Interferogram from Alos palsar 1.1 data

Thank you very much @EJFielding for sharing the results with us. Indeed the results seem similar to what I have got, apart for the vertical stripes on my coherence results. Indeed ISCE shows very nice results, thanks again for helping us with this.

Myself while trying to go ahead with the TopoPhaseRemoval, I have identified and issue with SNAP. TopoPhase and elevation bands are shifted with respect to the InSAR results. See image below. Can you @lveci or @marpet open an issue for that? I think this is very important to solve it asap. Already some people approached me saying to had found something similar, specially in flat areas (also near Milan area happens). Thank you very much.


In the image: top row are the multilooked interferogram phase after TopoPhase Removal(left) and multilooked coherence (right). Bottom row are elevation (left) and topo phase (right). The shift are several kilometers (more than 20km in this case)!!!

Note: I have used SRTM DEM 1 Arc second

Steps:

  1. Read master and slave
  2. Create Stack :
    extent: Master
    resampling type: Bicubic interpolation
    initial offset method: orbit
  3. Cross-correlation
    fineRegistrationOversampling: 16
    only GCPsonLand: false
    gcpTolerance: 0.25
    fineRegistrationWindowWidth: 32
    fineRegistrationWindowAccAzimuth: 16
    fineRegistrationAccRange: 16
    rowInterpFactor : 4
    InSAROptimixed: true
    ApplyFineRegistration: true
    fineRegistrationWindowHeight: 64
    columnInterpFactor: 4
    maxIteration: 10
    coarseRegistrationWindowHeigth: 128
    numGCPtoGenerate: 10000
    coherenceThreshold: 0.6
    coherenceRegistrationWindowWidth: 128
  4. Warp:
    interpolationMethod: Cubic convolution (6 points)
    warpPolynomialOrder: 1
    rmsthreshold: 0.05
  5. Interferogram:
    substractFlatEarthPhase: true
    srpPolynomialDegree: 8
    srpNumberPoints: 1001
    orbitDegree: 5
    substractTopographicPhase : false (after seeing last post better not do it until solved)

I guess that some parameters had been exagerated, but I wanted to verify whether with SNAP we could solved the issues due mainly to, coregistration errors (causing low coherence at first instance) and secondly wrong FlatEarth estimated and removed, keeping finally the fringes due to ionospheric effects typical from L-band SAR systems.

After my last post, please verify always if topo phase is correctly removed. Seeing one of @Abraun posts it seem that the TerrainCorrection worked fine instead.

I hope this may help you.

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Thank you so much for helping me out, @mdelgado. Yes changing the parameters worked. But following the topographic phase removal, should I go for goldstein filtering, unwrapping, phase to displacement and then process it using doppler terrain correction at the end? If not, what should be the sequence now? Any of the parametric values need change?

Dear @draco, I am glad that you now manage to compute interferograms with the ALOS data. Just to mentioned that after applying TopoPhaseRemoval, please check the TopoPhase and/or elevation band (check for including them in the output) to visually verify that DEM is correctly aligned (in my example SRTMDEM 1Arc it was not the case). If TopoPhaseRemoval works just fine, the following steps are the ones you mentioned, but I would suggest to compute the plane that fits the ionospheric related phase contribution and remove it, otherwise your main contribution will not be only subsidence, but ionosphere related phase)

Another option would be to produce all the interferograms and try to proceed with PSI or SBAS techniques. Currently SNAP is compatible with StaMPS PSI but for that you need many interferograms to achieve good results (>20 interferograms are recommended).

Good luck! And let us know

Thank you so much @mdelgado. I read your message today :yum: I tried the SRTM 1 arc second in my case also. So when I opened the topo phase in the output it turned out beautifully! But once I do the displacement the resultant image is horrible!! Just similar random shades like before (post 56 below) !!

image
image.png1365x707 72 KB

I do not understand why the displacement looks so weird! I have no clue. :frowning:

And yes I wanted to process my images in this way. Could you please suggest a tutorial or a pdf where the steps are given?

Looking forward for your help. :slight_smile:

Please carefully reads this post: About the STaMPS category

you should compute the ramp related to the ionospheric contribution of the phase and remove it. The real deformation should be related to the remaining phase and not the one you show there.

Thank you for your response @ABraun. Are the steps applicable for Alos images?

I haven’t tested it, should be possible. But you need at least 25 images.

Thank you for the help @mdelgado :slight_smile: But could you please tell me how to do this?

Thank you for the suggestion @ABraun. I am short of 5 FBD images. Can I use FBD and FBS ones in that case?

You can combine FBD and FBS as long as both have one common polarization.

Oh great! Thank you so much @ABraun! :smile:

well, as you already have the unwrapped phase, you could open it using any mathematical software such Matlab or python and calculate the plane that minimises (best approximate) using least squares or so. Then once you got that plane, remove it from the unwrapped phase. Note that then you could have still other contributions in the phase and not only deformation, but you will be one step closer.

If you plan to use PSI or SBAS then this probably is not needed as that kind of processing normally correct those effects.

I hope this helps

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Well explained, @mdelgado
@draco: There was a discussion about ramps sone time ago. Please have a look at this post and the few following up: Subsidence map in 3d view

Thank you for the help @mdelgado. I will try this and inform you how it went. :slight_smile:

Thank you for your response, @ABraun. I will look into it and revert. :slight_smile:

Hello everybody!
Is there any progress regarding the issue with the shifted elevation and topo bands?
I have a similar problem of shifted bands, in the case of processing two ALOS SLC images (26/12/2006 – 31/12/2008, Bperp=255). SRTM 3arc was used in this case.

What drove my attention to check for this potential shift, in the first place, is the fact that before topography removal the interferogram was like that:

no_dinsar_default

And after topo-removal:

Something seemed to have gone wrong with the topography removal tool. I then read @mdelgado post…

So in cases like this what should we do? Just discard the pair?

Please note that for this particular case, the two acquisitions refer to different reception paths. Could this be the problem?

Thank you all in advance

Have you applied ALOS Deskewing before the topographic phase removal?
I wonder if it makes a difference if you do it before or afterwards.

Dear @ABraun,

thank you for your quick response.
No, deskewing was not applied since the images were provided by ESA (Alos-1 DInSAR Deformation Map). ALOS support team confirmed that the products do not need deskewing.