POLARIZED MICROWAVE EMISSION FROM WATER-WAVES

Partially polarimetric measurements of thermal emission from a striate d water surface at 91.65 GHz illustrate the potential for remote sensi ng of water wave direction by passive microwave radiometry. The three Stokes parameter measurements were made using a precision polarimetric radiometer trained on a rotatable water wave tank at several elevatio n angles from near nadir to near grazing. The polarimetric measurement s are well corroborated by calculations using a tilted-facet geometric al optics model for the water surface emission and scattering. Multipl e scattering of the incident background radiation is incorporated for observation angles approaching grazing. The downwelling background bri ghtness is computed by using an atmospheric radiative transfer model. We show that azimuthal brightness variations in the third Stokes param eter are in phase quadrature with the first and second modified Stokes parameters. For observation angles near similar to 60 degrees-70 degr ees from nadir the first three parameters have particularly large azim uthal brightness variations and thus have significant potential for me asuring ocean wave direction. Moreover, the azimuthal brightness varia tions caused by water waves are not negligible for many passive microw ave atmospheric sounding and surface remote sensing purposes, even at nadir. A range of elevation angles resulting in minimal azimuthal vari ations is identified.