Help with Unwrapped Interferogram (SNAP & SNAPHU)

Microwave Toolbox
1

Hi everyone,

I’m trying to create an interferogram of Lower Austria for my bachelor’s thesis and have been following the NASA tutorial to do so:

After some trial and error, I was able to generate a somewhat promising-looking deformation map. Unfortunately, I later realized it was based on the wrong date pair, so I started over using the correct dates.

I followed the same steps as before:

  • Used 4-1 multilooking
  • Set the Goldstein filtering parameter to 0.6 (based on a paper suggesting it helps reduce cross-like artifacts)

Then I exported the wrapped interferogram and ran it through SNAPHU with the following parameters:
NTILEROW 5
NTILECOL 5
ROWOVRLP 100
COLOVRLP 100
NPROC 6
TILECOSTTHRESH 500
These are the same settings I used the first time.

However, the result from SNAPHU this time looks very similar to the wrapped interferogram

just with the colors changed. So now I’m unsure:

Was there an error in the SNAPHU unwrapping, or did something go wrong earlier in the processing chain?

I’m still new to interferometry and could really use help from someone with more experience. I’m aware that the area might not show much deformation, as there was no major event at that time except for heavy rainfall, but I want to make sure I’m at least processing things correctly.
This is the wraped Interferogram:

raw_2023.PNG
raw_2023.PNG1051×681 194 KB

And this the same one unwraped:

Unwraped.PNG
Unwraped.PNG1218×744 218 KB

I’m also attaching my first interferogram (from the wrong date) in case that helps evaluate whether it was even correct in the first place.

Scheibs_clip_unw_0_Overlap_Unw_Phase_ifg_17Apr2024_11May2024_0_Overlap
Scheibs_clip_unw_0_Overlap_Unw_Phase_ifg_17Apr2024_11May2024_0_Overlap1225×903 487 KB

Im using the newest Version of SNAP (11.0) on a Windows PC and the SNAPHU is done on a linux server with 64 gb ram
Thanks in advance! If I need to provide screenshots or files for troubleshooting, just let me know.

Best regards, Oceanman

2

Hi Ocean man,

I am trying out inteferogram as well. I am sorry, I do not have an answer to your question. I am posting here to seek your help.
i am trying out interferogram on downtown Toronto using sentinel-1 data. The two images are from June and September.

This is Phase_ifg_IW3_VV_26Jun2025_30Sep2025:

image
image1920×914 1.84 MB

When i unwrapped and converted phase into displacement, this is how it looks.

image
image1920×934 142 KB

I drew the line in horizontally to generate a profile plot. It is a line with negative slope.

  1. Total Change in Displacement : -3.9 - (-0.3) = -3.6 meters
  2. Slope (m):-3.6/1250 = -0.00288 meters per pixel, where 1250 are the number of pixels

So looking at the profile plot, it leads me to believe that the terrain is tilted, but this amount of tilt is impossible, so it must be because of the errors in the satellite positions when the two images were taken.

I am using Snap 13.0.0 version. And I do not know how to adjust each pixel for this slop due to error in satellite position. The band math does not allow me to add an expression where I can reference each pixel value.

Is my analysis correct or is it completely off? any help is appreciated.