A FAST AND ACCURATE MODEL FOR MICROWAVE RADIANCE CALCULATIONS

A fast and accurate radiative transfer model was developed primarily f or microwave remote sensing and radiance data assimilation application s. Radiances at any direction were expressed by formal solution while the scattering source term was determined by a 4-stream discrete ordin ate solution using Henyey-Greenstein scattering phase function. The ac curacy of this model is analyzed by comparing it to a polarized 32-str eam discrete ordinate model with Mie scattering phase function, and an unpolarized 32-stream discrete ordinate model with Henyey-Greenstein scattering phase function. It shows that this model is fast and accura te enough for practical use in microwave remote sending and data assim ilation, the error being less than 3 K comparing to the accurate polar ized 32-stream model. It is also compared with a 2-stream Eddington mo del. The results show that it is more accurate than the Eddington mode l, especially for ice cloud conditions.