NCEP Radiative Transfer Model Status

Paul van Delst


The radiative transfer model (RTM) used in the NCEP GDAS system to estimate satellite channel radiances has been totally re-written in Fortran-90. The main goal of this effort was to provide an easily maintainable framework for future extensions (e.g. preparing for AIRS) and improvements to both the transmittance model algorithm (OPTRAN) and the radiative transfer module itself. In addition the software "refactoring" allowed for more robust tests of the numerical stability of the code across a number of different platforms. Some initial changes to the RTM include addition of the microwave cosmic background, using a diffusivity approximation for the downwelling thermal IR, and the implementation of a simple method to estimate the direct solar contribution for shortwave IR channels. The direction of future efforts will also be discussed.