Why my DEM made by S1A data have no elevation value?

After Deburst, the result is like this: all the district is purple and I can’t see any valueable information.

I suspect that there is a problem with the DEM used by Back Geocoding when coregister

After Coregister, there is nothing in Slave Intensity Image, is it normal?
Thank you very much.

if your data is simply purple, there must be an error before the interferogram generation step already.

yes, after coregister, the slave image have nothing. Could you tell me what’s wrong with the slave image, I tried to do this on another computer, but it doesn’t work.

I tried many times, every time after my S1 TOPS Coregistration, the Intensity_IW_slv image presents black.
No matter how I replace SAR data, the result is slave image black.

please name the products you use for image 1 and image 2 of the TOPS Coregistration

all these, when it use as master image is ok, but the slave image is always black.

I made a test with the first two scenes.
I used S1 TOPS Coregistration with ESD

  • Subswath IW3
  • VV Polarization
  • Bursts 1-3
  • SRTM 1Sec (AutoDownload) for the BackGeocoding

and left all other parameters as standard.

Worked out well.

I tried S1 TOPS Coregistration with ESD,but Intensity_IW3_VV_slv1 still empty, the RGB only presents Intensity_IW3_VV_mst1

I can’t reproduce this error, sorry.

I just solved the problem, I changed the Back-Geocoding DEM, I used my local DEM for Back-Geocoding. I think maybe my error is caused by the Great Firewall of China. Thank you very much!

The Unwrapping result is as fellow:

After Phase to Elevation:

It’s black again.

Phase to elevation also uses a DEM.
Change it to SRTM 3Sec or ACE30, for example

I finally made a DEM .

But the elevation ranges from 4000 to -4900 , that doesn’t match reality.

The extreme values don’t matter. They result from unwrapping errors and atmospheric disturbances of the phase signal. Have a look at your coherence layer. It tells you where the quality of the DEM is trustful.
If there is vegetation in your area, it is unlikely that you will receive a perfect DEM from repeat-pass InSAR because of temporal decorrelation.

1 Like

Could I do atmospheric correction before S1 TOPS Coregistration? How can I see the quality of the DEM whether it’s trustful or not? Could you give me more details? Thank you very much.

SNAP doesn’t support atmospheric correction.
Noise cannot be removed, only coarsely approximated subtracted from the phase. This is only possible with large stacks of images, for example by estimating the atmospheric phase screen (APS, short explanation here). This technique is not really suitable for common interferometry, but rather for persistent scatterer techniquest to derive surface deformations.

Values of high coherence tell you where your data is suitable. Please have a look at this post: Some explanations about concepts of fringes of interferogram and coherence

Besides that, ESA provides nice explanations on interferometry: http://www.esa.int/About_Us/ESA_Publications/InSAR_Principles_Guidelines_for_SAR_Interferometry_Processing_and_Interpretation_br_ESA_TM-19

Here you will find three documents:

Part A is for readers with a good knowledge of optical and microwave remote sensing, to acquaint them with interferometric SAR image processing and interpretation.
Part B provides a practical approach and the technical background for beginners with InSAR processing.
Part C contains a more mathematical approach, for a deeper understanding of the interferometric process. It includes themes such as super resolution and ERS/Envisat interferometry.

these two made the DEM201712
these two made the DEM201807
They both use the same reference DEM
Why the result value ranges gap so large?
What’s the DEM elevation unit? meter?

The unit is meter, yes. It is adjusted to the DEM used in the phase to elevation step.

There are many reasons why InSAR results are mostly not usable. The most important are temporal decorrelation, atmospheric effects and unwrapping errors. Here is a nice compilation of what can go wrong: https://eo-college.org/resources/insar_errors/

an example how atmospheric effects are reduced in time-series data of Sentinel-1 is given here:

source and full text: https://www.int-arch-photogramm-remote-sens-spatial-inf-sci.net/XLII-2-W7/597/2017/isprs-archives-XLII-2-W7-597-2017.pdf