Atmospheric transmittance of an absorbing gas 6 OPTRAN status report and introduction to the NESDIS/NCEP community radiative transfer model

Since the publication of the Optical Path Transmittance (OPTRAN) algorithm Appl. Opt. 34, 8396 (1995), much of the code and implementation has been refined and improved. The predictor set has been expanded, an objective method to select optimal predictors has been established, and the two-interpolation method has been discarded for a single-interpolation method. The OPTRAN coefficients have been generated for a wide range of satellites and instruments. The most significant new development is the Jacobian-K-matrix version of OPTRAN, which is currently used for operational direct radiance assimilation in both the Global Data Analysis System and the ETA Data Analysis System at the National Oceanographic and Atmospheric Administration, National Weather Service, National Centers for Environmental Prediction Environmental Modeling Center. This paper documents these improvements and serves as a record of the current status of the operational OPTRAN code.