Polarimetric scatterometry: A promising technique for improving ocean surface wind measurements from space

Spaceborne wind scatterometers provide useful measurements of ocean surface winds and are important to climatological studies and operational weather forecasting. Past and currently planned scatterometers use measurements of the copolarized backscatter cross-section at different azimuth angles to infer ocean surface wind speed and direction. Although successful, current scatterometer designs have limitations such as degraded wind performance in the near-nadir and outer regions of the measurement swath and a reliance on external wind information for vector ambiguity, removal, Theoretical studies of scattering from the mind-induced ocean surface indicate that polarimetric measurements provide orthogonal and complementary directional information to aid the wind retrieval process. In this paper, potential benefits of making polarimetric backscatter measurements to improve wind retrieval performance are addressed, To investigate the performance of a polarimetric scatterometer, a modified version of the SeaWinds end-to-end simulator at the Jet Propulsion Laboratory (JPL), Pasadena, CA, is employed, To model the effect of realistic measurement errors, expressions for polarimetric measurement variance and bias are derived. It is shown that a polarimetric scatterometer can be realized with straightforward and inexpensive modifications to a current scanning pencil-beam scatterometer system such as SeaWinds, Simulation results show that such a system can improve wind performance in the nadir region and eliminate the reliance on external wind information. The mechanism by which the addition of polarimetric measurements improves wind vector retrieval is discussed in detail. Field experiments are suggested to better characterize the polarimetric scattering properties of the wind-modulated ocean surface for future applications to wind scatterometry.