Fast Infrared Radiative Transfer Model for ATSR

摘要

There is a continuing trend towards the use of variational methods in satellitedata interpretation. In these methods, the difference between measured radiances and those calculated from a particular atmosheric 'state' is minimized by making suitable adjustments to the 'state' until agreement is within what can be loosely called the system noise level. For this method to be feasible the radiance calculation, using the forward model, has to be computatonally fast; full line by line methods are far too slow. The paper describes a fast transmittance model for ATSR channels. It is based very closely on a model used by the European Centre for Medium Range Weather Forecasts for TIROS Operational Vertical Sounder (TOVS) measurements. A line by line model is modified to calculate a base set of channel transmittances for a wide ranging set of atmospheric profiles. These are used to generate the fast model coefficients. It is found that the predictors used for the TOVS instrument channels are not optimal for ATSR channels and significant improvements are made by changes to the water transmittance terms.