Polarimetric Microwave Radiometer Architectures and Characterization for Spaceborne Mapping of Ocean Surface Wind Vector

Global mapping of ocean surface wind vector (OSWV) is crucial for many oceanographic and atmospheric studies, as well as civil and military operations. Since 2003, the WindSat instrument, which is a satellite based polarimetric microwave radiometer, has been the sole operational work horse for providing OSWV data as input to numerical weather prediction models of the U.S. Navy and NOAA. However, with WindSat expecting to reach its projected end-of-life by 2015 and no other systems to take its place, a critical gap in OSWV capability is looming.

Currently, the Special Sensor Microwave Imager Sounder (SSMIS) instrument built by NGES in the Azusa campus provides global wind speed data to the users. The principle of operation makes use of the 1st and 2nd Stokes parameters of the elliptically polarized microwave emissions from the sea surface. The elliptical polarization is the result of wind-induced water ripples which appear smoother in the crosswind direction and rougher in the up- or downwind direction. In order to obtain information about wind direction, knowledge of the 3rd and 4th Stokes parameters is necessary.

In this presentation, we will review the principles of microwave polarimetry and its applications, followed by a description of several polarimetric receiver architectures for wind direction detection. We will describe how these receiver architectures can conceptually be incorporated into the present SSMIS system while at the same time preserving most of the existing capabilities. The advantages of such an approach are low risk, lower cost, and better timeliness in filling the OSWV capability gap.