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 in fer ocean surface wind speed and direction. Although successful, current sc atterometer designs have limitations such as degraded wind performance in t he near-nadir and outer regions of the measurement swath and a reliance on external wind information for vector ambiguity, removal, Theoretical studie s of scattering from the mind-induced ocean surface indicate that polarimet ric measurements provide orthogonal and complementary directional informati on to aid the wind retrieval process. In this paper, potential benefits of making polarimetric backscatter measurements to improve wind retrieval perf ormance are addressed, To investigate the performance of a polarimetric sca tterometer, a modified version of the SeaWinds end-to-end simulator at the Jet Propulsion Laboratory (JPL), Pasadena, CA, is employed, To model the ef fect of realistic measurement errors, expressions for polarimetric measurem ent variance and bias are derived. It is shown that a polarimetric scattero meter can be realized with straightforward and inexpensive modifications to a current scanning pencil-beam scatterometer system such as SeaWinds, Simu lation results show that such a system can improve wind performance in the nadir region and eliminate the reliance on external wind information. The m echanism by which the addition of polarimetric measurements improves wind v ector retrieval is discussed in detail. Field experiments are suggested to better characterize the polarimetric scattering properties of the wind-modu lated ocean surface for future applications to wind scatterometry.