Impact of rain on spaceborne Ku-band wind scatterometer data

The accuracy of Ku-band ocean wind scatterometers (i.e., NSCAT and SeaWinds) is impacted to varying degrees by rain. In order to determine how to best flag rain-contaminated wind vector cells and ultimately to calibrate out the effects of rain as much as possible, we must understand the impact of rain on the backscatter measurements that are used to retrieve wind vectors. This study uses collocated SSM/I rain rate measurements, NCEP wind fields, and SeaWinds on QuikSCAT backscatter measurements to empirically fit a simple theoretical model of the effect of rain on sigma(o), and to check the validity of that model. The chief findings of the study are 1) horizontal polarization measurements are more sensitive to rain than vertical polarization, 2) sensitivity to rain varies dramatically with wind speed, and 3) the additional backscatter due to rain overshadows the rain-related attenuation.