SaskTran: A Radiative Transfer Tool for the Analysis of OSIRIS Measurements

The Optical Spectrograph and InfraRed Imager System (OSIRIS) makes measurements of limb scattered sunlight from 280 nm to 800 nm. These measurements are used to infer vertical number density profiles of multiple species including ozone, NO2 and aerosol extinctions. The calculations for the retrievals all involve a model of the OSIRIS signal and this is very computationally intensive. The SaskTran model has been developed as a fast yet accurate tool for this purpose. It uses a fully spherical geometry to model radiance contributions that include single Rayleigh and Mie scattering, a ground albedo term and a variable number of orders of multiple scatter. This paper will discuss the techniques involved in the development of SaskTran and will compare this model to others such as Limbtran and Modtran. Comparisons with actual OSIRIS measurements will also be included.