The Order of DEM Creating Steps

about the statistical validation: Currently, there is no implementet accuracy assessment, but you could randomly place pins in your raster and export the elevation values of the SRTM and the S1 DEM and then statistically compare them outside SNAP.
Or you calculate a difference image (SRTM-S1 DEM) to see where they are alike and where there are the largest mismatches.

The pixel size which can be achieved is shown in the Range Doppler Terrain Correction module. To me it was about 13 meters when I tried it with your data. I’m quite impressed by the results.

Hi ABraun

Which was the coherence value???

coherence was mostly > 0.5



I will use this band and see if I can get a similar result

Thank you for the information. May I ask which software and tool did you use to calculate the difference between created and SRTM DEMs?

Your application with the same data resulted better as far as I see. And my coherence values were a bit lower. Did you use any other filtering like Speckle Filter?

@janaya I saw that you applied Topgraphic Phase Removal step. To generate a DEM, topographic phase should not be removed.

Many thanks, that was the problem! I also used TOPO instead DEFO in the snaphu.conf file, take a look to the result, much better now.

you can display the DEM by right-clicking on your SAR band and > add elevation band. It will then be downloaded and stored as an additional band. Open it to check if it is complete and has no errors and then you can use it in SNAP band math.

I only used Golstein Phase filtering after the generation of the interferogram.

What expression did you use to the show the differences in band maths?

elevation - elevation_VV

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I used the same expression as well, the difference didn’t appear visually distinguishable like the one appears as red areas.

Lastly, I know I’ve been too much, what is the reason for the perpendicular baseline to be negative and why does it change after coregistration?

can you show a screenshot of your data product and the difference raster?

About the second point I am not sure.

It looks like this closely;

the color table would be helpful as well. What is the range of your results?

Looks the same for me. Difference is mostly between -75m and +75m

Hi musicnerd

I found this from TM-19 ESA about baseline, I quote:

Once a ground reference point has been identified, the variation of the travel
path difference Δr that results in passing from the reference resolution cell to
another can be given by a simple expression (an approximation that holds for
small baselines and resolution cells that are not too far apart) that depends on
a few geometric parameters shown in Figure 2-2.

The parameters are:

  1. The perpendicular baseline Bn
  2. The radar-target distance R
  3. The displacement between the resolution cells along the perpendicular to
    the slant range, qs

I am sorry for the late response.

The case for difference doesn’t look same for me.

What can be the cause for it? As far as I can see, the only difference is the polarization I used. May it be the only cause?

I guess so. The trend is clearly similar to mine.

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please how to export the histogramme of coherence from sentinel 1 toolbox ?
thank you.

the whole forum is full of examples and workflows on how to do it. Just do a bit of research and you’ll find out.
The first post in this topic lists all required steps

InSAR processing with Sentinel-1 data is demonstrated here: (2 tutorials)

The theory behind InSAR is explained here:

If your study depends on it you should be willing to learn it instead of waiting for solutions coming to your inbox. If you have questions on specific steps, feel free to ask in here! But don’t expect others to do your research.

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I have a question in my mind with the usage of external SRTM datas.

What is the reason for SRTM DEM to be used during Phase to Elevation? And, is it only used for geocoding during Terrain Correction?