Quality Control of Ku-band scatterometer winds

A good assessment of the information content of scatterometer winds is particularly important in order to assimilate them in weather analysis or use them in climate analyses. 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 very important for the successful use of the wind data of the OSCAT instrument on Oceansat-2 and the SeaWinds instrument on QuikSCAT. The process of discriminating between good and bad quality Wind Vector Cells (WVCs) winds is called Quality Control (QC).

The OSCAT instrument very much resembles the SeaWinds scatterometer which has been operational until November 23, 2009; it operates in the same frequency band and uses the same polarisations. KNMI has developed a QC mechanism for SeaWinds that is based on the wind inversion residual (MLE or Maximum Likelihood Estimator), which proved to be very effective in detecting rainy or otherwise distorted backscatter measurements. In this report, we assess the usability of this QC method for OSCAT and we propose some refinements in the algorithm that appear to be also profitable for SeaWinds.