Gastropod - a fast radiative transfer model for AIRS and IASI User Guide
SHERLOCK, Vanessa
Gastropod is a fast radiative transfer code developed to meet the requirements for a day-one radiative transfer operator for AIRS (and eventually IASI) for use in variational data assimilation systems. Forward model formulation is based principally on the PFAAST AIRS model developed by Hannon et al. Separate prediction of water vapour line and continuum absorption has been adopted based on the performance of the PFAAST model in the H2O nu 2 band and the longwave window regions. However, a single case prediction scheme for water vapour line absorption has been implemented so as to avoid errors (discontinuitie?s) in modelled Jacobians associated with transitions between regression schemes. The interface for profile input has also been generalised to allow mean parameters used in the effective optical depth prediction scheme and the radiative transfer (RT) calculation has been modified to ensure a well-defined adjoint mapping from RT layer mean quantities to input profile variables in all situations. Finally, Gastropod makes an important extension to the PFAAST model, as tangent linear and K models have also been coded and validated. The ...
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