Hansen, J.E., 1969: Radiative transfer by doubling very thin layers. Astrophys. J., 155, 565-573, doi:10.1086/149892.
A doubling principle first used by van de Hulst has been developed to provide rapid and accurate results for the problem of diffuse reflection from a plane-parallel atmosphere. The method described here eliminates the need for numerically solving an equation of radiative transfer by beginning with a layer of such small optical thickness (τ ~ 2-25) that the initial scattering and transmission functions are given by the phase function. An application is made to spectral scattering by clouds in the visual and near-infrared, where the phase function is strongly peaked in the forward direction.