I am trying to coregister S-1A IW data over Greenland and I got the “java.lang.NullPointerException“
when using an external DEM (https://bpcrc.osu.edu/gdg/data/gimpdem) in the “Back-Geocoding”.
The graph I use is the standard “TOPSAR Coreg Interferogram.xml”. I tried the processing
step-by-step as well – same problem.
I am using SNAP 4.0.2 on Windows7, 32 GB Ram, i7. I tried to run the processing also with the
GPT – same problem. The processing succeeds when using ASTER GDEM and ACE DEMs
in the “Back-Geocoding” Tab.
The data I used:
The external DEM was saved as TIF in WGS84 using Geographic Coordinates Lat./Lon. The
DEM can be successfully used as external DEM in the “Range-Doppler Terrain
Correction”. It works as well when using the tool “DEM-Assissted-Corregistration”.
I tried to find the problem in “BackGeocodingOp.java”; however, I don’t see any problems
there (as far as I understand).
Thanks for help but my area is outside of SRTM (north of Sweden) and I plan to use an external DEM (one of my colleague sent me Sweden national DEM and I am using it) but I do not know why it did not work.
As I cannot use SRTM, so I used ACE30, it works but as you know it is not a proper DEM. I tried to use ACE30 for interferogram formation and subtract DEM by ACE30 but it said that
‘the resolution of the selected DEM is too low, please select a DEM with higher resolution’.