Fast radiative transfer model for simulation of infrared atmospheric sounding interferometer radiances.

A fast radiative transfer model has been developed for prelaunch simulation studies of Infrared Atmospheric Sounding Interferometer (IASI) data and for the exploitation of IASI radiances within the framework of a numerical weather prediction variational analysis scheme. The model uses profile-dependent predictors to parameterize the atmospheric optical depths and is fast enough to cope with the processing of observations in near real time and with the several thousands of transmittance calculations required to simulate radiances from a full range of atmospheric conditions. The development of the model has involved the selection of a training set of atmospheric profiles, the production of a line-by-line transmittance database, the selection of optimal predictors for the gases considered in the study, and the production of regression coefficients for the fast transmittance scheme. The model fit to the line-by-line radiances shows that it can reproduce the line-by-line radiances to a degree of accuracy that is at or below the instrumental noise.