Corrections to Scatterometer Wind Vectors from the Effects of Rain, Using High Resolution NEXRAD Radar Collocations

Abstract

Rain in the atmosphere and impacts on the ocean surface lead to erroneous observations of the K/sub u/-band normalized radar cross section (NRCS) for the ocean surface, which is collected by orbiting Scatterometers. Rain can cause large errors in satellite-based estimates of the sea surface wind speed and direction derived from the affected data, depending on the surface wind speed and the rainrate. Rain within the radar beam results in attenuation and additive volume backscatter to the satellite. In order to correct each NRCS using a physically based electromagnetic model, the 3-D rain reflectivity must be measured throughout the satellite's K/sub u/-band beam with high resolution, and be nearly simultaneous with the satellite. Using satellite observations within the range of the NWS NEXRAD radars, these S-band data provide 2 km horizontal resolution and comparable vertical resolution, within 4 minutes of the satellite overpass. The correction technique also includes removal of the augmented surface roughness due to rain impacts. The surface wind vectors are then recalculated using the corrected NRCS, with the same wind-retrieval algorithm as that is used to produce the SeaWinds data product. Case studies will be presented that show the improved wind vector estimates over a significant area in several coastal regions, (the U.S. East Coast and the Gulf of Mexico), when comparing the corrected winds with the NCEP winds and buoy measurements.