Atmospheric radiative transfer codes

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). 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 effeorts 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.

Table of models

Name	Website	References	UV	Visible	Near IR	Thermal IR	mm/sub-mm	Microwave	line-by-line/band	Scattering	Polarised	Geometry	License	Notes
4A/OP	[1]	Scott and Chédin (1981)	No	No	Yes	Yes	No	No	line-by-line	?	?		freeware
6S/6SV1	[2]	Kotchenova et al. (1997)	No	Yes	No	No	No	No	band	?	Yes			non-Lambertian surface
ARTS	[3]	Buehler et al. (2005)	No	No	No	Yes	Yes	Yes	line-by-line	Yes	Yes	spherical 1D, 2D, 3D	GPL
CRM	[4]		No	Yes	Yes	?	No	No		?	?		freely available	Part of NCAR Community Climate Model
CRTM	[5]		No	Yes	Yes	Yes	No	Yes	band	Yes	?
DISORT	[6]	Stamnes et al. (1988)	Yes	Yes	Yes	Yes	No	radar		Yes	?	plane-parallel	free with restrictions	discrete ordinate, used by others
Fu-Liou	[7]	Fu and Liou (1993)	No	Yes	Yes	?	No	No		Yes	?	plane-parallel	usage online, source code available	web interface online at [8]
FUTBOLIN		Martin-Torres (2005)	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	[9]	Edwards (1992)	?	?	?	?	?	?	line-by-line	?	?
KARINE	[10]	Eymet (2005)	No	No	Yes		No	No		?	?	plane-parallel	GPL
KCARTA	[11]		?	?	Yes	Yes	?	?	line-by-line	Yes	?	plane-parallel	freely available	AIRS reference model
KOPRA	[12]		No	No	No	Yes	No	No		?	?
LBLRTM	[13]	Clough et al. (2005)	Yes	Yes	Yes	Yes	Yes	No	line-by-line	?	?
libRadtran	[14]	Mayer and Kylling (2005)	Yes	Yes	Yes	Yes	No	No	band or line-by-line	Yes	Yes	plane-parallel or pseudo-spherical	GPL
MATISSE	[15]	Caillault et al. (2007)	No	Yes	Yes	Yes	No	No	band	Yes	?		propriety freeware
MODTRAN	[16]	Berk et al. (1998)	ṽ<50,000 cm-1	Yes	Yes	Yes	Yes	Yes	band	Yes	?		propriety commercial	solar and lunar source, uses DISORT
RFM	[17]		No	No	No	Yes	No	No	line-by-line	?	?		available on request	MIPAS reference model based on GENLN2
RRTM/RRTMG	[18]	Mlawer, et al. (1997)	ṽ<50,000 cm-1	Yes	Yes	Yes	Yes	ṽ>10 cm-1		?	?		free of charge	uses DISORT
RTMOM	[19]		λ>0.25 µm	Yes	Yes	λ<15 µm	No	No	line-by-line	Yes	?	plane-parallel	freeware
RTTOV	[20]	Saunders et al. (1999)	?	?	?	?	?	?	band	?	?		available on request
SBDART	[21]	Ricchiazzi et al. (1998)	Yes	Yes	Yes	?	No	No		Yes	?	plane-parallel		uses DISORT
SCIATRAN	[22]	Rozanov et al. (2005)	Yes	Yes	Yes	No	No	No		Yes	?	plane-parallel
SHARM		Lyapustin (2002)	No	Yes	Yes	No	No	No		Yes	?
SHDOM	[23]	Evans (2006)	?	?	Yes	Yes	?	?		Yes	?
Streamer, Fluxnet	[24][25]	Key and Schweiger (1998)	No	No	λ>0.6 mm	λ<15 mm	No	No	band	Yes	?	plane-parallel		Fluxnet is fast version of STREAMER using neural nets
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	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	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 over three decades 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

• ITWC for radiative transfer
• Discrete dipole approximation codes
• Codes for electromagnetic scattering by cylinders
• Codes for electromagnetic scattering by spheres

See also

Light scattering

• Discrete dipole approximation codes
• Codes for electromagnetic scattering by cylinders
• Codes for electromagnetic scattering by spheres

Refractive index

• Optical properties of water and ice

References

• Bohren, Craig F. and Eugene E. Clothiaux, Fundamentals of atmospheric radiation: an introduction with 400 problems, Weinheim : Wiley-VCH, 2006, 472 p., ISBN 3-527-40503-8.

• Goody, R. M. and Y. L. Yung, Atmospheric Radiation: Theoretical Basis. Oxford University Press, 1996 (Second Edition), 534 pages, ISBN 978-0-19-510291-8.

• Liou, Kuo-Nan, An introduction to atmospheric radiation, Amsterdam ; Boston : Academic Press, 2002, 583 p., International geophysics series, v.84, ISBN 0-12-451451-0.

• 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., ISBN 0-12-502750-8

• Petty, Grant W, A first course in atmospheric radiation (2nd Ed.), Madison, Wisconsin : Sundog Pub., 2006, 472 p., ISBN 0-9729033-1-3

• 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. ISBN 0-19-508188-9.

• Thomas, Gary E. and Knut Stamnes, Radiative transfer in the atmosphere and ocean, Cambridge, New York, Cambridge University Press, 1999, 517 p., ISBN 0-521-40124-0.

• Zdunkowski, W., T. Trautmann, A. Bott, Radiation in the Atmosphere. Cambridge University Press, 2007, 496 pages, ISBN 9780521871075