Spectral Brightness of the Sky

Abstract

Knowledge of the brightness distribution of the daytime clear sky for different values of the atmospheric parameters is necessary for solving a number of applied problems. In twilight studies, for example, in order to take into account the influence of the troposphere, the brightness of the daytime clear sky must be known in absolute units for a large set of parameters. Experimental data on the brightness distribution make it possible to judge how close a particular model of the atmosphere used in theoretical calculations comes to reality. So far, however, there are no comprehensive tables of the spectral brightness of the daytime clear sky for a wide range of parameters, or even for the most important parameter — transmittance. The available results, for example, [1–3], were obtained only for a small set of parameters using visual and photoelectric photometers with wideband filters. In a number of cases, transmittance was not determined [2], and the results were given in relative units (readings from various points in the sky were tied to the zenith).