Additional terms of asymptotic expansions of the functions describing the scattered light in weakly media and the approximation relations for the reflective coefficient that essentially widen the applicability limits of asymptotics and simplify computations of these functions are obtained. Based on asymptotic formulas of the radiation transfer theory for the intensity of diffuse radiation at the boundaries of an optically thick scattering layer an expression for the parameter which describes actual absorption of light (s2 = (1 – L)/(3 – x1)) is derived. This relation, in combination with the formula for optical thickness of the layer, enables one to determine the volume scattering and absorption coefficients from measured intensity of radiation outgoing from the layer. The accuracy and applicability limits of the proposed formulas are investigated.