Problems to generate DEM

Hello all,

To present myself, I’m a new user of SNAP. I’m an intern in computer sciences and I had no previous knowledge of interferometry 1 month ago.

I want to generate a DEM but I’ve got many problems :

First, I use 2 SLC with the following processing chain :
Split -> Apply Orbit File -> Back Geocoding -> Interferogram -> Deburst -> Goldstein -> Subset -> Export Snaphu -> Unwrap the Phase -> Import Snaphu.

And when I try to use the tool : Phase to Elevation to generate my DEM, I have a NullPointerException with SRTM 3sec (Autodownload). Then I use SRTM 1sec(Autodownload) and it works, but I get an offset at sea level and thus on the rest…

  1. How can I set my 0 altitude to sea level ?

  2. Why do I get NullPointerException if I try SRTM 3sec ?

  3. Phase to Height always crashes while Phase to Elevation seems to work. Why does it crash and what is the difference between this two processes ?

Thanks for your help.