Passive Microwave Remote Sensing of Tropical Cyclones

Passive microwave radiometers have a strong heritage of instruments: the Special Sensor Microwave Imager (SSM/I), the Tropical Rainfall Mapping Mission (TRMM) Microwave Imager (TMI), the Advanced Microwave Scanning Radiometer–Earth Observing (AMSR-E) and the Special Sensor Microwave Imager/Sounder (SSMI/S). These instruments measure vertically and horizontally polarized brightness temperatures over a range of frequencies to retrieve parameters such as water vapor, sea-surface temperature, cloud liquid, rain, and near-surface ocean wind speed. The advent of microwave polarimetry offers the additional capability of passively measuring wind direction. WindSat, launched aboard Coriolis January 6, 2003, is the first satellite-based polarimetric radiometer (Gaiser et al. 2004). By measuring the full Stokes vector at 10.7, 18.7, and 37.0 GHz (as well as vertical and horizontal polarizations at 6.8 and 23.8 GHz), WindSat retrieves nearsurface ocean vector winds, along with water vapor, sea-surface temperature, cloud liquid, and precipitation. Since aircraft reconaissance flights of tropical cyclones are only deployed for systems that approach the east coast of the United States, direct satellite-based near-surface wind vector measurements offer a vital data source for monitoring the genesis of tropical cyclones (TCs). Space-based scatterometer passes only occur, at a minimum, every 12 hours. WindSat supplies much need coverage of ocean wind vectors, complementing space-borne scatterometers. This paper presents retrievals from the current WindSat Environmental Data (EDR) processing algorithm. The retrievals are an im-