Detecting rain with QuikScat

The wind retrievals produced from the QuikScat Scatterometer[1] are affected by the presence of rain. Scattering from the rain drops and from surface roughness caused by rain-induced splashing increases the measured signal power. The rain also attenuates the signal as it travels to and from the sea surface, reducing its power. At low wind speeds, the scattering effects dominate, causing the inferred wind-induced radar cross-section and therefore the wind speed to be over estimated. At high winds, attenuation becomes more important. In order to detect rain-contaminated winds, we have developed a rain-detection algorithm based on how well the measured radar crosssections fit the NSCAT-2 model function[2] that was used to retrieve the winds. We report an analysis of the performance of our algorithm. At low wind speeds, our algorithm may be a more sensitive measure of rain than microwave-radiometer-based methods. We also report the results of a study where we attempt to use QuikScat measurements, in conjunction with winds modeled by a general circulation model, to deduce rain rates over the world's oceans.