Abnormal deformation/(phase unwrap) by SNAPHU

hi everyone
here, i used SNAP to obtain a deformation map( Sentinel:20150706-20180714), and the step “phase unwrap” was handled by snaphu.

however, here i have encountered several problems:
(1) i don’t know where the step i should choose "reference ponit’ in “pahse unwrap”, so that the deformation map has no reference point.
(2) and the deformaion map has some abnormal information, for example,here , the blue polygon represents a lake, but it actually has some strange deformation informations.
(3) finally, the deformation information here seems to have a northwest-southeast distribution trend. i don’t what reason cause it…
please ,can anybody help me?
Thank you sincerely

I’m afraid the time between both images 2015-2018 is way too long for reliable results. The phase information is probably completely decorrelated and therefore produces random patterns.

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Can you please share with us a bit more of information for trying to understand what is happening?

  1. Which is the DInSAR wrapped interferogram are you trying to unwrapped? Do you have its associated coherence map?
  2. Which is the configuration you have used for unwrapping? DEFO/TOPO ?

Let us know.

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There has been a lake outburst here, which may lead to sedimentation around the lake.
So, I want to use InSAR to get the deformation around the lake.
and this is the coherence map:
For unwrapping,i use the DEFO/TOPO configuration.
Maybe, as @ABraun said, the baseline is too long to obtain the wrong deformation.
I am planning to do it with a shorter time baseline.
thanks very much.
finally, I still want to know about the reference point in “phase unwrap”/“deformation map”
I hope you can give me an answer.


Well, you cannot use the DEFO/TOPO, you should define only one.

As the unwrapped phase looks like a linear trend, I would suppose you have used TOPO (even if you probably applied the TopoPhaseRemoval on the interferogram computation because you wanted to compute the deformation (so you should apply TopoPhaseRemoval)

Please check and if I am right, change TOPO by DEFO and repeat the unwrapping with snaphu again.

Let us know.

PS: still, it looks a bit to me that you better apply another type of deformation technique such as SBAS or PSI instead of only DInSAR, as this technique is applicable for earthquakes and eruptions, but not deformation rates of mm/yr (or few cm/yr)

Dear Jose,

I’d like to ask you here about SBAS, since SNAP doesn’t support preparing data for SBAS, but in the same time the other part of SBAS, is supported by Stamps, what is the solution at the moment ?
Our colleague @thho gave good solution, but if you have other shortest way, especially to me at the moment, because I’m using VM.

In fact, the solution given by @thho is the only one I have known.

Not clear the relationship between a VM and the shorter way you asked for, but still I do not have/know anyother way to do it at this moment.

Good processing!

thank you very much @falahfakhri @mdelgado
Maybe,i will try the SBAS method through isce software.:grinning: