Effects of anisotropic multiple scattering on solar radiation in the troposphere and stratosphere

Accurate determination of photodissociation rates in the troposphere and stratosphere in the 280-800-nm wavelength range requires calculation of the effects of anisotropic multiple scattering, pure absorption, and ground reflection on the solar flux incident at the top of the atmosphere. Past attempts to model these effects have led to approximate, sometimes time-consuming, models whose reliability is unknown. A general algorithm has been developed which includes (1) Rayleigh and Mie scattering by molecules and aerosols, (2) ground reflectivity, and (3) pure absorption by trace constituents such as ozone. Selected comparisons with existing approximate calculations are discussed, and a region of validity in wavelength and optical depth for isotropic scattering is presented.