Parameterization of surface polarized reflectance derived from POLDER spaceborne measurements

Two months of spaceborne POLDER polarization measurements have been used to generate empirical surface bidirectional polarization distribution functions (BPDF's). Eleven surface classes have been defined based on a surface classification and a vegetation index, Within each class, the surface polarized reflectance was found rather homogeneous. The surface polarized reflectance is highly anisotropic and varies between 0 close to the backscattering direction, and a few percent in the forward scattering direction. For a given observation geometry, the polarization is about twice as large over the pixels classified as "desert" than over vegetated surfaces. An empirical function with two parameters fits the estimated surface polarized reflectance with a residue on the order of 10(-3) in reflectance units. An analysis of top-of-the-atmosphere (TOA) polarized reflectance over specific sunphotometer sites where the atmospheric contribution is well characterized confirms the estimated accuracy of 10(-3).