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CIA-Oceanix / MediSAR

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About the dataset #1

Open yellowfighter2333 opened 1 year ago

yellowfighter2333 commented 1 year ago

Hi! i‘m a beginner in SAR field. And I'm trying to achieve GMF in wind retrieval. How can I get information like wind direction data, incidence angle, and azimuth? Looking forward to your reply.

AurelienColin commented 1 year ago

Sorry for the delay, I didn't see the notification.

It might be tricky to recompute the GMF from this dataset, as the VV observation have been resized, quantized clipped, and has already been normalized by the GMF CMOD5.N to reduce the influence of the incidence angle.

The usual way would be to work from the Level-1 GRD product, which can be obtained either from the Alaska Satellite Facility or the Copernicus Open Access Hub. From the .SAFE, you can obtain the incidence angle and calibrate the SAR data to compute the sigma nought. I used proprietary code to process them and cannot share them, but the package xarray-sentinel seems able to do that as well. Then, you need to retrieve a prior on the wind direction (from ERA5 for example).

Once you have the wind direction (which need to be relative to the satellite heading), the sigma nought and the incidence angle, it is possible to use the GMF. On VV, there is an implementation of CMOD5.N in the openwind repository.