Snaphu/ers

MarineROGER · February 26, 2018, 11:14am

Good morning,

I created an interferogram based on ERS SLC data following these steps.
First could you tell me if it is correct (the final product seems fine).
Step 1: Apply-Orbit File (DELFT)
Create Stack
Cross correlation
Warp
Step2:
Interferogram
TopoPhaseRemoval
GoldsteinPhase Filtering
Terrain Correction
LandSeaMask

My problem appeared during the unwrapping
I have done the export snaphu
runned snaphu
But for the Import snaphu I am not sure which file I am supposed to use for the phase wrapped:
Phase.dim or Phase.hdr ?
For the unwrapped: the unwrapped.hdr ?

With .dim the result is not correct (see attached file)
and with both .hdr I can’t run snaphu import.

Could you give me some more information about this step ? For now I followed this tutorial: http://sentinel1.s3.amazonaws.com/docs/S1TBX%20Stripmap%20Interferometry%20with%20Sentinel-1%20Tutorial.pdf

Thank you
Marine

ABraun · February 26, 2018, 6:24pm

selecting the hdr file of the unwrapped phase should work. You need to select the product before unwrapping in the first tab. Please see here: Problem in Snaphu Import section

Edit: Your unwrapped interferogram doesn’t look that bad actually…

MarineROGER · February 26, 2018, 7:00pm

Thank you for your answer. Can I do something to improve the result ? I tried increasing the number of tile but nothing change.

Is it better to do the terrain correction before the unwrapping or is it better after as done in the tutorial ?

ABraun · February 26, 2018, 7:33pm

your results strongly relate on coherence and atmospheric conditions. If they are not good, there is no technical way to improve it.

Terrain Correction should be the very last step, after unwrapping and phase conversion.

MarineROGER · February 27, 2018, 4:44pm

Hi, I change my graph to stop the processing at the Goldstein filter, before the terrain correction. Done the unwrapping but now snaphu import is not working :
NodeId: 3-SnaphuImport; SnaphuImportOp requires input products to be of the same HEIGHT dimension.

What should I do ?

Thanks
Marine

MarineROGER · March 6, 2018, 11:10am

@ABraun

Hi
Do you know if for ERS it is possible to do the unwrapping before the geocoding ? See my previous message
Also the phase conversion is not doing anything, the window just flash for a second. I saw another subject about this but no solution.

Regards,
Marine

ABraun · March 6, 2018, 11:44am

I highly recommend geocoding after unwrapping.

MarineROGER · March 6, 2018, 11:50am

I understand that but when I plan to do the geocoding after the unwrapping I got this error in the snaphu import:
NodeId: 3-SnaphuImport; SnaphuImportOp requires input products to be of the same HEIGHT dimension.

Regards,
Marine

ABraun · March 6, 2018, 11:53am

If you select the product before unwrapping for 1 and the one after unwrapping in 2 it should definetively work.

MarineROGER · March 7, 2018, 10:47am

I don’t know what happen last time but it is working now !
Just the terrain correction is not correct. Do you know what is the problem ?

ABraun · March 7, 2018, 10:58am

looks like there is not enough coherence on the right side of your image.

MarineROGER · March 7, 2018, 1:16pm

Sure but look at this result:

left top is unwrapping and then Terrain correction
right top TC and unwrapping
bottom the interferogram wrapped

Regards,
Marine

ABraun · March 7, 2018, 1:42pm

Terrain Correction involves resampling of the pixels, that means new values are calculated. Maybe you should multi-look and filter your interferomgram before unwrapping.