Rain Detection and Quality Control of SeaWinds

Abstract

A good assessment of the information content of scatterometer winds is particularly important in order to assimilate them in weather analysis. Besides retrieval problems in cases of a confused sea state, a particularly acute problem of Ku-band scatterometry is the sensitivity to rain. Elimination of poor quality data is therefore a prerequisite for the successful use of the National Aeronautics and Space Administration (NASA) Scatterometer (NSCAT) or QuikSCAT winds. Following the quality control for the European Remote-Sensing Satellite and NSCAT scatterometers performed at the Royal Netherlands Meteorological Institute, the authors further develop this methodology for QuikSCAT and define a quality indicator called the normalized residual (Rn). In order to characterize and validate the normalized residual, the authors use collocated Special Sensor Microwave Imager rain and European Centre for Medium-Range Weather Forecasts wind data. The results show indeed correlation between Rn and data quality. A wind speed dependent Rn threshold is shown to be adequate in terms of rejecting poor quality data (particularly rain) and keeping fair quality data. This opens the way to a quantitative use of SeaWinds measurements in weather analysis.