Making interferogram for TANDEM-X bistatic mode

I also put it on google earth and seems ok about location.

does it really look like this in your study area?

This is the image I have (green one).

I am trying to make a KMZ file from my result to see, if it is matched or not but then it gives me this error.

This is that area and is matched with DEM.

The area is right but I do not know why ASTER is in course resolution.

I downloaded this one,

Is it right?

Another idea, I made a mosaic and I think the resolution was changed after making mosaic.
Yes. Now I got the point, making mosaic reduces resolution.
Any idea about it?

that’s possoble. You can use the measure tool to see how large the single pixels are.
I see that you have just updated your post. Strangely, the DEM was resampled for mosaicing.

No the problem is with mosaicing…look at this

I just tried it with SRTM and they area also resampled to a lower reslolution.

I found its solution. We should manually adjust it.

good that you found a solution.
Orthorectifying the DEM doesn’t make much sense to me. But as long as the result is not distorted, everything is fine.

Dear @ABraun

If you remember, I tried to make DEM for 18 and 29 May (for example HH). Result of 29th May was fine but I think something goes wrong with unwrapping 18th May (figure1, 2,3).

I think because we have water in our interferogram (figure1). I do not know how SNAP does unwrapping and from where it starts to do.

How can I find unwrapping code or method that SNAP uses it for unwrapping? Do you have any idea about it? How this error would be solved?

Figure1. Interferogram

Figure 2. Unwrapping

Figure 3. DEM

you can mask out low coherence areas in the image using a valid pixel expression as described here: Subsidence map in 3d view) but this unfortunately doesn’t affect the uwnrapping process.

I don’t know how these can be excluded from the unwrapping but the basic algorithms are explained here:
Chen and Zebker are the authors of snaphu, unfortunately, the page is currently offline: https://nova.stanford.edusar_group/snaphu/

Thanks but by this way, it only affects on coherence result, not interferogram. So, again unwrapping would be failed.

One more question,

Is it possible that I use ‘special subset from view’ over interferogram and subset my area of interest OR should I do this over intensity before making interferogram?

It does, you use low coherence values to make these areas no data in the interferogram.

To your second question: this is possible for must sensors besides Sentinel-1 because of the bursts. Subsetting the interferogram for TSX/TDX is no problem!

Dear @ABraun
If we have two TanDEM-X pair (one in ‘18May in monostatic mode’ and another one in ‘29May in bistatic mode’), then it is possible to detect changes between them by using upper method that we discussed?

There are two approaches:

  1. InSAR: Make one DEM per date using the TanDEM images and compare the absolute heights you derived.
  2. DInSAR: Coregister the HH band of one image per date (e.g. HH of master 18May and HH of master 28May), calculate their interferogram and perform topographic phase removal (using the ASTER mosaic) and calculate the difference with “phase to displacement”. This however only works for coherent processes. And I am not sure if the perpendicular baseline between the two dates is suitable.

Both approaches rely in correctly generated interferograms and high coherence in the areas that are of interest to you.

Yes. I did before with two bistatic pairs but I did not know it is also possible with one bistatic and one pursuitMonostatic. Thanks

Why don’t you just give it a try?

These studies used both modes: I haven’t checked if they just compare or if they use monostatic pursuit and bistatic combined .

You don’t seem very confident about your ideas? :slight_smile: