Stability in SeaWinds Quality Control

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 very important for the successful use of the wind data of the SeaWinds instrument on QuikSCAT [1,2]. The process of discriminating between good and bad quality Wind Vector Cells (WVCs) winds is called Quality Control (QC). In the EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI SAF), wind products at 100-km and 25-km resolution are made in near-real time at KNMI. The processing is done using the SeaWinds Data Processor (SDP) software package. Input to the processing are the NOAA level 2 SeaWinds data in Binary Universal Form for the Representation of meteorological data (BUFR). Until now, the KNMI QC was based on the value of the Maximum Likelihood Estimator (MLE) [1-3] in the input product from NOAA. Since this input product will change in the near future, especially with regards to the formulation of the MLE [4], it is necessary to make the QC in the OSI SAF wind products independent of the MLEs as computed by NOAA. This report describes how the QC procedure is modified and made independent of the NOAA MLE with the aim to provide continuity in the KNMI SeaWinds wind product quality. The results of two new QC algorithms are compared with those of the old QC and it is shown that the best new QC algorithm performs even slightly better than the old one. The JPL rain flag in the NOAA product is also used in the KNMI QC. The rain flagging will also change and part of this report is devoted to the evaluation and possible reduction of its impact on the OSI SAF wind processing