Measurements of the Effect of Rain-induced Sea Surface Roughness on the Satellite Scatterometer Radar Cross Section

Radar measurements of the sea surface, with satellite scatterometers that operate at Ku-band, will be affected by the presence of rain through modification of the sea surface roughness by rain impacts. This is in addition to wind driven roughness, atmospheric reflectivity and attenuation that affect the measured normalized radar cross section (NRCS). Numerous surface-based studies, using ocean platforms and wind-wave tanks, have shown the increase in the total NRCS can be significant and strongly dependent on radar frequency, incidence angle, polarization and wind speed [1], [2], [3]. Herein is the first study combining satellite based Ku-band data with high-resolution 3-D volumetric rain measurements, from simultaneous collocated NEXRAD data. The results to be presented were acquired during a significant rain event in the Gulf of Mexico just south of Houston, TX in May 2005. They are directly applicable to questions that are important to the interpretation of satellite derived wind vector estimates in the presence of rain of varying intensity and spatial distribution. This project is developing techniques to correct scatterometer derived wind-vector estimates. The acquisition of new knowledge on rain-splash effects is a necessary part of this effort.