Polarized reflectance of bare soils and vegetation: measurements and models

This paper presents a large set of spectral and directional signatures of the polarized reflectance acquired over various surfaces. Two analytical physically-based models were developed, one for bare soils and the other for simple vegetation cover. They consider that the polarized reflectance is generated by single specular reflection over isotropically distributed facets or leaves. The models accurately reproduce the order of magnitude and the directional signature of the reflectance for view angles of up to ~ 5 5 "I.t confirms that specular reflection is the main process that generates polarization over natural surfaces. Polarized light generated by other processes, and that are not accounted for by the models, can be observed however in the backscattering direction where single specular reflection does not yield polarization. Although spectral variations in the polarized reflectance are observed, they are explained by atmospheric effects on the direct solar beam. The atmospheric correction yields a surface polarized reflectance which is larger than the model estimate, but is still on the same order of magnitude. For the simple canopies studied, our results suggest that, except for particular events such as the "heading" of a canopy, vegetation will generate little variability in the polarized reflectance making this information unsuitable for monitoring of the canopies. On the other hand, since the models accurately predict the polarized reflectance from the surface, they can be used to correct airborne or spaceborne polarized reflectance measurements when the inversion of aerosol parameters is attempted.