GAMMA Questions

Hi all,
I'm processing glacier velocities using Sentinel-1 IW data. As a reference DEM for generating the geocoding lookup tables (gc_map), I’m using a merged SRTM-TDX Global DEM of Alaska at 8.333 10^-4 deg. spatial resolution. When using this DEM and a DEM-oversampling factor of 2, I expirienced no problems so far.

However, I recently wanted to decrease the resolution of the geocoded surface velocity fields for storage capacity reasons and to be closer to the actual resolution of the derived offsets. My first approach was to use a DEM-oversampling factor of 1 instead of 2. This left me with the error “insufficient valid offset points to determine offset polynomial, minimum number required: 3”, when calculating the geocoding lookup table. Hence, I tried to use a resampled version of the DEM (1.6666 10^-3 deg) and kept the DEM oversampling factor at 2. However, using the resampled DEM results in 0 accepted offset estimates during feature tracking. I tried several algorithms (gdal, ArcGIS) for resampling, but all of them give the same result. The problem is, that the script finishes without any error message. However, I found that already the coregistration is much worse than if using the DEM at the original spatial resolution. I assume that probably the resampling of the slave-SLC with SLC_interp_lt_S1_TOPS prior to the actual coregistration causes the problem, as it uses a geocoding lookup table that has been created with the help of the DEM. Nevertheless, I still could not find the final solution of the problem and I do not really understand the reasons behind. Does anyone of you have an idea, which could point me in the right direction?

Any help is very much appreciated. Thank you very much in advance!
Peter