Computed Intensity and Polarization of Light Scattered Outwards from the Earth and an Overlying Aerosol

Abstract

Approximate numerical solutions to the equation of radiative transfer are calculated for two plane-parallel models composed of the earth’s atmospheric gas and aerosol particles. It is assumed that the incident illumination is parallel and that the light falling on the lower boundary at the earth’s surface is reflected according to Lambert’s law. The specific intensity and degree of polarization of the light emerging from the upper boundary of the models are given for the plane of the sun’s vertical as a function of the following parameters: solar nadir angle, direction of observation, ground reflectance, and wavelengths λ=0.503 and 0.625 μ. At these wavelengths the normal optical thicknesses of the two models are less than 0.26. The calculations show that the amount of radiation reflected from the ground is important for such moderate optical thickness. The degree of polarization and the rate that the intensity changes in the sun’s vertical plane decrease significantly when the reflectance of the ground increases from 0 to 0.25. Also, the differences between the specific intensities and between the degrees of polarization of the light scattered from the two models are small when the ground reflectance equals 0.25 or 0.80.