|Title||Ku-band radar altimeter surface wind speed algorithm|
|Publication Type||Technical memorandum|
|Secondary Title||ECMWF Technical Memorandum|
An algorithm for the retrieval of surface wind speed from Ku-band altimeter backscatter coefficient is proposed. The algorithm was derived using two-month (January-February 2005) worth of ENVISAT altimeter (RA-2) Ku-band backscatter data collocated with ECMWF model and buoy surface wind speeds. The algorithm was extensively verified using several collocated data sets including the altimeter Ku-band backscatter coefficient from ENVISAT, ERS-2 and Jason-1 and the wind speed from ECMWF model and from buoy observations over several years. The new algorithm increases altimeter wind speeds by about 0.40 m s-1 and reduces the scatter index by about 5% compared to the well-known "modified Chelton-Wentz" algorithm. The algorithm performs even better than the two-parameter algorithm implemented for Jason-1 altimeter. The proposed algorithm was implemented for ENVISAT RA-2 on 24 October 2005. Verifications over a year afterwards showed better performance in terms of wind speed retrieval. The use of significant wave height as a second parameter for the altimeter wind retrieval algorithms may not be a proper choice for high sea-state conditions. It seems that the backscatter coefficient saturates for each significant wave height which can not be exceeded irrespective of the wind speed.