High resolution wind fields from satellite borne SAR

Abstract

An algorithm is introduced, which is designed to retrieve high-resolution wind fields from C-band synthetic aperture radars (SAR) operating at both vertical and horizontal polarization. The wind directions are extracted from wind-induced streaks, which are approximately in line with the mean wind direction near to the ocean surface. The wind speeds are derived from the normalized radar cross section (NRCS) and image geometry of the calibrated SAR images, together with the local wind direction retrieved from the image. Therefore the semi empirical C-band model CMOD4, which describes the dependency of the NRCS on wind and image geometry, is used. The CMOD4 was originally developed for the scatterometer of the European remote sensing satellites ERS-1 and 2 operating at C-band with vertical polarization. Consequently CMOD4 requires modification for horizontal polarization, which is performed by considering the polarization ratio. To verify the algorithm, wind fields were computed from the European satellites ERS-1/2 and ENVISAT SAR as well as the Canadian satellite RADARSAT-1 and compared to results from numerical models and a scatterometer.