Making interferogram for TANDEM-X bistatic mode

[ABraun]

I haven’t tried it myself but according to the documentation, you downloaded the correct data and put them into the right folder.

A similar issue was reported (and somehow solved) here: Iceland Aster DEM Coregistration Auxdata

How about my solution on manually creating a mosaic from the DEM tiles and use this as an external DEM?

[marjanmarbouti]

OK. I read what he did here but anyway he did not explain

Iceland Aster DEM Coregistration Auxdata

I’m glad you solved it. Maybe you can explain a bit more how you found out that all required tiles were not included and a bit about the hidden folder in OSX. Just in case there are people who have the same issue some day.

How can creat a manually mosaic from DEM?

[marjanmarbouti]

One more thing about ACE30 DEM,

I did not work with DEM result before, but in my idea, when I subtract the downloaded DEM (ACE30 DEM) _figure1_from the result (my created elevation) _figure2_and create a difference image in the band maths. If the DEM has high quality, the difference should be very little.

Am I right? If so, based on difference result between DEM and my elevation result, the difference is between (-3.32 to 18.35)figure3.

I think it is too much! Is’not it?

figure1.

figure2.

figure3
Or maybe, I should do some calibration first on my elevation result (for instance, subtract height value at a stable point like airport here and add 13 m (resulting in sea level reference))) and then compare my elevation result with ‘ACE30 DEM’?

[ABraun]

How can creat a manually mosaic from DEM?

load all ASTER files into SNAP and combine them into one large raster with the moasic tool.

Comparing your InSAR elevations to the ones from the DEMs is not a good idea because they wer created based on different data and methods. Additionally, if they have different spatial resolutions, they are not suitable for subtraction from your InSAR elevations.

But you need a DEM for proper terrain correction of your InSAR elevations and I would suggest to use ASTER.

[marjanmarbouti]

There are some ways to do mosaicing in SNAP but as our data are not SAR products, I think we can only use mosaicing in SNAP.
I used below steps;
Raster…Geometric operation…mosaicing

Then I added all zip files and I chose UTM zone_parameter projection=4_ here (figure 1) and when I went to another step (variable and condition), then I got this error(figure2).

figure1

figure2

Is my way right? Shall I use something for variable and conditions? How about ‘map projection definition’?

[ABraun]

Firstly, you will have to stick to “Geographic Lat/Lon WGS84” as an reference system, don’t use UTM CRS (explanation is here: Georefrence in snap)

The other thing is, you have to select a variable. In your case, it is just “band 1” as each Tif has only one band:

All of this is described in the help section, do you even look at it?

[marjanmarbouti]

Yes I read it but my problem is that when I press on variable folder (the picture in figure1) then it does not open a band chooser.

Figure1

[ABraun]

have you entered all tiles in I/O Parameters?

[marjanmarbouti]

Yes but my format is zip in ‘source product’.

[ABraun]

then try extracting them and add the rasters instead.

[marjanmarbouti]

Ok…l managed to make it by your help but lets explain my step to be sure, everything is OK;

In ‘map projection definition’, I left stuff like below (figure1);

Then my result is saved in ‘BEAM-DMAP’ format (figure2):

fihure2.
then I converted unwrapping file to elevation(figure3);

Figure 3.

And the result is here (figure4);

Figure4.
Is it OK?

[ABraun]

very good!
I want to be mentioned in the publication then

[marjanmarbouti]

Exactly, you helped me a alot. It is my pleasure:slightly_smiling_face:.

[marjanmarbouti]

Some more notes:

1. How can compare my elevation result with ‘ASTER DEM’. There is a option to adding band for ‘ASTER DEM’ but it is empty. Shall I subtracted the mosaic I made from my elevation result for checking quality?
2. You told me:

As a last step, you can apply Tange Dopper Terrain Correction so both elevations are projected into a coordinate reference system Then you can stack them and compare the elevations.

Shall I do it now?
I tried to do it (figure 1) but them my result is like this (figure2). I think something is missing in image.

figure1.

Figure2.

[marjanmarbouti]

Another thing that is weird for me is here;
Why when i applied terrain correction by using external file, the result is bigger that my elevation result. Please look at below;

[ABraun]

1. Only use the elevation generated by InSAR as the input (as you did)

2. Using the ASTER here is totally fine. Make sure you check “DEM” in the terrain correction step. This writes the ASTER DEM in UTM coordinates into your target product so you can compare later.

3. Uncheck “Mask out areas without elevation”

4. If you do this with the InSAR elevations of both dates, the results will be of the same size and coordinate system and then you can select “Radar > Coregistration > Stack Tools > Stack” to bring them into one final product.

[marjanmarbouti]

This writes the ASTER DEM in UTM coordinates into your target product so you can compare later.

I made elevation result and the ASTER DEM in UTM coordinates (figure1) but it seems a little strange although I did not work with DEMs but why the ASTER DEM has DEM over some area of ice and does not have DEM over other parts?

[ABraun]

Have you checked how the ASTER dem looks in the mosaic?

Are you sure what we see is not the ACE30?

ASTER has 30 meters spatial resolution which is resampled to the resolution of the TDX data.

[marjanmarbouti]

This is something that I got from mosaic.

[marjanmarbouti]

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