Reflectance characteristics of uniform Earth and cloud surfaces derived from NIMBUS‐7 ERB

Abstract

Data from the scanning channels of the NIMBUS 7 Earth Radiation Budget (ERB) experiment are combined with other data on earth surface conditions and cloudiness. Patterns of bi‐directional reflectance are constructed from this data for uniform earth and cloud surfaces. Examples are shown that illustrate the bi‐directional properties of surfaces and how these properties vary with solar zenith angle (SZA). Dependence of albedo on SZA is also shown. Conclusions may be summarized as follows: (1) Water surfaces exhibit limb brightening at all SZAs; (2) cloud and land surfaces change from limb darkening to brightening as SZA increases; (3) the land surface exhibits higher backward reflection for SZAs less than about 50°; (4) all of the surfaces in this study become more specular as SZA increases; (5) snow is the most nearly isotropic of these surfaces; (6) snow albedo shows very little variation with SZA and even shows a slight decrease over a limited range; (7) albedo generally increases with increasing SZA for other than snow surfaces; (8) angular patterns for high water and ice clouds are quite similar, but ice clouds are more nearly isotropic; (9) the angular patterns developed in this study are in qualitative agreement with those from other investigations.