Radiative transfer model for a spherical atmosphere.

Abstract

A new model for computing radiative transfer in a spherically symmetric atmosphere has been developed which uses a Gauss-Sidel iteration similar to Herman(1963). To account for inhomogeneities in the horizontal intensity field, the current work introduces a conical boundary on which solutions are found. This boundary is used in an interpolation scheme to obtain the intensity at the center of the cone. The model includes absorption and aerosols but neglects polarization and refraction. Checks of the model were performed. Results for a high sun and small optical depth compared to flat atmosphere results were consistent with geometric arguments. The results where the radius of the planet was increased by a factor of 100 agree with flat atmosphere results to better than 1%. Flux is conserved to better than 3%, and boundary solutions are accurate to better than 3% for nontangent paths, and 12% for tangent paths. A 10% biased boundary solution caused less than a 1% change in the final solution. The model also agreed favorably with models developed by Asous (1982), Marchuk et al. (1980) and Adams and Kattawar (1978). From the results of tests the model is concluded to be accurate to 3%, and in most earth-atmosphere situations accurate to 1%. This accuracy is on the order of, or better than, previous techniques and more computationally efficient than Monte Carlo simulations. The current model is more versatile and accurate than techniques that strive for computational efficiency. The model was used to examine the atmospheric limb problem and results from this work indicate that ozone and stratospheric dust layers may be detected from limb measurements.