[Help]: SBAS results different from GMTSAR SBAS processing results

[kinreich]

Hello,
I ran a time series processing once using GMTSAR manual, and once using pygmtsar, and got very different results for

OS and software version

• OS: Ubuntu 20.04.5 LTS
• PyGMTSAR version: pygmtsar-v2023.3.11
• GMTSAR: 4.2.2

Steps to reproduce the problem
I ran the timeseries on 72 ascending scenes, and 107 interforgrams,
pairs : time was 30 days between them, as well as yearly pairs.
meters: up to 150 meters (default)
I used the same data in both of the processing analyses: same dem file, same wavelength filter, same corr file for correlation filter.

For GMTSAR they produce a velocity grid to look at, and for pygmtsar I produced a velocity grid from the total displacement divided by the time passed (in years).

I compared between the processing stages, and found that the differences in grd files are seen only after running SBAS (unwrap and phasefilt files see no difference)

Screenshot
Here is the velocity grd (mm/year) for pygmtsar analysis:

Here is the velocity grd (mm/grd) for GMTSAR analysis:

Could you help explain why we would see such a difference in final results with the two analyses?

[AlexeyPechnikov]

But what is the difference? You are only showing PyGMTSAR results without selecting a colormap or specifying a range. By the way, you are using a very old version of PyGMTSAR.

[kinreich]

I ran the analysis on pygmtsar a while ago, that's why its the older version.
I showed the results of both pygmtsar and GMTSAR, there are two png's of grids attatched.
You can see the great difference in the mm/year, although the trends are the same.

[kinreich]

Here I have attached another png that shows the difference in total displacement over 7 years:
Cropped Grid 1 is from GMTSAR aanalysis
Resampled Grid 2 is from pygmtsar Analysis
And you can see the difference grid as well (in mm)

[AlexeyPechnikov]

It seems you have not detrended your cloudy PyGMTSAR unwrapped interferograms before SBAS processing, but used GMTSAR atmospheric correction.

[kinreich]

I detrended PyGMTSAR unwrapped interferograms before SBAS processing, and didnt use atmospheric correction with GMTSAR

[AlexeyPechnikov]

Okay, show us your phase cleaned from stratified atmospheric phase delay and turbulence component, and show your displacement grids per date.