ocean wind retrieval from S-1

[RalphFoster]

I am trying to use the SNAP 7.0 wind field calculation under Radar -> SAR applications -> Ocean Applications on the VV band from an IW image (GRDH) image in the Baltic Sea. I have calibrated to sigma0. I also ran the de-speckler tool. The windspeed function appears to run, but returns all wind speeds as 0.1, which I assume is a default low value. The overlay is just red asterisks (I assume for indeterminate wind ambiguities).

I experimented with wind vector cell size, but no affect on the results.

Have I missed a step?
Where is the documentation for the wind retrieval function?
Is there a description of the algorithm?

Visually it’s fairly apparent that that there is a cold air outbreak evolvng into a more convective PBL. So, there should be wind speeds from at least 5 to 7 m/s down to just a few m/s.

[ABraun]

Is there a description of the algorithm?

It is based on this work: https://www.ecmwf.int/sites/default/files/elibrary/2003/9861-cmod5-improved-geophysical-model-function-ers-c-band-scatterometry.pdf

I’m not sure about your issue but there are some discussions on this tool which might give you some hints:

• Wind Field estimator bad performance for strong winds (S1A data)
• Wind field estimate results different VV and VH
• Wind Field Retrieval Result Report - Same location but different wind speed estimates
• Wind field estimation for S1-SLC
• Wind speed from Sentinel-1 images
• Wind field estimation results are incorrect

[efiliten]

@RalphFoster
Try run the wind speed estimation tool without having calibrated the image because a calibration step is included in the tool itself (so you end up calibrating twice).