Interferogram over ice

Microwave Toolbox
1

Hello everyone.

I am fairly new to SNAP and interferogram creation, and have been rather confused by a problem. I have checked through a number of threads on this forum before writing this, but I cannot find any answers. I am trying to generate interferograms over the South Patagonian Icefield (Argentina/Chile) with the objective of determining floating portions of ice outlets. I am familiar with the method for interpreting such interferograms and have seen it done in Antarctica, Greenland and elsewhere. However I am getting stuck at the interferogram formation and processing stage. I cannot get the interferogram to form any fringes whatsoever over ice, it always comes out simply as ‘noise’ (see figure below, specked area is ice). I am able to generate decent interferograms over land alone with the same tiles.

image
image.jpg2062×1327 1.55 MB

Is anyone here familiar with making interferograms over ice, and able to help me understand what is missing?

For info I have tried with several tiles ( and in other glaciated areas) and cannot get ice to resolve in any case.

Tiles used:
S1B_IW_SLC__1SDV_20190526T094342_20190526T094410_016413_01EE5F_6688
S1B_IW_SLC__1SDV_20190607T094342_20190607T094410_016588_01F39B_E4EC

Processing steps:
Coregistration with ESD > Interferogram formation > Debursting > Topographic phase removal > Multilooking > Goldstein Phase Filtering > Range Doppler Terrain Correction

As far as I can tell the problem arises within the first two steps. Could the issue be with ice losing coherence too rapidly for the 12 day image spacing to be usable? If this is the case does anyone have an idea which satellite data is generally used for glaciated areas?

Many Thanks-

Max

2

Snowfall destroys coherence very effectively. You could try with pairs from a dry period if there is one.

3

in this study of @marjanmarbouti , great interferograms were retrieved despite comparably low coherence, so maybe you are more lucky with another image pair.

A Study of Landfast Ice with Sentinel-1 Repeat-Pass Interferometry over the Baltic Sea

grafik
grafik.jpg925×510 225 KB

grafik
grafik.jpg929×718 268 KB

1 Like
4

Thanks for the rapid responses, that is very helpful. I will try and use Sentinel 2 imagery to identify a 12 day time period with no snowfall and report back about the result of it.

5

I have tried again with two snow-free dates (19 Jan-31 Jan 2019), however I was still not able to resolve the ice. It still only renders as a ‘speckled’ surface, without any coherent fringes.

image
image.jpg2003×1668 1.95 MB

Is there perhaps a processing step or setting that I am missing?

6

Hmm, perhaps the snow on the glacier was melting, which also destroys coherence. Dry still-freezing temperatures would be ideal.

7

That’s highly possible. I’m working for glaciology purposes and 12 days are at the very limit of applicability in my region. My “technique” (if I can call that) consists in computing every possible 12-days interferogram in my region and by chance, I sometimes had good results.

Fortunately, we managed to ask ESA to acquire our area of interest with a 6-days basis (S1-A + B). Note that S-1 is now at full capacity and don’t expect this solution to work again.

Cosmo-SkyMed have 1-day separated images. I see some glaciologists using this satellites with very good results.