SOME QUALITIES OF SCATTERING FUNCTIONS DEFINING SKY RADIANCE DISTRIBUTIONS

The construction of empirical sky models necessary for the diffuse/sky irradiance calculations can respect theory and reality better when presuming the primary functional influences of the gradation and scattering redistribution of solar radiation within the atmosphere. The multiple scattering/diffusion and reflection caused by tiny particles of the, more or less, turbid atmosphere form the sky pattern which can be characterized by a radiance/luminance solid or its section, the scattering indicatrix. Model approximations of indicatrix functions are analyzed by using theoretical considerations or by deriving indicatrices from measured radiance sky scans. Advantages of applying the scattering indicatrix concept are documented by the comparison of measured, modelled, and calculated indicatrix courses.