Radiation geometry in the measurement and interpretation of radiation balance

Abstract The amount of radiation incident upon a radiometer depends on the shape of the radiometer surface, its orientation with respect to the sources of radiation, the distance between sources and radiometer, and other factors. The geometric factor describing the ratio of radiation received by the radiometer emanating from a particular source, to the total received from all sources (assumed to be radiating at the same rate) is the view factor. An intuitive approach is made to the development of the view factor, based on a presentation by Nusselt (1928). The view factor for a radiometer viewing the ground surface is shown graphically as an aid to determining appropriate heights for exposing instruments. Finally, a comparison of the short-wave radiation balance on a spherical and flatplate radiometer is made.