Anisotropic Solar Reflectance over White Sand, Snow and Stratus Clouds

Abstract

Integrated directional reflectances and relative anisotropy were measured over stratus clouds, snow and white gypsum sand using the Nimbus F-3 medium resolution radiometer (MRIR) and a siliconcell pyranometer mounted on a Piper Twin Comanche. Reflectances in the 0.2–4.0 and 0.55–0.85 μ portions of the solar spectrum were investigated. Eight flights were completed in different geographic areas over stratus clouds of varying thicknesses. Three flights were made over snow in two different localities and five flights were made over white sand found in the White Sands National Monument, N. Mex. The greatest anisotropy in scattered radiation was observed over stratus clouds. This anisotropy was composed of strong forward scattering and less pronounced backscattering. The anisotropy observed in the radiation reflected from snow was primarily due to specular reflection in the forward direction. Reflection back toward the sun was the predominant feature in the reflectance distributions observed over gypsum sand. The results demonstrate the interaction of the spectral reflectivity of the surface, the spectral response of the instrument, and the spectral character of the energy impinging upon the reflecting surface.