My name is Rémi, this is my first post and first baby step into EO data processing with SNAP. After having spent some time admiring the “sea surface roughness” data from @ oceandatalab (see latest example of thread here twitter .com/remi_wnd/status/1125283025695248384), and following the advice from @ annamaria_84, I would like to ask a few questions.
Apologies in advance if some of the questions sound like i havent googled this enough, but I actually did try to do find some documentation, for ex:
*researchgate .net/publication/309185062_Rain_footprints_on_C-band_synthetic_aperture_radar_images_of_the_ocean_-_Revisited, suggested by @ Pierre_Markuse, or
- nersc.no/sites/www.nersc.no/files/01431160410001688286.pdf and
- mdpi .com/books/pdfdownload/book/529
Yet I could not figure out how to this with SNAP…
Let us say that I would like to compute the “sea surface roughness product” by myself, using for instance the image S1B_IW_GRDH_1SDV_20190504T054020_20190504T054045_016090_01E442_076B.SAFE (see the processed data here https://ovl.oceandatalab.com/?date=1556971200000×pan=1d&zoom=9&extent=549315.34883268%2C7207527.0638827%2C1332030.5183639%2C7598884.6486483&products=3857_SAR_roughness&opacity=100&stackLevel=100.01).
The info planel of oceandatalab reads “This product represents the small scales (5cm to a few m) Sea Surface Roughness, and is designed to be as independent as possible from viewing geometry. It is estimated as the ratio between the observed Sentinel-1 SAR backscatter and a model backscatter (CMOD-IFR2) for a constant wind of 10m/s at 45° from range direction.”
Could you point me to the existing papers or reports which explain the fundamentals of this sea surface roughness retrieval, and in particulat the part about “be as independent as possible from viewing geometry” and "small scales (5cm to a few m) ". I found many (see the third item in the list above), but where to start (efficiently) ?
How to compute this “model backscatter (CMOD-IFR2) for a constant wind of 10m/s at 45° from range direction” with SNAP ?
I am interested in these data, because they form the underlying dataset which is used for deriving 10m (neutral) wind speeds, for instance the data on https://satwinds.windenergy.dtu.dk/ (similar to the OCN product as I understand). The sea surface roughness data have a higher resolution, and although they may not be directly useable to compute wind speed (it require some kind of spatial averaging as I understand), many interesting flow features are more clearly visible on the sea surface roughness data than on the 10m wind product. See examples here:
- twitter .com/remi_wnd/status/1113166415790583811
- twitter .com/remi_wnd/status/1110909360643981312
Furthermore, I can often see features that look simlar in Sentinel2 and Sentinel1 data, which makes me wonder what these are. Sentinel2 data are somewhat “easier” to process than S1 data (i can use QGIS and matlab for instance), so having a better grip of the basics of SNAP for reproducing these nice sea surface roughness data would be nice.
Many thanks, and all the best from Denmark
Rémi (@ remi_wnd)