Ramp in ALOS-2 ScanSAR swaths

[fdelgadodelapuente]

Good morning,

I Have a question about residual ramps in the ALOS-2 ScanSAR swaths. Here is an interferogram spanning the Southern Patagonian icefield. I processed 5 swaths, 3 frames and the following stitched intererogram shows a clear ionospheric phase as expected. However, the phase in swath 1 in frame 1 shows a clear ramp that is absent in the rest of the data.

The unflattened 150216-190128_1rlks_14alks.int interferogram for frame 1, swath 1 shows a band of decorrelation. The issue seems to arise when performing the image alignment and image multiplication before the swath and frame stitch. The orbital ramp in the rest of the unflattened interferograms look OK.

I'd appreciate some insights on how to correct this issue.

Thanks,
Francisco

[CunrenLiang]

Hi Francisco,

Using large matching windows would solve your problem. e.g.
< ampcor.setWindowSizeWidth(128)
< ampcor.setWindowSizeHeight(4096)

alosStack:
https://github.com/isce-framework/isce2/blob/main/contrib/stack/alosStack/estimate_slc_offset.py#L303-L304

alos2App:
https://github.com/isce-framework/isce2/blob/main/components/isceobj/Alos2Proc/runSlcOffset.py#L209-L210