an oblique slice of about the SW third of the calving front, not enough really. It's obscured by clouds anyway. It looks to me like the next Landsats are not due until July 24 and July 26th (two). Modis has some clear recent days and is not showing anything dramatic.

It looks like NASA/USGS had some colossal processing pipeline error, possibly involving many terabytes of imagery that had to be re-worked, hence the weeklong snafu.

One of the images today from 11 July had to be rotated 5.6º, probably a sign that it is still in stereographic pj rather than UTM W zone 22. I will write them to get this fixed.

From the metadata files, it appears that path 8, row 11 and path 8, row 12 are taken a mere 24 seconds apart (center of scene time). From the lat,lon distance calculation on the nadirs, the satellite had moved 162 km over the ground. It is 709 km up. A hasty calculation,  2DEGREES(ASIN(82/709)) in the flat earth approximation gives an angular separation of 13.3º for stereo viewing. However there's very little relief on that landscape.

 

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #343 on: July 18, 2014, 12:22:23 AM »
A-Team, I'd been wondering about the reconciliation of GRACE and GOCE data as a general matter, but note that GOCE was toast as of last November.  I'll check for any recent pubs and maybe also ask Dumb Scientist about it.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #344 on: July 18, 2014, 01:41:37 AM »
Steve,

I got this from an open access article in J. Geod. Sci. 2014; 4:8–18 DOI 10.2478/jogs-2014-0001
M. Herceg, C. C. Tscherning, and J. F. Levinsen
Sensitivity of Goce gradients on Greenland mass variation and changes in ice topography

"...Establishing the presence of an acceleration on the order of magnitude found in the Greenland Ice Sheet requires more than 5 years of data, and we find that the GRACE time series available are now long enough to establish the presence of such an acceleration. Maximally four years of reprocessed GOCE gradient observations will to be available by mid-2014, which may add the supplement GRACE derived solution for mass changes..."

"...The largest accelerations have been observed by the Helheim glacier, Kangerdlugssuaq and Jakobshavn Isbræ"

"...There is hope for future GOCE data acquisitions to be able to further our understanding of mass changes using gravity gradients and gradient anomalies. We expect maximally four years of GOCE gradient observations to be available at the middle of 2014. Furthermore, lowering of the GOCE satellite down to an orbit of 235 km will increase the accuracy and spatial resolution of the measurements. This may then lead to the accuracy needed in order to ob- serve ice mass changes using the GOCE gravity gradients."

"A new GOCE-type mission, with improved accuracy, will undoubtedly provide the possibility to detect areas of mass gain or losses over short time periods."

Sounds like a 'new' mission would indeed be needed if the old one went kaput before mission accomplished.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #345 on: July 18, 2014, 04:06:01 PM »
I looked further into the Jakobshavn Isbrae upchannel P3 flight track of 2014. The primary purpose may have been to measure ice surface for purposes of determining thinning relative to previous years; the particular radar configuration did not seem to detect the bedrock layer (or at least that was not 'picked' as it was in other series).

The data comes in the form of an overview map at three levels of resolution, the ice-penetrating radar scan itself with and without a dashed purple surface line, an excel-type file that has elevations for the surface (and mysteriously for bedrock) and so a column for total ice thickness, and a kml file that overlays the track on Google Earth satellite imagery of Nov 2010.

I sought to tile consecutive segments of the flight path. Each segment covers 50 km so only two were needed to get 100 km up the channel (in curved channel coordinates). I soon discovered the radar scans did not use the same vertical scale. Neither did the flight line depictions, which ill-advisedly used a poor quality satellite image from the 1990's at too low a scale.

The image below has rescaled all this to match plus patched in yesterday's Landsat under the flight path and brought way down to 700 px width to fit on this page. The correspondence is not perfect because of the difficulty in stretching the satellite imagery out to linearize the track -- though this can be done in gimp using a piecewise linear cage transform using the 1 km mileposts I marked out in an earlier image.

The alternative is to use the lat,lon scale (which is not flat, as a coord system for the globe) but as noted above Landsat imagery uses mercator UTM zone 22 W meters which conveniently scale to 15 or 30 m Landsat pixels.

The ice-penetrating radar shows some deeper structures just beyond the calving front and stratification layers below the ice surface way upchannel that probably continue to the summit ridge (and probably improve along the way). I have not yet located the flight scenes that would allow tiling to the summit.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #346 on: July 19, 2014, 02:08:53 AM »
The red path in the first image follows a glacier flowline. Most published data on Jakobshavn Isbrae uses distances measured along such a path as coordinate system. It takes something to get a glacier to deviate from straight line flow so unsurprisingly this path can be described quite well with a small number (8) straight segments over ~100 km.

The second image 'straightens out' the ice stream. I did this by placing vertical guides at the breakpoints, using the guillotine command in Gimp to get 8 image pieces, sheared each separately in the vertical direction until the red line was horizontal, joined the pieces aligning to the red segments, and then rescaled by the ratio of total segment length to width of a horizontal line in the original. The blue line still carries the original channel contour, just inverted.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #347 on: July 19, 2014, 04:17:34 PM »
Land of the midnight sun ... an unexpected but most welcome midnight Landsat image of the calving front in action. It has been 8-9 days since we last got a good look at it.

LC80822332014200LGN00 19 July 14
Path,row = 82,233  Band 8 at 7.5 m
Cloud Cover = 4.9%
Sun Azimuth = -47.3
Sun Elevation = 7.4
Local Time = 00:00:11

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #348 on: July 19, 2014, 04:32:35 PM »
Same Landsat image, north branch. These low angle scenes provide good shadows. This is more of a cliff-hanger ice sheet situation than icestream. The tarn we discussed above is not much of a lake at this resolution. I am not seeing any exposed rock in center scene; though something is causing the large dimple just NE of the tarn, it could be at considerable depth. We may find out this season.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #349 on: July 19, 2014, 05:25:16 PM »
A-Team, nice shot! I wonder what is the height of that cliff? It must be far above the average around the calving area?
Have a ice day!