Fast RT Models

RTIASI

RTIASI is a fast radiative transfer model for the simulation of spectra as measured by the Infrared Atmospheric Sounding Interferometer (IASI). The spectra are sampled at 0.25 cm^-1 steps from 645 cm^-1 to 2760 cm^-1, resulting in 8461 “channels”. The transmittances used in RTIASI are based on accurate line-by-line calculations, convoluted with the IASI spectral response function. The model accounts for variable gas absorption by the molecules H₂O, CO₂, O₃, N₂O, CO, and CH₄. Other gas molecules are included at constant mixing ratio and vary only with air pressure. The radiative transfer is solved for an emitting and absorbing surface-atmosphere system, describing contributions by the upwelling emission from the atmosphere, the emission from the surface, the downwelling emission of the atmosphere reflected at the surface, and the reflected solar radiation. The current version of the model (RTIASI 4.0) solves the radiative transfer on a vertical grid defined by 90 pressure levels between 1050 and 0.005 hPa. Besides the direct model, adjoint, tangent-linear, and K-versions of the model have been prepared.

RTIASI was developed by ECMWF on behalf of EUMETSAT. The Fortran-90 program code can be made available for research purposes to non-commercial users. To obtain the software send a request for a license to EUMETSAT Legal Affairs Division (Am Kavalleriesand 31, D-64295 Darmstadt, Germany, Fax: +49 6151 807 425, Tel: +49 6151 807 7).

More scientific details are available from Marco Matricardi.

Radiative Transfer Software for NCEP Global Data Assimilation System (GDAS)

The redesign and rewrite of the radiative transfer code used in the NCEP Global Data Assimilation System (GDAS) has been completed and the code is in the testing stage, running in parallel with the operational model. The code was rewritten to allow for future expansion of it's capabilities, particularly with respect to the addition of addition channels (in preparation for the higher resolution IR sensors such as AIRS) and absorbing species, and to make the interface less susceptible to these changes when they are eventually introduced. A great deal of the differences are "under the hood" in that the user is not required to know a lot of interface details to make the use, maintenance, and upgrade of the code as simple and straightforward as possible. The beta release of the code is available at http://www.ssec.wisc.edu/~paulv/#F90_RTM.

Comparisons of the operational and parallel runs of the RT code can be found on the NCEP EMC Global Data Assimilation Group web page at http://sgi62.wwb.noaa.gov:8080/RTPUB by following the "Radiance Assimilation Monitoring" link.

OPTRAN

OPTRAN-6 Fit to LBLRTM
 

ITWG Working Group

Radiative Transfer and Surface Modeling