Buoy validation of ocean surface wind estimates from the TRMM precipitation radar

A technique has been developed for retrieving ocean surface winds using surface backscatter measurements from the Precipitation Radar (PR) of the Tropical Rainfall Measuring Mission (TRMM). Though limited by the small incidence angles and the single look capability of the scan geometry, TRMM PR offers a distinct advantage over conventional spaceborne scatterometer systems through the fine scale vertical and horizontal resolution of its normalized radar cross section, sigmadegrees. The wind retrieval algorithm developed for TRMM PR makes use of a maximum likelihood estimation technique to compensate for the low sigmadegrees sensitivity associated with the PR configuration. The narrow vertical resolution of the PR range bins serves to filter out rain contaminated cells normally integrated into scatterometer surface measurements. The algorithm was developed and validated through remotely measured winds from other spaceborne sensors, namely the TRMM Microwave Imager (TMI) radiometer and the NASA QuikSCAT scatterometet Further algorithm validation is presented using in-situ observations from oceanographic buoys. All buoy data are acquired from the NOAA National Buoy Data Center. The TRMM PR geophysical model function used in the retrieval process is verified through comparison of PR sigmadegrees measurements and buoy wind measurements. Ocean surface wind speeds derived from the new PR retrieval technique are then compared with collocated buoy winds, revealing excellent agreement in wind speed estimation.