Dark strips in Sentinel-1 scenes


I encountered some abnormal dark strips in Sentinel-1 GRD products taken over the Eastern Mediterranean Sea on 6 October 2023 with the absolute orbit number 050639 and data-take identifier 0619CA. The screenshots below show the preprocessed scenes, but you can also find them in the GRD products. Does anyone have any clue why these dark strips appeared?



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It could be a too aggressive RFI mitigation, but this is just a guess, I would need to look at the data carefully.

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Dear @avalentino,

In fact for S1A_IW_GRDH_1SDV_20231006T035247_20231006T035312_050639_0619CA_430D the SAR processor does not detect any RFI here and hence is not mitigate anything.

The issue is that there is a large number of downlink missing elements (818 in total of each polarisation) as mentionned in the annotations.

Large number of missing elements is classically producing dark k strips.
I suspect as well that depending on part of the data missing, this may have a side effect either on azimuth compression leading to the bright patch on bottom right (to be confirmed) or and FDBAQ error (to be confirmed).

Same comment for the other image.

Dear @ghajduch,

Thanks for you explanation, it sounds reasonable. Now I also found information in the annotation files:

However, regarding the bright patch showing on the bottom right, I was wondering if it is due to Radio Frequency Interference (RFI) as it appeared in other scenes covering this area (but different locations), for example the products 12 days earlier on 24 September 2023 with the absolute orbit number 050464 and data-take identifier 0613CC:

I compared them with other threads:

The first two show smaller coverage of the artifacts, which seems to be closer to what I encountered in this area (near Egypt). However, I am still not sure if that would be the reason or it was due to error on azimuth compression that you mentioned.

This looks indeed like an RFI, and the fact that such pattern is observed on previous images on the same area (and without missing lines) is a good indication that this is an RFI that is not detected by the processor and not mitigated.

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