Issue after using multi_cpx: resampled SLC shows dark top/bottom and bright center, causing poor co-registration
Added by wandi wang about 1 month ago
Hello everyone,
I would like to ask whether anyone has experienced issues with multi_cpx when resampling SLC data.
the resampled SLC looks abnormal when displayed in grayscale:the upper and lower parts become dark,the middle part becomes brighter.
Because of this, the image cannot be properly co-registered, and the interferogram quality becomes very poor.
I checked the data and found that this is not simply a display stretch issue,the amplitude distribution itself seems to be affected, as if multi_cpx introduced uneven amplitude values or edge padding.
Has anyone encountered similar problem with multi_cpx?
Any hints, explanations, or examples would be greatly appreciated.
Thank you in advance!
Replies (1)
Issue after using multi_cpx: resampled SLC shows dark top/bottom and bright center, causing poor co-registration - Added by Charles Werner about 1 month ago
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Hello,
The question is what are you trying to oversample or decimate and what the
specific problem you are trying to solve?
This program is meant to downsample (multi-look( for complex-valued
interferograms, in
the contex of phase unwrapping. For example using multi_cpx to multilook a
complex interferogram, unwrap the interferogram after multi-looking, then use
multi_real to expand the unwrapped interferogram, and then use that expanded
unwrapped interferogram as a model to unwrapp the original interferogram.
multi-looking the interferogram not only makes it smaller, but also has less
phase noise such that unwrapping
is managable (memory and time). Using the smaller unwrapped interferogram to
unwrap the larger non-multi-looked interferogram at higher resolution
is very fast (unw_model)
To over-sample SLC or RSLC data use the program SLC_ovr. Note, for Sentinel-1
data you can only oversample in the range-direction
due to the high azimuth phase ramp that prevents interpolation unless first
deramped.
Best regards,
Charles Wnere
On 04.12.2025 21:26, wandi wang wrote:
GAMMA Questions - GAMMA Processing: Issue after using multi_cpx: resampled
SLC shows dark top/bottom and bright center, causing poor co-registration
<https://dep1doc.gfz.de/boards/9/topics/680>/wandi wang/
Hello everyone,
I would like to ask whether anyone has experienced issues with multi_cpx when
resampling SLC data.
the resampled SLC looks abnormal when displayed in grayscale:the upper and
lower parts become dark,the middle part becomes brighter.
Because of this, the image cannot be properly co-registered, and the
interferogram quality becomes very poor.
I checked the data and found that this is not simply a display stretch
issue,the amplitude distribution itself seems to be affected, as if multi_cpx
introduced uneven amplitude values or edge padding.
Has anyone encountered similar problem with multi_cpx?
Any hints, explanations, or examples would be greatly appreciated.
Thank you in advance!
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