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In recent applications using an optical specular even detector (OSED I), a plane-polarimetric active-imaging system, results have shown that water surfaces supporting breaking gravity waves are efficient depolarizing scatterers at both microwave and visible wavelengths. Correlations of backscatter cross-section and degree-of-polarization with a polarimetric and range-gated radar at X-band wavelengths have shown good quantitative spatial and temporal agreement in laboratory experiments despite the great disparity in wavelengths. These correlations in conjunction with a temporally-synchronized side-looking camera have been crucial in the direct verification of conjectures concerning the scattering nature of ocean surfaces which have arisen from the study of ocean microwave backscatter experiments. In order to further understand the scattering process, a complete polarimetric characterization of the scattering surfaces is imperative. While advanced microwave systems presently provide full plane-polarization transmit-receive backscatter-cross-section matrices in horizontal and vertical polarization of the scene within the antenna footprint, a full Stokes-parameter description of a scattering scene is not easily obtained in the microwave regime. However, a Stokes-parameter imager at optical wavelengths appears to be feasible. We will discuss a new successor to our present OSED I to achieve this goal. OSED II will measure the four Stokes parameters using four CCD imagers viewing the same scene along the same optical axis via a single-aperture four-imager prism camera system. Appropriately chosen polarization filters in front of each imager will provide the polarimetric analysis capability. This instrument will allow the unambiguous specification of the orientation of the plane polarized component, and allow experimental assessment of the importance of any unpolarized component and of the possibility of any circularly polarized component. The complete Stokes parameter characterization of the breaking wave as a scattering surface will provide important information to guide the interpretation of microwave backscatter from ocean surfaces. The OSED II detection system will also be applicable to the general polarimetric description of remotely sensed scattering surfaces.
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