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nukefix

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New datasets available over Greenland
« on: April 21, 2015, 01:39:32 PM »
The ESA CCI Ice Sheets Greenland - project has released some data products for download:

http://www.esa-icesheets-cci.org/?q=node/153

The data products include the following parameters:

SEC = Surface Elevation Change
IV = Ice Velocity
CFL = Calving Front Location
GLL = Grounding Line Location

nukefix

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Re: New datasets available over Greenland
« Reply #1 on: April 21, 2015, 02:09:39 PM »
Example of IV

nukefix

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Re: New datasets available over Greenland
« Reply #2 on: April 22, 2015, 12:06:47 PM »
Example of SEC
« Last Edit: April 22, 2015, 12:12:20 PM by nukefix »

nukefix

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Re: New datasets available over Greenland
« Reply #3 on: April 22, 2015, 12:15:13 PM »
Coverage of CFL-product

nukefix

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Re: New datasets available over Greenland
« Reply #4 on: December 17, 2015, 11:04:30 AM »
There has been an update to Greenland products from this project, see:

http://lists.cryolist.org/pipermail/cryolist-cryolist.org/2015-December/000574.html

Looks like most datasets have been updated. The Greenland velocity-mosaic from 2015 is a new addition. Data is available for download from here:

http://products.esa-icesheets-cci.org/


sidd

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Re: New datasets available over Greenland
« Reply #5 on: December 18, 2015, 05:46:57 AM »
Eggzellent. Flow directions is nice to have.

A-Team

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Re: New datasets available over Greenland
« Reply #6 on: December 19, 2015, 06:13:52 PM »
Quote
Flow directions nice to have
Strange site. 1995-96 flow directions on Petermann protected by registration fire wall, just to get beyond a thumbnail?

Now the page below has some fantastic 2015 sentinel speed images and useful comparisons with other different radar satellites. (To get full resolution, click on the thumbnail, then click on bigger image or open in new tab.)

http://www.mdpi.com/2072-4292/7/7/9371/htm

However it doesn't show unit vectors for flow direction nor isotach contours nor link to an underlying file with the grayscale data. Sometimes velocity magnitude is indicated with saturation, direction via the hue circle, and ground topography with the value channel (or similarly in RGB or CIELAB). Are they even determining direction given interferometry only measures line-of-sight displacement?

The animation shows the magnitude of the speed-up over the last five years, using Palsar for 2010. You can see Jakobshavn encrouching  from below on Eqip. However it's all but impossible to quantify the changes because the peculiar color palette isn't separable.
« Last Edit: December 20, 2015, 03:10:45 PM by A-Team »

A-Team

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Re: New datasets available over Greenland
« Reply #7 on: December 20, 2015, 03:11:06 PM »
Elsewhere in western Greenland, the gradient of surface DEM could serve as a proxy for direction of surface ice flow but along the coast the surface topography is pocketed enough to make that unworkable at resolution -- it's better to animate Landsat to see what the ice is really doing (but see another trick for that below).

With 22 years of ice penetrating radar flights covering Greenland, these being the primary experimental data available for bedrock topography, ice depth, paleo, and deformation history, there's a need to associate ice surface velocity to  radar transects. This might be utilized for anisotropic kriging (bedrock smoothed in flow direction), modeling of future flow, or direction of fold developmentin temperate ice.

Flightlines are represented by Cresis as a few dozen high precision lat,lon waystations per 50 km flight segment in kml format (a rigidly formatted txt file carrying a small metadatabase). Needless to say, when the plane changed course, it flew a smooth curve rather than abruptly changing bearing at the joints in line segments defined by the waystations.

Kml files open in the convenient rescalable vector GIS view of the flight in Google Earth. GE also carries with it a Greenland surface DEM of unknown quality relative to what Greenland glaciologists use. GE can plot the slope along any selected portion of the flightline but has no export capability (other than a screenshot, which can be csv'ed in ImageJ).

That's unfortunate as it could have been added across the Cresis data archive. The problem there is that the z coordinate was to zero in all Cresis tracks. Work-arounds can be found using Google search that output the elevations as a csv excel file, eg http://www.geocontext.org/publ/2010/04/profiler/en/ or http://www.gpsvisualizer.com/convert_input or http://freegeographytools.com/2010/online-elevation-profiler

The gradient map of a high quality Greenland surface (or bedrock) DEM could be brought into Google Earth as an image overlay but what is needed is a companion track to each flight line that shows a velocity vector coming off each waystation.

This is not hard to do since for a given waypoint lat,lon it is only necessary to look up the velocity there to get the second point of the new 'path'. It's unfortunate that kml doesn't allow for display of extra vectors. (At some point, ArcGIS or similar proprietary software starts to make more sense.)

The images below show the surface of a deformation region inland from Eqip that is covered by the new Sentinel velocity map in the previous post (which is in polar stereographic rather than GE projection: dgal needed). The purple flight lines come in from the calving front -- there are 4-5 repeat flights from different years because the Operation Icebridge navigator followed a perceived centerline of glacier flow.

The third image shows one of these from 2013, again seeming to spill over into an along-flow bowl. It appears the physical context of this upheaval was grievously mischaracterized in an earlier publication. There are 35 radar tomographic transects of this upheaval dating from 1995 to 2014 that must be evaluated, along with 56 Landsat-8 cloud-free scenes from 2013-15 to determine local ice surface velocity flow and presence of  meltlakes, moulins and streams overhead.
« Last Edit: December 20, 2015, 04:28:09 PM by A-Team »

nukefix

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Re: New datasets available over Greenland
« Reply #8 on: January 26, 2016, 05:50:12 PM »
Here's a large animation of Greenland surface elevation change from altimetry. I took the .png:s from the CCI SEC-product and animated them for fun. I screwed up the numbering a bit, every visible year-number is +1 larger than it should be. In other words, 1993-1997 should be 1992-1996.

There's also in image for 2010-2014 using CryoSat but I didn't include it in the animation.

« Last Edit: January 26, 2016, 05:57:37 PM by nukefix »