Spherical Radiative Transfer Model with Computation of Layer Air Mass Factors and Some of Its Applications

A radiative transfer model was designed for use in inverse problems of atmospheric optics. The model calculates intensities and their derivatives with respect to absorption. In other notations, these derivatives are known as weighting functions or layer air mass factors. Multiple scattering radiation in the model is evalu- ated by the Monte Carlo method. Radiative transfer is simulated for a spherical shell atmosphere taking into account polarization, Rayleigh and aerosol scattering, gas and aerosol absorption, and Lambert surface albedo. The speed of intensity computations accurate to 1% is approximately the same as in other authors' pseudospher- ical models used for comparison. The time required for simultaneous computation of intensities and their deriv- atives is only 1.2-1.8 times as much as the time required for the computation of intensities alone. The model was compared with other spherical and pseudospherical models for geometries in which the sphericity of the atmosphere is important: twilight observations from the ground and limb scatter observations from space. The layer air mass factors calculated by different models were also compared. The influence of approximate (single scattering) computation of weighting functions on the accuracy of ozone profile retrievals was investigated for the Umkehr method used as an example. It was shown that the single scattering approximation gives additional large retrieval errors.