DEM generation

[ABraun]

you should select the HDR file in step 2 of the import, please check here: Problem in Snaphu Import section

But if your data already is .snaphu the import has worked fine I guess

[geodem1]

We did all the steps to get to extract images with palsar down from the vertex site, but I do not achieve the last step to extract, we have a debug sequence of the simulation of sar …, thanks for your help
I do not want to make dinsar just extract the dem

[reyhanrere]

@abraun do you know how to get good coherence ? is there any special value for azimuth coherence and range coherence ? Because the result of my DEM does not match the reality and SRTM DEM (there is a minus)

[ABraun]

short temporal baselines and suitable perpendicular baselines. Have a look at this document http://www.esa.int/esapub/tm/tm19/TM-19_ptB.pdf
Section 1.3 Selecting images for InSAR DEM generation

[geetha.sri82]

Hi pankaj

I too having same problem.

No .hdr file generated after snaphu unwrapping.

I saw your screenshots. You too have only unwrapped.snaphu.img file and no .hdr file

I also want to generate dem.

Did u get solution to this problem?

Can you share your results with me at geetha.sri82@gmail.com

Thank you

[rsneha]

Thanks i really liken it.

[ryeramirez]

Hi, @lveci!

I’ve came across this post in one of the forums:

“choose a pixel as reference point from terrain corrected product (with high coherence in time prefered) and check pixel value.
Next step: create a new band go to band maths (deformation band - reference point pixel value). This is the final deformation map.
Next you can create a coherence mask. Stack the final terrain corrected deformation map and terrain corrected coherence band. Create a new band to mask the coherence. Band math (e.x. If coherence band > 0.4 then 1 else NaN). You will have a new coherence mask band.
Final step: create one more new band. Band maths ( final terrain corrected defo band * coherence mask band).
This will be your final product.”

I already have a ‘Range-Doppler Terrain Correction’ band and I’ve done the first step which is creating a final deformation map by choosing a reference point. Please see screenshot shown below:

(Final deformation map - wrt a reference point)

I want to know exactly how to perform the following: coherence mask creation as mentioned above and the rest of the steps until I obtain the “final product” as mentioned, too.

I hope you can help me with this.

Thank you.

[saradhinird1]

Hi team
As we know SRTM DEM is the 30m resolution but for the better resolution drainage map, I tried to create drainage map from the Sentinel 1 data, While creating the drainage map from the Sentinel 1 data getting the wrong results.

I followed the entire discussion and I did DEM creation by following as you mentioned above steps;

1. S1 TOPS coregistration
2. Interferogram
3. Deburst
4. Topo Phase Removal
5. Goldien Phase Filtering
6. Snaphu export
7. Snaphu import
8. Phase to Elevation
9. Terrain corrections
   then the result is below fig,
   
   
   .

from the DEM out extracted data in CSV format and interpolated in QGIS then created Drainage map and is shown below

but the problem is while comparing the Sentinel 1 drainage output with the SRTM drainage output, the resultant is totally different, both are not matching even 5% also. what is wrong with this result could you please help me to get the better results.

Thank you in advance.

[falahfakhri]

I explained in the following post in some details, the selection and creation DEM from S-1 pairs

Source of the post

While in the following post, I explained the difference between the SRTM DEM as an example, and the once is formed by S-1,

Source of the post

[karoff]

I am new to SNAP and I am trying to create a DEM for the Ammassalik region in Greenland. I start with the following two steps:

1. Corregistration with “S-1 TOPS Corregistration”
2. “Interfarogram Generation”

The phases in the interfarogram show nothing but noise however.

I use GETASSE30 DEM for corregistration. Would it help do download the ASTER DEM?

I have tried to run different tutorials and that works fine for me. I have also tried a number of different image pairs to see if coherence was the problem, but each time the phases show nothing but noise.

Anybody, who can see what I am doing wrong?

[ABraun]

you can check if the coregistration was sucessful by creating an RGB of both intensities as described here: Fault marking by InSAR Data and difference between SLC_1SSV and SLC_1SDV?

Is there a reason why you selected exactly these two dates? For a more stable phase and higher coherence, you should aim for images with smaller temporal baseline. Also the perpendicular baseline plays a role. Have a look at this document http://www.esa.int/esapub/tm/tm19/TM-19_ptB.pdf
Section 1.3 Selecting images for InSAR DEM generation

[karoff]

Thanks for your rapid reply @ABraun, I have attached a RGB - does not look perfect to me.

As I could not get it to work, I tried a lot of different things, including changing the baseline and only using observation from Sentinel-1B, which resulted in a longer temporal baseline. In the RGB, I have changed that back, but it did not help.

Would it help to use the ASTER DEM for corregistration?

[ABraun]

Yes, the coregistration failed. Try to exclude the bursts over water in the Split step and also try other AutoDownloas DEMs.