An atmospheric radiative transfer model, code, or simulator calculates radiative transfer of electromagnetic radiation through a planetary atmosphere.

Methods

At the core of a radiative transfer model lies the radiative transfer equation that is numerically solved using a solver such as a discrete ordinate method or a Monte Carlo method. The radiative transfer equation is a monochromatic equation to calculate radiance in a single layer of the Earth's atmosphere. To calculate the radiance for a spectral region with a finite width (e.g., to estimate the Earth's energy budget or simulate an instrument response), one has to integrate this over a band of frequencies (or wavelengths). The most exact way to do this is to loop through the frequencies of interest, and for each frequency, calculate the radiance at this frequency. For this, one needs to calculate the contribution of each spectral line for all molecules in the atmospheric layer; this is called a line-by-line calculation. For an instrument response, this is then convolved with the spectral response of the instrument.

A faster but more approximate method is a band transmission. Here, the transmission in a region in a band is characterised by a set of pre-calculated coefficients (depending on temperature and other parameters). In addition, models may consider scattering from molecules or particles, as well as polarisation; however, not all models do so.

Applications

Radiative transfer codes are used in broad range of applications. They are commonly used as forward models for the retrieval of geophysical parameters (such as temperature or humidity). Radiative transfer models are also used to optimize solar photovoltaic systems for renewable energy generation. Another common field of application is in a weather or climate model, where the radiative forcing is calculated for greenhouse gases, aerosols, or clouds. In such applications, radiative transfer codes are often called radiation parameterization. In these applications, the radiative transfer codes are used in forward sense, i.e. on the basis of known properties of the atmosphere, one calculates heating rates, radiative fluxes, and radiances.

There are efforts for intercomparison of radiation codes. One such project was ICRCCM (Intercomparison of Radiation Codes in Climate Models) effort that spanned the late 1980s – early 2000s. The more current (2011) project, Continual Intercomparison of Radiation Codes, emphasises also using observations to define intercomparison cases.Continual Intercomparison of Radiation Codes

Table of models

Name Website References UV Visible mm/sub-mm Microwave /band Scattering Polarised Geometry License Notes 4A/OP Scott and Chédin (1981) band or line-by-line freeware 6S/6SV1 Kotchenova et al. (1997) band non-Lambertian surface ARTS Eriksson et al. (2011)

Buehler et al. (2018) line-by-line spherical 1D, 2D, 3D GPL BTRAM Chapman et al. (2009) line-by-line 1D, plane-parallel proprietary commercial COART Jin et al. (2006) plane-parallel freeCMFGENHillier (2020)line-by-line1D CRM band freely available Part of NCAR Community Climate Model CRTM Johnson et al. (2023) band 1D, Plane-Parallel Public Domain Fresnel ocean surfaces, Lambertian non-ocean surface DART radiative transfer model Gastellu-Etchegorry et al. (1996) band spherical 1D, 2D, 3D free for research with license non-Lambertian surface, landscape creation and import DISORT Stamnes et al. (1988) Lin et al. (2015) plane-parallel or pseudo-spherical (v4.0) free with restrictions discrete ordinate, used by others Eradiate band or line-by-line plane-parallel, spherical LGPL 3D surface simulation FARMS Xie et al. (2016) band plane-parallel free Rapidly simulating downwelling solar radiation at land surface for solar energy and climate research Fu-Liou Fu and Liou (1993) plane-parallel usage online, source code available web interface online: FUTBOLIN Martin-Torres (2005) line-by-line spherical or plane-parallel handles line-mixing, continuum absorption and NLTE GENLN2 Edwards (1992)Edwards, D. P. (1992), GENLN2: A general line-by-line atmospheric transmittance and radiance model, Version 3.0 description and users guide, NCAR/TN-367-STR, National Center for Atmospheric Research, Boulder, Co. line-by-line KARINE Eymet (2005)KARINE: a tool for infrared radiative transfer analysis in planetary atmospheres par V. Eymet. Note technique interne, Laboratoire d'Energétique, 2005.colspan=2 plane-parallel GPL KCARTA line-by-lineplane-parallelfreely available AIRS reference model KOPRA LBLRTM Clough et al. (2005) line-by-line LEEDR Fiorino et al. (2014) band or line-by-line spherical US government softwareextended solar & lunar sources; single & multiple scattering LinePak Gordley et al. (1994) line-by-line spherical (Earth and Mars), plane-parallelfreely available with restrictionsweb interface, SpectralCalc libRadtran Mayer and Kylling (2005) band or line-by-line plane-parallel or pseudo-spherical GPL MATISSE Caillault et al. (2007) band proprietary freewareMCARaTSGPL3-D Monte Carlo MODTRAN Berk et al. (1998) band or line-by-line proprietary commercial solar and lunar source, uses DISORT MOSART Cornette (2006) band freely available MSCART Wang et al. (2017) Wang et al. (2019) 1D, 2D, 3D available on requestPICASOlinkBatalha et al. (2019) Mukherjee et al. (2022)λ>0.3 μmband or correlated-kplane-parallel, 1D, 3DGPL Githubexoplanet, brown dwarf, climate modeling, phase-dependence Planetary Spectrum Generator (PUMAS) Villanueva (2018) Line-by-line and correlated-k plane-parallel and pseudo-spherical Free/online toolSolar system objects (planets, comets), exoplanets RADIS Pannier (2018)colspan=2 1D GPL RFM Dudhia (2017) line-by-line freely available on request MIPAS reference model based on GENLN2 RRTM/RRTMG Mlawer, et al. (1997) free of charge uses DISORT RTMOM line-by-line plane-parallel freeware RTTOV Saunders et al. (1999) band available on requestSASKTRANBourassa et al. (2008)

Zawada et al.

(2015) line-by-line spherical 1D, 2D, 3D, plane-parallelavailable on requestdiscrete and Monte Carlo options SBDART Ricchiazzi et al. (1998) plane-parallel uses DISORT SCIATRAN Rozanov et al. (2005) , Rozanov et al. (2014) band or line-by-line plane-parallel or pseudo-spherical or spherical SHARM Lyapustin (2002) SHDOM Evans (2006) σ-IASI Amato et al. (2002) Masiello et al. (2024) band, based on LBLRTM v12.4 plane-parallel Source code available online. Free for non commercial purposes. Analytical Jacobians. Complex treatment of aerosols/clouds with Tang scheme. SMART-G Ramon et al. (2019) band or line-by-line plane-parallel or spherical free for non-commercial purposes Monte-Carlo code parallelized by GPU (CUDA). Atmosphere or/and ocean options Streamer, Fluxnet FluxNet Key and Schweiger (1998) band plane-parallel Fluxnet is fast version of STREAMER using neural nets XRTM plane-parallel and pseudo-spherical GPL VLIDORT/LIDORT |-->] Spurr and Christi (2019) line-by-line VLIDORT only plane-parallel Used in SMART and VSTAR radiative transfer Name Website References UV VIS Near IR Thermal IR Microwave mm/sub-mm line-by-line/band Scattering Polarised Geometry License Notes

Molecular absorption databases

For a line-by-line calculation, one needs characteristics of the spectral lines, such as the line centre, the intensity, the lower-state energy, the line width and the shape.

Name Author Description HITRANHITRAN Site Rothman et al. (1987, 1992, 1998, 2003, 2005, 2009, 2013, 2017) HITRAN is a compilation of molecular spectroscopic parameters that a variety of computer codes use to predict and simulate the transmission and emission of light in the atmosphere. The original version was created at the Air Force Cambridge Research Laboratories (1960's). The database is maintained and developed at the Harvard-Smithsonian Center for Astrophysics in Cambridge MA, USA. GEISAGEISA Site Jacquinet-Husson et al. (1999, 2005, 2008) GEISA (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Spectroscopic Information) is a computer-accessible spectroscopic database, designed to facilitate accurate forward radiative transfer calculations using a line-by-line and layer-by-layer approach. It was started in 1974 at Laboratoire de Météorologie Dynamique (LMD/IPSL) in France. GEISA is maintained by the ARA group at LMD (Ecole Polytechnique) for its scientific part and by the ETHER group (CNRS Centre National de la Recherche Scientifique-France) at IPSL (Institut Pierre Simon Laplace) for its technical part. Currently, GEISA is involved in activities related to the assessment of the capabilities of IASI (Infrared Atmospheric Sounding Interferometer on board of the METOP European satellite) through the GEISA/IASI database derived from GEISA.

See also Discrete dipole approximation codes Codes for electromagnetic scattering by cylinders Codes for electromagnetic scattering by spheres Optical properties of water and ice

References Footnotes

General Bohren, Craig F. and Eugene E. Clothiaux, Fundamentals of atmospheric radiation: an introduction with 400 problems, Weinheim: Wiley-VCH, 2006, 472 p., . Goody, R. M. and Y. L. Yung, Atmospheric Radiation: Theoretical Basis. Oxford University Press, 1996 (Second Edition), 534 pages, . Liou, Kuo-Nan, An introduction to atmospheric radiation, Amsterdam; Boston: Academic Press, 2002, 583 p., International geophysics series, v.84, . Mobley, Curtis D., Light and water: radiative transfer in natural waters; based in part on collaborations with Rudolph W. Preisendorfer, San Diego, Academic Press, 1994, 592 p., Petty, Grant W, A first course in atmospheric radiation (2nd Ed.), Madison, Wisconsin: Sundog Pub., 2006, 472 p., Preisendorfer, Rudolph W., Hydrologic optics, Honolulu, Hawaii: U.S. Dept. of Commerce, National Oceanic & Atmospheric Administration, Environmental Research Laboratories, Pacific Marine Environmental Laboratory, 1976, 6 volumes. Stephens, Graeme L., Remote sensing of the lower atmosphere: an introduction, New York, Oxford University Press, 1994, 523 p. . Thomas, Gary E. and Knut Stamnes, Radiative transfer in the atmosphere and ocean, Cambridge, New York, Cambridge University Press, 1999, 517 p., . Zdunkowski, W., T. Trautmann, A. Bott, Radiation in the Atmosphere. Cambridge University Press, 2007, 496 pages,

External links ITWC for radiative transfer