I try to do coregistration with Sentinel-1 image use S-1 TOPS back-geocoding operator. After update to SNAP 7.0, I found that when the option “mask out area with no elevation” is selected, some area will be mask even if it is part of land rather than sea. Here is an example:
Master image intensity in coreg stack:
Slave image intensity in coreg stack:
The red polygon indicates the area which have been masked.
The external DEM show elevation in those area.
Also, this problem happen with SRTM3 DEM after testing.
Does anyone hit same problem? Is it a bug with new version of s1tbx?
Would you please to select SRTM 1SEC, this is an option, the other thing do your images have the same slice and orbit, might be the slave image doesn’t cover the burst or swath of master image.
If I understood correctly, both SRTM were tested and showed artefacts.
I don’t think it is related to orbit/slice because then the master image would not look correct either.
It looks like some sort of a tiling problem or propagation of null values. Have you tried selecting another DEM resampling method (e.g. NEAREST or CUBIC)?
Thanks for your suggestion. I will try. I though this issue is about dem null value, also. But as you see, the area with problem has data in dem in the last plot, which is output from DInSAR operator “output elevation band”. This problem doesn’t happen before, so I start to consider that may be a bug of SNAP.
By the way, SRTM 1c work fine just because different setting of no data value, so the result include ocean area where is 0 elevation in SRTM 1c DEM data.
OK, after some testing, this problem must be carried out with SNAP ver. 7.0 (s1tbx 7.0 / 7.2).
There are some result below:
Figure 1. S-1 images processed by SNAP 6.0 (s1tbx 6.0.6)
Figure 2. S-1 images processed by SNAP 7.0 (s1tbx 7.0.2)
All these result use same DEM, same nodata value, and same parameter in S-1 TOPS back-geocoding operator.
After a simple track in source code, I found some change may cause this problem:
Sorry I’m not a professional java developer, so I can’t test by myself. SNAP developers, please take a look, thanks.
I would like to know how to get the _asm.bin file in SNAP? Which operation can get the _asm file?
e.g., apply orbit file can get _orb file.
The _ASM file mean assemble two or more S-1 product in continue orbit, please use S-1 Assembly in Menu RADAR->S-1 TOPS to achieve that purpose.
Great thanks for your reply!