GLIMS Update: GLIMS ASTER image coverage and research documentation

Mon May 25 21:41:22 MDT 2009

David,
There are indeed lots of usable images for Alaska, and most areas have at least one repeat of usable images over the lifetime of ASTER.  However, it goes downhill from there if you want to do more than what you have done with the images, because the majority of the acquired images are not with GLIMS gains (saturated bands 1 and 2 and often widespread saturation also in band 3), have high-altitude cirrus or smoke haze, or other problems.  If you want to do more detailed classification work (needed for instance to do a good job of determining the edges of debris covered glaciers or discriminating the transient snowline from firn) or if you're wanting to assess glacier flow speeds, you need to resolve many details on the surfaces of the glaciers; you can do that over the debris-covered areas, but not, usually, on low-debris areas, where the glaciers are most commonly saturated.  If you want a DEM of the glacier for hypsometric work, you're mostly out of luck or have just one good quality snapshot over the lifetime of ASTER; it's not a case of missing 1 or 2 or 3 years, but one of missing 7 or 8 years (sometimes all 9 years) of GLIMS gains and working with 1 or 2 or 3 or 4 years of non-GLIMS gains and cloud or haze-plagued areas of those.  To some extent, it's just that Alaska tends to have miserable weather, and by 10:30 or 11 AM when imaging happens on rare mostly clear days, either morning clouds or late morning thunderstorms are already building; basically, as a desert-dwelling desert rat, I can say that Alaskan weather is pretty miserable, and it shows in the imaging record.  
So the image record is wonderful to have, offering great analysis potential for certain types of things, but it's not the GLIMS record that we originally set out to obtain.  We are down a factor of five to eight  relative to that (in Alaska), and a factor of two relative to what I think is minimally needed to achieve almost all of GLIMS's goals.  And it is NOT that ASTER is somehow the wrong tool; it's a great tool, even without SWIR, and the GLIMS plan is a great plan that in theory should work. 
Many parts of the non-polar glacier world are much better imaged than Alaska, and many areas are less well imaged.  There are almost no parts of Greenland that are in such condition, though Slawek and Gordon are right, that changes occurring there are so dramatic and rapid, and so consequential for sea level and future dynamic responses to climate change, that we cannot afford to lose the contributions of a valuable Earth observing asset for 2 years running.
One thing that I hope happens this summer, starting in just days, is acquisition of a fairly good 2009 record.  But a supplement to G:LIMS would be good to have in the types of priority areas I mentioned earlier today (gap filling, and high-priority targets).
--Jeff
   

> From: timberwolf at alaskapacific.edu
> To: fpaul at geo.uzh.ch; jeffreyskargel at hotmail.com
> CC: gordon.hamilton at maine.edu; tulaczyk at pmc.ucsc.edu; william.sneedjr at maine.edu; stearns at ku.edu; glims at flagmail.wr.usgs.gov
> Date: Mon, 25 May 2009 19:16:09 -0800
> Subject: RE: GLIMS Update: GLIMS ASTER image coverage and research documentation
> 
> Frank, Jeff, and all-
> I have reviewed most ASTER scenes pre-2008 of the most-glaciated portions of Alaska south of the Brooks Range and North of the Southeast Alaska area.  I found between 150 -200 scenes useable at least in part for perimeter mapping (I was looking for ice dammed lakes), and maybe 50% of these were from late in the melt season.
> 
> The holes in imagery are greatest over the southern third of the Alaska Range down toward the first volcanoes of the Aluetian Range, and in the St. Elias/ Coastal Range surrounding the junctions of Yukon/BC Canada with Alaska. These were the only areas lacking sufficient ASTER imagery to complete a detailed manual review of glacier perimeters.
> The area of greatest need for ASTER cover is about 60-62 deg North x 152 - 154 deg West.
> Thanks
> Dave Wolfe
> Glacier Dammed Lakes of Alaska
> timberwolf at alaskapacific.edu
> ________________________________________
> From: owner-glims at flagmail.wr.usgs.gov [owner-glims at flagmail.wr.usgs.gov] On Behalf Of Frank Paul [fpaul at geo.uzh.ch]
> Sent: Monday, May 25, 2009 3:45 AM
> To: Jeffrey Kargel
> Cc: Gordon Hamilton; Slawek Tulaczyk; william.sneedjr at maine.edu; stearns at ku.edu; GLIMS mailing list
> Subject: Re: GLIMS Update: GLIMS ASTER image coverage and research documentation
> 
> Dear Jeff and all
> 
> Thank you for the extended comments on GLIMS acquisitions by ASTER. I am
> sympathetic to most of your points and would like to add a few general
> remarks that might help to constrain the issue. From my point of view the
> use of ASTER data in GLIMS can be roughly classified in three groups:
> 
> (1) Glacier outline mapping for the purpose of a global glacier inventory
> (`snapshot' over a ca. 5 year period) -> must be largely cloud free & from
> the end of the ablation period/dry season
> (2) Scientific research projects (albedo, snow cover, lakes, debris, ...)
> focusing on specific regions / individual glaciers -> could be partly
> cloudy but should be taken at a specific time
> (3) Repeat imagery from rapidly changing targets (e.g. glacier
> lakes/hazard situations, Greenland outlet glaciers). -> needs frequent
> update of many but small regions
> 
> I further identify three huge changes in the past 5 years that were not
> clear during the set-up of GLIMS and ASTER STARs:
> (A) freely available and already orthorectified Landsat scenes from the
> USGS archive: This makes the use of ASTER data for purpose (1) nearly
> obsolete
> (B) rapid changes of Greenland's outlet glaciers: these regions should be
> clearly specified and regionally limited for ASTER data acquisitions
> (C) massive downwasting of glaciers in many parts of the world that could
> be quantified from repeat DEMs: ASTER DEMs will provide an increasingly
> valuable resource for this purpose
> 
> Two additional points have to be kept in mind regarding the sensor
> capabilities:
> ASTER has a 60 km swath with 15 m resolution while Landsat offers 180 km
> with 30 m pixels (or 15 m for ETM+ pan). In this regard I would say that
> ASTER is not the appropriate sensor for monitoring the two ice sheets and
> their outlet glaciers or ice streams. Moreover, Landsat7 data are
> available (orthorectified!) a few days after acquisition which is in my
> opinion an extremely valuable resource for the monitoring of Greenlands
> outlet glaciers (despite the scan line corrector stripes).
> 
> On the other hand, the proposed annual interval for glacier mapping or
> even one good image in 5 years was maybe over-optimistic. While such a
> frequency might work well in dry regions under constant high-pressure
> systems like in Greenland, it does not work out for maritime (Alaska,
> Norway, Patagonia, New Zealand), tropical or monsoon type climates. Even
> in the Alps the frequency is not higher than every 5 years (with Landsat
> coverage!). As far as I know, after 10 years of acquisition we have now
> two strips from ASTER (23 Aug 03 & 8 Sep 04) that could be used for
> purpose (1) and maybe a dozen strips for purpose (2). Please also keep in
> mind that it took 22 years (Sep 2006) before a useful image for purpose
> (1) of Jostedalsbreen (Norway) was acquired by Landsat 5 ...
> 
> To conclude, I am in favour of Jeff's suggestion to prepare an update of
> ASTER data that has been used for GLIMS so far by all RCs (indicating
> whether the purpose was 1, 2 or 3 from above) and provide information on
> the regions that are still lacking appropriate coverage. For Greenlands
> outlet glaciers (purpose C) I propose to identify a set of key regions
> (shape file polygons) that are of utmost importance for frequent
> monitoring with ASTER that are hardly covered (e.g. due to severe
> striping) by Landsat 7. Please keep in mind that Landsat 7 ETM+ could
> not be used since 2003 for purpose (1) and only partly for (2).
> Hope this helps and looking forward to your feedback!
> 
> With best regards, Frank
> 
> 
> PS: sorry for the long email :)
> PPS: The upcoming ASTER GDEM will be the most important breakthrough in
> creating a detailed glacier inventory (i.e. incl. topographic attributes)
> from all glaciers and icecaps north of the SRTM3 coverage.
> 
> 
> 
> 
> 
> 
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