The Improved C - Band Geophysical Model Function Cmod 5

This paper describes the performance of CMOD5, a new C-band geophysical model function, relating scatterometer backscatter to surface vector wind information over the global oceans. It was derived on the basis of a comparison of scatterometer triplets from the Active Microwave Instrument (AMI) aboard the ERS-2 satellite with collocated ECMWF first-guess winds. In addition, results from recent aircraft campaigns at hurricane wind conditions, were taken into account. CMOD5 resolves deficiencies, known to exist for CMOD4; the GMF on which the AMI wind product is based since 1993. It gives rise to a more uniform performance across the AMI swath. Improvements are especially obtained for extreme cases, for which it is shown that the dynamical range for C-band scatterometer data can be extended from 24 m s−1 to 35 m s−1 .