ALOS PALSAR deskew black hole

When I do the deskew processing on ALOS PALSAR L1.1 images, the deskewed images are discontinuous, and with black holes. SRTM HGT DEM are selected. Did anyone tell me why this happened? I will be very grateful.

Have you tried another DEM, for example Copernicus 30m?

Yea, I tried all the DEM options, but the results didn’t seem to change.image

Did you install the latest updates of SNAP (Help > Check For Updates)? Copernicus 30m should be among the list.

Also, what preprocessing was applied? Looks like the lines were introduced earlier already and the radiometric resolution is somehow limited.

Thanks for your reply. I will update and try Copernicus 30m DEM. The SLC image was downloaded from ASF. There was no other processing before the deskewing. I checked the image before deskewing and there were no “black holes”. There is no problem with some images after deskewing processing. I don’t know what caused the problem.

can you please share the image ID?

The image ID is ALPSRP020683220.

I get the same results when I follow your processing (directly apply deskewing on the raw data). According to the ALOS tutorial you can apply multi-looking before deskewing to solve it.

WOW, that is good. Because I will do the range spectrum split processing after the deskewing, I’m afraid the multi-looking processing will damage the spectral characteristics of the image. (I am not sure, but I will try).

I see. Then you can process the image as far as you can and lastly apply multi-looking and deskewing.

Thank you very much for your advice. I coincide with you on this point.

If you are going to do range split-spectrum analysis, you must do it before deskewing or any other resampling.

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