Intensity and polarization of dust aerosols over polarized anisotropic surfaces

Abstract

The effect of surface polarization on the intensity and linear polarization patterns of sunlight in an atmosphere containing a dust aerosol layer is investigated by means of the adding principle for vector radiative transfer in which the surface is treated as a layer without transmission. We present a number of computational results and analysis for three cases: Lambertian (unpolarized isotropic), polarized isotropic, and polarized anisotropic surfaces. An approach has been developed to reconstruct anisotropic 2×2 phase matrix elements on the basis of bidirectional-reflectance and linear-polarization patterns that have been measured from polarimeters over various land surfaces. The effect of surface polarization on the simulated intensity patterns over a dust layer is shown to be negligible. However, the differences in the simulated linear polarization patterns between commonly assumed Lambertian and polarized anisotropic cases are substantial for dust optical depths between 0.1 and 0.5 and for surface albedos of 0.07 and 0.4, particularly in backward directions.