High resolution scatterometer wind processing

The launch of the Advanced Scatterometer ASCAT on MetOp-A is planned on 17 July 2006. Development of scatterometer products in Europe is organised through the EUMETSAT Satellite Application Facilities. Product developments are focussed on using the data for Numerical Weather Prediction and short-range weather forecasting. The former is well suited by the SeaWinds products as currently produced at KNMI at 100-km resolution (see http://www.knmi.nl/scatterometer ) in preparation of the operational ASCAT production suite. For short-range forecasting or in semi-enclosed sea areas such as the Mediteranean, however, higher resolution is desirable, and both an experimental 25-km SeaWinds product and the Early Advanced Retransmission Service, EARS, ERS-2 product are available. The European Space Agency ERS-2 scatterometer KNMI product provides quasi real-time winds in the North Atlantic and European seas. It is currently provided in the ASCAT BUFR format to facilitate the development of ASCAT user interfaces. KNMI attempts to improve the spatial filtering properties of the wind retrieval by using prior information on the expected meteorological balance, e.g., favouring rotational structures in high-latitude regions. Moreover, solutions in all wind directions, weighted by their inherent probability, are retained in the processing, the so-called Multi Solution Scheme. The 2D-VAR method has the advanced filtering properties needed for maintaining small-scale meteorological information in SeaWinds, while reducing noise. This is shown by comparing the autocorrelation of the KNMI products, with those of the NOAA SeaWinds product, and, for reference, those of the NCEP model. It is shown that scatterometer wind fields at high resolution contain noise, but that this noise is effectively removed in the Multi Solution Scheme. These findings will help KNMI to develop a 12.5-km ASCAT scatterometer wind product in the coastal zone in the next phase of the SAF project.