Problems when using ASTER DEM with Sentinel-1

Dear Snap Developers,

I am trying to incorporate the Aster DEM into my S1 GRD workflows, where I:

  1. Apply Orbit File
  2. TNR
  3. Calibration to Gamma0
  4. Lin to DB
  5. RD Terrain Correction

It seems that no proper ortho-rectification takes place compared to the same workflow when using the SRTM 1 Sec DEM (see image, left processed with Aster, right with SRTM).

If I add the Terrain flattening, it puts out even no data when using ASTER (calibrating to beta0 before). While it is not a problem for areas covered by SRTM, it is for areas outside SRTM coverage.

I am using Snap 7 (latest relaease), on a Ubuntu 16.04 LTS with 8 CPUs and 32GB RAM.
Can you please investigate that?

Thanks,
Andreas

Andreas, the ASTER dem does not auto download due to licensing. Have you downloaded the tiles and placed them in the auxdata dem folder. Where did you get the tiles from? What do the file naming and file structure look like? It’s possible you have a newer DEM distribution where the file naming has changed?

Dear Luis,

I did not know that ASTER does not auto download. In fact, my aim is to automate as much as possible.
What would be a good alternative for arctic regions having automisation in mind?

Best,
Andreas

maybe the ArcticDEM is interesting for you: https://www.pgc.umn.edu/data/arcticdem/

Some solutions on downloading larger amounts of ASTER are discussed here: https://gis.stackexchange.com/questions/17989/how-to-download-the-entire-aster-gdemv2-dataset
But they would probably still have to be renamed according to the structure SNAP needs.

@lveci
New Version 3 seems now public domain.
Does this change anything?
https://ssl.jspacesystems.or.jp/ersdac/GDEM/E/3.html

@ABraun What is the structure that Snap needs? Is there any documentation on this?

Thanks in advance,
Andreas

according to this thread, you they need to be stored like this

.snap\auxdata\dem\ASTER 1sec GDEM folder\ASTGTM2_N00E111.zip

but this applies to version 2 and I have never tested it. But the path is the correct one (it is already created in the auxdata folder, but empty).