TopoPhaseRemoval does not apply external DEM - defaults to SRTM 3

s1tbx Problem Reports
#1

I am using snappy to generate S1 interferograms.
I do back-geocoding and then ESD to generate a co-registered pair.
I then chain up the Interferogram > TOPSAR-Deburst>TopoPhaseRemoval modules.
I do NOT remove topohase during the interferogram generation step.
I pass the following external DEM parameters to TopoPhaseRemoval

parameters.put(“demName”, “External DEM”)
parameters.put(“externalDEMFile”, “TDX”)
parameters.put(“externalDEMNoDataValue”, “-32768”))
parameters.put(“externalDEMApplyEGM”, “false”))

The interferogram is then generated but in the processing metadata it reports that “demName” as “SRTM 3sec”.

I did not catch this problem at first and I have generated more than a thousand Interferograms. All of them have been flattened using the SRTM 3sec instead of the external DEM (not even SRTM 1 sec).

Is the “remove topography” during the interferogram generation step preferred over the TopoPhaseRemoval tool?

Can you please look into the apply external DEM with that tool? Particularly with Snappy - I suspect it happens with the GUI and GPT too but have not tested extensively.

This is a pretty bad bug if the user expected to use a high resolution DEM but instead ends up with SRTM 3sec

#2

for what it’s worth I don’t think this happens with GPT with snap 6.0.

I’ve run gpt TopoPhaseRemoval offline where there is no access to SRTM 3 and it runs fine. The metadata report the demName as external DEM

#3

We can delete this post - It seems like I have been making a mistake with my snappy parameter loading.

I essentially started my python script with

HashMap = snappy.jpy.get_type(“java.util.HashMap”)
parameters = HashMap()

And then every function would do:

parameters.clear()
parameters.put(“Arg”, “Val”)

I think I have not been clearing parameters properly all the time or loading parameters for two function without clearing in between resulting in some being remembered in the Hashmap causing strange behavior.

#4

thank you for reporting the solution. Shall I delete the whole topic or should I leave it so others can learn from it? :slight_smile: I leave it up to you.