Maintaining and developing fast radiative transfer models in support of satellite data interpretation, processing and assimilation into the Unified Model
In order to simulate the upwelling radiance measured by a satellite instrument (e.g. for a near nadir viewing sounder like AMSU), the electromagnetic radiation emitted or absorbed by gases along the viewing path, and from the surface and/or cloud, must be computed. For radiance assimilation in an NWP model, this calculation must be made in a few milliseconds for all the radiance channels in order not to delay the production of the model forecast. Hence, the development of fast radiative transfer models is an important activity to enable assimilation of satellite radiances within the Met Office NWP models.
The RTTOV model is currently used to carry out rapid radiative transfer calculations for all the meteorological satellite instruments of current interest in the Met Office. The present version of RTTOV (RTTOV-9) can simulate radiances for many different sensors, and has been developed under the EUMETSAT-funded NWP Satellite Application Facility, with the Met Office, Météo-France and ECMWF all contributing to its development.
With more and more data from high resolution infrared sounders (e.g. AIRS and IASI) becoming available, new techniques need to be investigated if we are to simulate efficiently the thousands of available channels. In addition, developments in the knowledge of atmospheric spectroscopic parameters and techniques of line-by-line modelling need to be monitored, in order to incorporate these improvements into RTTOV.