Application of state-of-the-art SAR X-band geophysical model functions (GMFs) for sea surface wind (SSW) speed retrieval to a data set of the Italian satellite mission COSMO-SkyMed

The concurrent presence of three satellite X-band SAR systems makes it interesting to test the interoperability of retrieval approaches meant for one system on the others. To approach this problem a description of the state of the art of the SAR X-band geophysical model functions (GMFs) for sea surface wind (SSW) speed retrieval is carried out. A sensitivity study of wind speed retrieval with respect to the wind direction when using the XMOD2 GMFs developed at the German Aerospace Center (DLR) and the Italian Space Agency (ASI) is presented. An application of these two GMFs to a series of data sets of stripmap images with vertical polarization VV acquired by the Italian satellite mission COSMO-SkyMed (CSK) is discussed, and the results of the SSW speed retrieval are compared to both the National Centers for Environmental Prediction (NCEP) blended sea winds and in situ buoy data from the National Data Buoy Center (NDBC). The retrieval exercises show that the two GMFs have similar performance. The sensitivity study shows that an error of ±10° may introduce an error greater that 10% in the retrieval of SSW speed.