After my interferometric processing, I see that my displacement map shows only zero and subsidence with any uplift estimations. For several tests I got the same results: no uplift. I unwrapped the interferograms by SNAPHU v1.4.2; the output correctly includes positive phases, however, where the unwrapped phase is expected to be negative it just resulted in zero. Could anyone help in this problem please?
How does the initial interferogram look like?
A raster completely filled with zero indicates an error in the previous steps.
Thank you. I do not get completely zero raster, actually my unwrapped maps always ranges from 0 to a positive value without negatives. If I inverse Master and Slave, the parts where showed positive in the previous map are now zero and the zeros are now positives. briefly, I do not see any negative values in my unwrapped maps for many tests (min: 0 max: x). see the image please.
It seems the initial interferograms are valid (see the phase and coherence maps associated to the previous image), that is why I think the problem occurs within the unwrapping step.
I’m afraid, this interferogram will not produce any usable results. It consists of pure noise, none of these patterns contains information about surface deformation. What you later produce in the unwrapping is a random pattern. Errors at early stages are propagated through the workflow: This is why the unwrapping results make no sense in the first place.
Please have a look at these tutorials, how displacements in inteferograms look like:
So you need image pairs with higher coherence, I think your temporal baseline (June 2006 to January 2007) is way too large.