Operational scatterometry: high wind speed retrievals

Near real-time ocean surface wind vector retrievals from the SeaWinds scatterometer on QuikSCAT promise to greatly improve upon the ocean surface information currently available to operational marine forecasting. The impressive 1800 km-wide swath coverage and 25 km resolution of SeaWinds wind vector retrievals are a vast improvement over currently available ocean surface wind vector measurements. In an operational forecasting environment, an understanding of a measured quantity´s capabilities and limitations is just as important as its timeliness. The accuracy of high wind speed retrievals are important for determining the intensity of a storm as well as defining the gale force and storm force wind radii. The current Ku-band model function (NSCAT-2) appears to accurately predict the normalized radar cross-section (NRCS) up to around 30 m/s, which is about the upper wind speed limit contained in the matchup data sets used to empirically derive NSCAT-2, The C-band model function (CMOD4) departs from experimental data at around 19 m/s. Several field experiments recently conducted by NOAA and the University of Massachusetts have resulted in scatterometer measurements of the ocean surface in wind speeds up to 60 m/s. New model functions derived from these experiments are presented, and the impact of these new model functions on the scatterometer wind retrievals are evaluated for several cases