Error occurring during the Terrain Flattening step

Microwave Toolbox
1

Hello,
I am trying to detect landslide-affected areas using Sentinel-1 GRD data. I am currently using SNAP 13.0.2.

Below is the preprocessing workflow I have followed:

  1. Thermal Noise Removal

  2. Remove Border Noise

  3. Slice Assembly

  4. Apply Orbit File

  5. Calibrate (in this step, I generated Beta0.)

  6. Terrain Flattening (in this step, I generated Gamma0. I used the Copernicus 30 m DEM.)

However, when I check the output from step 6 (Terrain Flattening), the pixel values shown in Pixel Info are NaN. Could you please advise how I can resolve this issue?

I also have a question out of curiosity: in step 5 (Calibrate), there is an option to output a Gamma0 band. Is that Gamma0 different from the Gamma0 produced by Terrain Flattening?

When I read other papers, I sometimes see that studies used Beta0 for landslide detection. However, isn’t it more effective to use Gamma0 in mountainous areas?

Thank you

2

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3

Performing the steps in this order has always been working well for me:
Apply-Orbit-File → Remove-GRD-Border-Noise → Calibration → ThermalNoiseRemoval → SliceAssembly → Terrain-Flattening.

Does that help in your case?

Calibrating to Gamma0 during calibration just changes the normalization area but does not apply terrain flattening.
See this figure of https://doi.org/10.1109/Tgrs.2011.2120616:

image
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For mountainous areas terrain flattening is definitely a good idea.

4

Thank you very much for your response.
Even when I skip the noise removal steps and process a single scene using Apply Orbit → Calibrate (generate Beta0) → Terrain Flattening, I still get the same NaN pixel values.

5

Strange. Can you post the name of the GRD product?

6

The GRD file name is S1B_IW_GRDH_1SDV_20190702T213151_20190702T213216_016960_01FE9A_85B8.zip.

Additionally, I ran the same workflow on another computer using the same SNAP version and it worked normally. In that case, should I consider this to be an issue with SNAP on my computer?

7

It seems there might be an issue with the computer I’m using. When I downgraded from SNAP 13 to SNAP 12 and ran the workflow, it worked normally.