A SIGNIFICANT WAVE HEIGHT DEPENDENT FUNCTION FOR TOPEX POSEIDON WIND-SPEED RETRIEVAL/

The ocean surface roughness affects the radar cross section measured b y altimeters. The wind speed is responsible for this roughness and mos t of present algorithms use the radar cross section (RCS) to infer it. A few authors (Monaldo and Dobson, 1989; Glazman and Greysukh, 1993) emphasized the influence of the sea maturity on satellite measurements . They found a marginal improvement in wind speed retrieval by includi ng significant wave height in their algorithm. In this paper several P reviously established algorithms relating altimeter radar cross sectio n to ocean surface wind speed are first analyzed. The shapes of the RC S versus wind speed curves are shown to depend mainly on the minimizat ion methods used to generate the model functions. An empirical wind sp eed algorithm is then derived from the two altimeters (ALT and SSALT) on board TOPEX/POSEIDON (T/P) satellite using a quality controlled dat a set in which North Atlantic operational surface wind and wave analys es are collocated with altimeter ALT measurements. Unlike usual algori thms, this new function depends on both the radar cross section and th e significant wave height. The improvement in the TIP wind speed estim ate seems significant at the 99.9% level. The accuracy of the derived function is evaluated using an independent collocated SSALT and numeri cal weather prediction models data set. Here again the improvement is significant, but at the 90% level because of the smaller amount of dat a available. The T/P wind speed estimates are furthermore compared to collocated estimates from National Oceanic and Atmospheric Administrat ion data buoys: the new algorithm retrieves wind speed from Geosat mea surements with an accuracy compatible with usual algorithms.