Cross interferometry ERS-ENVISAT

Microwave Toolbox Interferometry
#1

Dear forum,
I am trying to perform a crossINSAR workflow between ERS-2 and ENVISAT to exploit the large baseline between the two
images and the 30 minutes acquisition difference in order to create a DEM.

I performed correctly the orbits application, the cross INSAR resampling (I tried ERS to ASAR and viceversa), then the coregistration and everithing run fine.
But when I tried to compute the interferogram then the processing does not go on and I received any error message.
My version of SNAP is the 4.0.
Any idea why I got this error?

buendia

ERS coregistration
Cross insar ERS-ENVISAT range filter
#2

Hi buendia

I think you should first update your SNAP version. The current one 5.0.7.
Please download the SNAP 5 installer and perform a module update (Help / Check for Updates).
This might already fix your problem.

#3

Dear Marpet,
I updated the software to the new version but I still encountered the same issue.
regards

buendia

#4

I was able to reproduce the error. Interferogram generation doesn’t start for ERS/Envisat stacks. Same for coherence.

GPT results in Error: null

#5

hallo ABraun,
thanks a lot for the check. Is there any possibility to solve this issue in the new SNAP release?
regards
buendia

#6

Could you fully document the input datasets & processing steps needed to recreate the issue?

#7

hello mengdahl,
I used as input dataset for SNAP two images optimised for the campain november 2008 - april 2009 tandem ERS-ENVISAT acquired the same day with only 30 minutes discrepancy.
The two images in track 351descending are the following
SAR_IMS_1PNESA20090116_095621_00000017A143_00351_71848_0000.E2
ASA_IMS_1PNESA20090116_092559_000000182075_00351_35976_0000.N1

  1. I load the two images
  2. I applied the orbits file to both images
  3. I chose the ERSas master therefore I resampled the ENVISAT with the Cross INSAR resampling method to ERS
  4. I coregistered the two images
    4a) in create stack I used the bilinear interpolation technique, initial offset method to orbit and the output extent to minimum.
    4b) in cross correlation step I used the standard parameters
    4c) in the warp I used the standard parameters
    Up to this step the software was running well.
    But when I tried to perform Interferogram formation the processor does not compute anything, it just stops.
    I also tried to resample in (3) ERS to ENVISAT but I ended up with the same problem.
    Thanks a lot for sharing a common interest on solving this issue.
    regards
    Buendia
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#8

Thank you all for pointing out the problem. It is a bug and has been fixed. The fix should be in SNAP v6.0 release.

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#9

Thank you junlu.
Do you know when it´s going to be released the SNAP v6.0?
regards
buendia

#10

It should be soon. At mean time, you can check the band names of your master and slave products to see if one product has polarisation in the band name (e.g. VV or HH) while the other does not. If that is the case, then you can simply rename the band by removing the polarisation (e.g i_VV to i). Then you should be able to do the interferogram or coherence.

#11

hello buendia
I am curently working on some research that needs ERS-ENVISAT cross interferometry data. I am wondering where I can find those data and really appreciate if you could kindly give me some instructions.

#12

You can download them from ESA via fast registration (account needed, will be granted within 2 days) here: https://earth.esa.int/web/guest/pi-community/apply-for-data/fast-registration

#13

Thanks a lot!

#14

Hello @buendia

How your cross interferometry already succeeded?
I just want to share my experience.
I have succeeded in making an ERS-Envisat cross-interferometry.

  1. First I did Apply the orbit file for the Envisat image

  2. In this case I changed the ERS image to ENVISAT in cross InSAR resampling without applying the orbit file before and after it.

  3. And perform the Coregistration, Interferogram formation, and Topographic phase removal processes successfully

image
image.png1920Ă—1080 682 KB

#15

You should perform “Cross InSAR resampling” on one of the scenes to get to co-registration to work well. Also, you’ll need a pair with ~2km baseline in order to have coherence.

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#16

Thank @mengdahl for reminding me, I have forgotten to write “Cross InSAR resampling”.

#17

It looks like the InSAR-phase is just noise (no correlation). Is the baseline close to 2km that is the requirement for cross-InSAR between ERS & Envisat to work?

#18

In this case I use baseline less than 2 km, but maybe cause the area in tropical country very dense vegetation so noise too high.

#19

It needs to be close to 2km due to the difference in central frequencies. You should look for data acquired during the ERS-2 & Envisat Tandem campaigns.

#20

Just a comment: ESA offers to search for image pairs with such parameters, such as minimum/maximum perpendicular baseline: http://esar-ds.eo.esa.int/socat/SAR-ASA_IMS_1P/pair_search

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