RADARSAT ScanSAR Wind Retrieval and Rain Effects on ScanSAR Measurements Under Hurricane Conditions

RADARSAT-1 ScanSAR SWA images of Hurricane Katrina are used to retrieve surface wind vectors over the ocean. Collocated H*wind wind directions are used as the wind direction while the wind speed is derived from SAR sigmadeg by inversion of a C-band HH-polarization Geophysical Model Function (GMF) that is derived from the VV-polarization GMF, CMOD5, using a polarization ratio model. Because existing polarization models do not fit the ScanSAR SWA data well, a recalibration model is proposed to "recalibrate" the ScanSAR SWA images. Validated with collocated H*wind wind speed estimates, the mean difference between SAR-retrieved and H*wind speed is small and the root mean square (RMS) error is below 4 m/s. Rain effects on the ScanSAR measurements are analyzed for an incidence angle range of 22deg to 23.6deg using collocated ground-based Doppler weather radar (NEXRAD) rain measurements.