Remote sensing of extreme events with satellite microwave sensors

Unprecedented views of surface wind and wave fields in tropical cyclones (TCs) are now provided respectively by the C-band (5.3 GHz) scatterometer and Synthetic Aperture Radar (SAR) on the European Remote Sensing Satellite-1 (ERS-1). Indeed, their signals at C-band are able to penetrate the thick convective clouds of these storms, observing the wind fields and directional wave spectra with good accuracy. Patterns of sea-state and surface wind are described and compared with the forecasting model of the European Center for Range Medium Weather Forecasts. It shows that this kind of strong mesoscale event are often missed by the model, mainly due to the lack of input data and because TC physics are not well understood. The use of microwave data allows greater confidence and greater temporal and spatial coverage for monitoring TCs over the open ocean. The combination of observations of different parameters by several sensors is necessary for two reasons: 1) in order to improve the understanding of feedback mechanism between the surface wind and heat fluxes that govern the development and behavior of TCs; 2) in order to know how the different parameters interact to modify the radar measurements (e.g. influence of sea-state and atmospheric water content on scatterometer wind measurements, and knowledge of the wind vector to resolve ambiguities in the wave directional spectrum as measured by the SAR). Improvements of the actual scatterometer system are discussed in order to define the best system for tropical cyclone monitoring in the future.<
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