High resolution wind fields retrieved from SAR in comparison to numerical models

Abstract

An algorithm is introduced, which is designed to retrieve high-resolution wind fields from C-band synthetic aperture radars (SARs) operating at vertical or horizontal polarization. Wind directions are extracted from wind-induced streaks, which are approximately in line with the mean wind direction near to the ocean surface. Wind speeds are derived from the normalized radar cross section (NRCS) and image geometry of the calibrated SAR data, together with the prior retrieved wind direction. Therefore the semi empirical C-band model CMOD4, which describes the dependency of the NRCS on wind and image geometry, is used. CMOD4 was originally developed for the scatterometer of the European remote sensing satellites ERS-1 and ERS-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 159 ERS SAR and 20 RADARSAT-1 ScanSAR images and compared to co-located results from the numerical models REMO and HIRLAM.