Linearization of a radiative transfer model in spherical geometry

Abstract

For the interpretation of satellite limb observations we investigate the linearization capability of spherical radiative transfer in the ultraviolet and visible part of the solar spectrum, where multiple scattering of light complicates the model simulations. From plane-parallel radiative transfer it is known that the forward-adjoint perturbation theory provides a powerful linearization tool. Its application to limb measurement simulations is the subject of this paper. First, we solve the scalar radiative transfer problem in spherical geometry in its forward and adjoint formulation. Subsequently, we apply the perturbation theory approach in the calculation of the derivatives of the intensity at the top of the atmosphere with respect to the absorption properties of a trace gas species in the case of a limb-viewing satellite instrument. The calculated derivatives are validated with a reference method, and the agreement in the upper atmosphere is very good, whereas deviations occur below the tangent height. Here the determination of the derivatives is clearly sensitive to the discretization of the problem. Finally, we perform an analysis for different viewing scenarios to characterize the capability of the described linearization approach.