An Atmospheric radiative transfer model, code or simulator calculates radiative transfer of electromagnetic radiation through a planetary atmosphere, such as the Earth's.

## 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.[1] 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 80's - early 00's. Current (2011) project Continual Intercomparison of Radiation Codes emphasises also using observations to define intercomparison cases. [2]

## Table of models

Name
Website
References
UV
Visible
Near IR
Thermal IR
mm/sub-mm
Microwave
line-by-line/band
Scattering
Polarised
Geometry
Notes
4A/OP [1] Scott and Chédin (1981)

[3]

No No Yes Yes No No line-by-line ? ? freeware
6S/6SV1 [2] Kotchenova et al. (1997)

[4]

No Yes No No No No band ? Yes non-Lambertian surface
ARTS [3] Buehler et al. (2005)

[5]

No No No Yes Yes Yes line-by-line Yes Yes spherical 1D, 2D, 3D GPL
COART [4] Jin et al. (2006)

[6]

Yes Yes Yes Yes No No Yes No plane-parallel free
CRM [5] No Yes Yes ? No No ? ? freely available Part of NCAR Community Climate Model
CRTM [6] No Yes Yes Yes No Yes band Yes ?
DISORT [7] Stamnes et al. (1988)

[7]

Yes Yes Yes Yes No radar Yes No plane-parallel free with restrictions discrete ordinate, used by others
Fu-Liou [8] Fu and Liou (1993)

[8]

No Yes Yes ? No No Yes ? plane-parallel usage online, source code available web interface online at [9]
FUTBOLIN Martin-Torres (2005)

[9]

λ>0.3 µm Yes Yes Yes λ<1000 µm No line-by-line Yes ? spherical or plane-parallel handles line-mixing, continuum absorption and NLTE
GENLN2 [10] Edwards (1992)

[10]

? ? ? ? ? ? line-by-line ? ?
KARINE [11] Eymet (2005)

[11]

No No Yes No No ? ? plane-parallel GPL
KCARTA [12] ? ? Yes Yes ? ? line-by-line Yes ? plane-parallel freely available AIRS reference model
KOPRA [13] No No No Yes No No ? ?
LBLRTM [14] Clough et al. (2005)

[12]

Yes Yes Yes Yes Yes Yes line-by-line ? ?
LinePak [15] Gordley et al. (1994)

[13]

Yes Yes Yes Yes Yes Yes line-by-line No No spherical (Earth and Mars), plane-parallel freely available web interface, SpectralCalc
libRadtran [16] Mayer and Kylling (2005)

[14]

Yes Yes Yes Yes No No band or line-by-line Yes Yes plane-parallel or pseudo-spherical GPL
MATISSE [17] Caillault et al. (2007)

[15]

No Yes Yes Yes No No band Yes ? proprietary freeware
MODTRAN [18] Berk et al. (1998)

[16]

<50,000 cm-1 Yes Yes Yes Yes Yes band Yes ? proprietary commercial solar and lunar source, uses DISORT
MOSART [19] Cornette (2006)

[17]

λ>0.2 µm Yes Yes Yes Yes Yes band Yes No freely available
RFM [20] No No No Yes No No line-by-line ? ? available on request MIPAS reference model based on GENLN2
RRTM/RRTMG [21] Mlawer, et al. (1997)

[18]

<50,000 cm-1 Yes Yes Yes Yes >10 cm-1 ? ? free of charge uses DISORT
RTMOM [22] λ>0.25 µm Yes Yes λ<15 µm No No line-by-line Yes ? plane-parallel freeware
RTTOV [23] Saunders et al. (1999)

[19]

? ? ? ? ? ? band ? ? available on request
SBDART [24] Ricchiazzi et al. (1998)

[20]

Yes Yes Yes ? No No Yes ? plane-parallel uses DISORT
SCIATRAN [25] Rozanov et al. (2005)

[21]

Yes Yes Yes No No No Yes ? plane-parallel
SHARM Lyapustin (2002)

[22]

No Yes Yes No No No Yes ?
SHDOM [26] Evans (2006)

[23]

? ? Yes Yes ? ? Yes ?
Streamer, Fluxnet [27][28] Key and Schweiger (1998)

[24]

No No λ>0.6 mm λ<15 mm No No band Yes ? plane-parallel Fluxnet is fast version of STREAMER using neural nets
XRTM [29] Yes Yes Yes Yes Yes Yes Yes Yes plane-parallel and pseudo-spherical GPL
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 line width and the shape.

Name Author Description
HITRAN[25] Rothman et al. (1987, 1992, 1998, 2003, 2005, 2009) 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.
GEISA[26] 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.

## References

Footnotes
1. ^ R.W. Andrews, J.M. Pearce, The effect of spectral albedo on amorphous silicon and crystalline silicon solar photovoltaic device performance, Solar Energy, 91,233–241 (2013). DOI:10.1016/j.solener.2013.01.030 open access
2. ^ http://circ.gsfc.nasa.gov/
3. ^ Scott, N. A.; Chedin, A. (1981). "A fast line-by- line method for atmospheric absorption computations: The Automatized Atmospheric Absorption Atlas". J. Appl. Meteor. 20 (7): 802–812. Bibcode:1981JApMe..20..802S. doi:10.1175/1520-0450(1981)020<0802:AFLBLM>2.0.CO;2.
4. ^ Kotchenova, S. Y.; Vermote, E. F.; Matarrese, R; Klemm, F. J. (2006). "Validation of a vector version of the 6S radiative transfer code for atmospheric correction of satellite data. Part I: Path Radiance". Applied Optics 45 (26): 6762–6774. Bibcode:2006ApOpt..45.6762K. doi:10.1364/AO.45.006762. PMID 16926910.
5. ^ Buehler, S. A.; Eriksson, P.; Kuhn, T.; von Engeln, A.; Verdes, C. (2005). "ARTS, the Atmospheric Radiative Transfer Simulator". J. Quant. Spectrosc. Radiat. Transfer 91 (1): 65–93. Bibcode:2005JQSRT..91...65B. doi:10.1016/j.jqsrt.2004.05.051.
6. ^ Jin, Z.; Charlock, T.P.; Rutledge, K.; Stamnes, Y.; Wang (2006). "An analytical solution of radiative transfer in the coupled atmosphere-ocean system with rough surface". Appl. Opt. 45 (28): 7443–7455. Bibcode:2006ApOpt..45.7443S. doi:10.1364/AO.45.007443.
7. ^ Stamnes, Knut; Tsay, S. C.; Wiscombe, W.; Jayaweera, Kolf (1988). "Numerically stable algorithm for discrete-ordinate-method radiative transfer in multiple scattering and emitting layered media". Appl. Opt. 27 (12): 2502–2509. Bibcode:1988ApOpt..27.2502S. doi:10.1364/AO.27.002502.
8. ^ Fu, Q.; Liou, K.-N (1993). "Parameterization of the radiative properties of cirrus clouds". J. Atmos. Sci. 50 (13): 2008–2025. Bibcode:1993JAtS...50.2008F. doi:10.1175/1520-0469(1993)050<2008:POTRPO>2.0.CO;2.
9. ^ Martin-Torres, F. J.; Kutepov, A.; Dudhia, A.; Gusev, O.; Feofilov, A.G. (2003). "Accurate and fast computation of the radiative transfer absorption rates for the infrared bands in the atmosphere of Titan". Geophysical Research Abstracts: 7735. Bibcode:2003EAEJA.....7735M.
10. ^ 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.
11. ^ KARINE: a tool for infrared radiative transfer analysis in planetary atmospheres par V. Eymet. Note technique interne, Laboratoire d'Energétique, 2005.
12. ^ Clough, S. A.; Shephard, M. W.; Mlawer, E. J.; Delamere, J. S.; Iacono, M. J.; Cady-Pereira, K.; Boukabara, S.; Brown, P. D. (2005). "Atmospheric radiative transfer modeling: a summary of the AER codes". J. Quant. Spectrosc. Radiat. Transfer 91 (2): 233–244. Bibcode:2005JQSRT..91..233C. doi:10.1016/j.jqsrt.2004.05.058.
13. ^ Gordley, L. L.; Marshall, B. T. (1994). "LINEPAK: Algorithm for Modeling Spectral Transmittance and Radiance". J. Quant. Spectrosc. Radiat. Transfer 52 (5): 563–580. Bibcode:1994JQSRT..52..563C. doi:10.1016/0022-4073(94)90025-6.
14. ^ Mayer, B.; Kylling, A. (2005). "Technical note: The libRadtran software package for radiative transfer calculations - description and examples of use". Atmospheric Chemistry and Physics 5 (7): 1855–1877. doi:10.5194/acp-5-1855-2005.
15. ^ Caillaut, K.; Fauqueux, S.; Bourlier, C.; Simoneau, P.; Labarre, L. (2007). "Multiresolution optical characteristics of rough sea surface in the infrared". Applied Optics 46 (22): 5471–5481. Bibcode:2007ApOpt..46.5471C. doi:10.1364/AO.46.005471. PMID 17676164.
16. ^ Berk, A.; Bernstein, L. S.; Anderson, G. P.; Acharya, P. K.; Robertson, D. C.; Chetwynd, J. H.; Adler-Golden, S. M. (1998). "MODTRAN cloud and multiple scattering upgrades with application to AVIRIS". Remote Sensing of Environment (Elsevier) 65 (3,): 367–375. doi:10.1016/S0034-4257(98)00045-5.
17. ^ Cornette, William M. (2006). "Moderate Spectral Atmospheric Radiance and Transmittance (MOSART) Computer Code Version 2.00., Lexington, MA (2006)". Proc. IEEE-GRSS/AFRL Atmospheric Transmission Modeling Conference, Lexington MA.
18. ^ Mlawer, E. J.; Taubman, S. J.; Brown, P. D.; Iacono, M. J.; Claugh, S. A. (1997). "RRTM, a validated correlated-k model for the longwave". J. Geophys. Res. 102 (16): 663–682. Bibcode:1997JGR...10216663M. doi:10.1029/97JD00237.
19. ^ Saunders, R. W.; Matricardi, M.; Brunel, P. (1999). "An Improved Fast Radiative Transfer Model for Assimilation of Satellite Radiance Observations". Quart. J. Royal Meteorol. Soc. 125 (556): 1407–1425. Bibcode:1999QJRMS.125.1407S. doi:10.1256/smsqj.55614.
20. ^ Ricchiazzi, P.; Yang, S.; Gautier, C.; Sowle, D. (1998). "SBDART: A Research and Teaching Software Tool for Plane-Parallel Radiative Transfer in the Earth's Atmosphere". Bull. Am. Meteor. Soc. 79 (10): 2101–2114. Bibcode:1998BAMS...79.2101R. doi:10.1175/1520-0477(1998)079<2101:SARATS>2.0.CO;2.
21. ^ Rozanov, A.; Rozanov, V.; Buchwitz, M.; Kokhanovsky, A.; Burrows, J. P. (2005). "SCIATRAN 2.0-A new radiative transfer model for geophysical applications in the 175-2400 nm spectral region". Advances in Space Research (Elsevier) 36 (5): 1015–1019. Bibcode:2005AdSpR..36.1015R. doi:10.1016/j.asr.2005.03.012.
22. ^ Lyapustin, A. (2002). "Radiative transfer code SHARM-3D for radiance simulations over a non-Lambertian nonhomogeneous surface: intercomparison study". Applied Optics (OSA) 41 (27): 5607–5615. Bibcode:2002ApOpt..41.5607L. doi:10.1364/AO.41.005607. PMID 12269559.
23. ^ Evans, K. F. (1998). "The spherical harmonics discrete ordinate method for three-dimensional atmospheric radiative transfer". Journal of the Atmospheric Sciences 55 (3): 429–446. Bibcode:1998JAtS...55..429E. doi:10.1175/1520-0469(1998)055<0429:TSHDOM>2.0.CO;2.
24. ^ Key, J.; Schweiger, A. J. (1998). "Tools for atmospheric radiative transfer: Streamer and FluxNet". Computers & Geosciences 24 (5): 443–451. Bibcode:1998CG.....24..443K. doi:10.1016/S0098-3004(97)00130-1.
25. ^ HITRAN Site
26. ^ GEISA Site
General
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