An
Atmospheric radiative transfer model, code or simulator calculates
radiative transferRadiative transfer is the physical phenomenon of energy transfer in the form of electromagnetic radiation. The propagation of radiation through a medium is affected by absorption, emission and scattering processes. The equation of radiative transfer describes these interactions mathematically...
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
solverA solver is a generic term indicating a piece of mathematical software, possibly in the form of a standalone computer program or as a software library, that 'solves' a mathematical problem. A solver takes problem descriptions in some sort of generic form and calculate their solution...
such as a discrete ordinate method or a
Monte Carlo methodMonte Carlo methods are a class of computational algorithms that rely on repeated random sampling to compute their results. Monte Carlo methods are often used in computer simulations of physical and mathematical systems...
. 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
integrateIn numerical analysis, numerical integration constitutes a broad family of algorithms for calculating the numerical value of a definite integral, and by extension, the term is also sometimes used to describe the numerical solution of differential equations. This article focuses on calculation of...
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 lineA spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies. Types of line spectra :...
for all
moleculeA molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s in the atmospheric layer; this is called a
linebyline calculation.
For an instrument response, this is then
convolvedIn mathematics and, in particular, functional analysis, convolution is a mathematical operation on two functions f and g, producing a third function that is typically viewed as a modified version of one of the original functions. Convolution is similar to crosscorrelation...
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 precalculated coefficients (depending on
temperatureTemperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
and other parameters). In addition, models may consider
scatteringScattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized nonuniformities in the medium through which they pass. In conventional use, this also includes deviation of...
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
temperatureTemperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
or
humidityHumidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
).
Another common field of application is in a weather or climate model, where the
radiative forcingIn climate science, radiative forcing is generally defined as the change in net irradiance between different layers of the atmosphere. Typically, radiative forcing is quantified at the tropopause in units of watts per square meter. A positive forcing tends to warm the system, while a negative...
is calculated for
greenhouse gasA greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
es, aerosols or clouds. In such applications radiative transfer codes are often called
radiation parameterizationParameterization in a weather or climate model within numerical weather prediction refers to the method of replacing processes that are too smallscale or complex to be physically represented in the model by a simplified process. This can be contrasted with other processes—e.g., largescale flow of...
. 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



mm/submm

Microwave


Scattering

Polarised

Geometry

License

Notes


4A/OP 4A/OP or, Automatized Atmospheric Absorption Atlas,is an operational fast and accurate radiative transfer model for the infrared.4A/OP is a userfriendly software for various scientific applications , codeveloped by LMD and NOVELTIS with the support of CNES .NOVELTIS...

http://www.noveltis.fr/4AOP/ 
Scott and Chédin (1981) 






linebyline 



freeware 

6S/6SV1 6SV1 is an advanced radiative transfer code designed to simulate the reflection of solar radiation by a coupled atmospheresurface system for a wide range of atmospheric, spectral and geometrical conditions.It belongs to the group of procedures called...

http://6s.ltdri.org/ 
Kotchenova et al. (1997) 






band 




nonLambertian surface 
ARTS 
http://www.sat.ltu.se/arts/ 
Buehler et al. (2005) 






linebyline 


spherical 1D, 2D, 3D 
GPL 

CRM 
http://www.cgd.ucar.edu/cms/crm/ 











freely available 
Part of NCAR Community Climate Model 
CRTM Community Radiative Transfer Model is the fast radiative transfer model for calculations of radiances for satellite infrared or microwave nadir scanning radiometers ....

http://www.ssec.wisc.edu/~paulv/Fortran90/CRTM/Developmental/ 







band 





DISORT DISORT  general and versatile planeparallel radiative transfer program applicable to problems from the ultraviolet to the radar regions of the electromagnetic spectrum....

[ftp://climate1.gsfc.nasa.gov/wiscombe/Multiple_Scatt/] 
Stamnes et al. (1988) 









planeparallel 
free with restrictions 
discrete ordinate, used by others 
FuLiou 
http://snowdog.larc.nasa.gov/rose/fu200503/flp200503_web.htm 
Fu and Liou (1993) 









planeparallel 
usage online, source code available 
web interface online at http://snowdog.larc.nasa.gov/cgibin/rose/flp200503/flp200503.cgi 
FUTBOLIN FUTBOLIN : Multilevel multiple scattering radiative transfer model for the calculation of linebyline atmospheric emission/transmission spectra in planetary atmospheres. It has been developed by Javier MartinTorres FUTBOLIN (FUll Transfer By Optimized LINebyline methods): Multilevel multiple...


MartinTorres (2005) 






linebyline 


spherical or planeparallel 

handles linemixing, continuum absorption and NLTE 
GENLN2 See also:*List of atmospheric radiative transfer codes*Atmospheric radiative transfer codes*Absorption spectrum*MODTRAN*HITRANReferences:*Edwards, D. P. , GENLN2: A general linebyline atmospheric transmittance and radiance model, Version 3.0 description and users guide, NCAR/TN367STR,...

http://acd.ucar.edu/~edwards/ 
Edwards (1992) 






linebyline 





KARINE Karine may refer to:* Karine Bakhoum, an Egyptian American chef* Karine Costa , a French singer* Karine Haaland , a Norwegian comic strip creator* Karine Icher , a French professional golfer...

http://web.lmd.jussieu.fr/~eymet/karine.html 
Eymet (2005) 


colspan=2 





planeparallel 
GPL 

KCARTA 
http://asl.umbc.edu/pub/packages/kcarta.html 







linebyline 


planeparallel 
freely available 
AIRS The Atmospheric Infrared Sounder is one of six instruments flying on board NASA’s Aqua satellite, launched on May 4, 2002. The instrument is designed to support climate research and improve weather forecasting.... reference model 
KOPRA 
http://wwwimk.fzk.de/asf/ame/publications/kopra_docu/kopra_docu.html 













LBLRTM LBLRTM  The LineByLine Radiative Transfer Model is an accurate, efficient and highly flexible model for calculating spectral transmittance and radiance. See also :*List of atmospheric radiative transfer codes*Atmospheric radiative transfer codes...

http://rtweb.aer.com/lblrtm.html 
Clough et al. (2005) 






linebyline 





libRadtran 
http://www.libradtran.org/doku.php 
Mayer and Kylling (2005) 






band or linebyline 


planeparallel or pseudospherical 
GPL 

MATISSE 
http://matisse.onera.fr/index_english.htm 
Caillault et al. (2007) 






band 



propriety freeware 

MODTRAN MODTRAN is a computer program designed to model atmospheric propagation of electromagnetic radiation for the 10050,000 cm1 spectral range....

http://www.modtran.org/ 
Berk et al. (1998) 






band 



propriety commercial 
solar and lunar source, uses DISORT 
RFM 
http://www.atm.ox.ac.uk/RFM/ 







linebyline 



available on request 
MIPAS reference model based on GENLN2 
RRTM/RRTMG 
http://rtweb.aer.com/ 
Mlawer, et al. (1997) 










free of charge 
uses DISORT 
RTMOM 
[ftp://ftp.eumetsat.int/pub/MET/out/govaerts/RTMOMBETA/index.htm] 







linebyline 


planeparallel 
freeware 

RTTOV RTTOV  the fast radiative transfer model for calculations of radiances for satellite infrared or microwave nadir scanning radiometers ....

http://research.metoffice.gov.uk/research/interproj/nwpsaf/rtm/ 
Saunders et al. (1999) 






band 



available on request 

SBDART 
http://arm.mrcsb.com/sbdart/ 
Ricchiazzi et al. (1998) 









planeparallel 

uses DISORT 
SCIATRAN 
http://www.iup.unibremen.de/sciatran/ 
Rozanov et al. (2005) 









planeparallel 


SHARM 

Lyapustin (2002) 












SHDOM 
http://nit.colorado.edu/shdom.html 
Evans (2006) 












Streamer, Fluxnet FluxNet is a global network of micrometeorological tower sites that use eddy covariance methods to measure the exchanges of carbon dioxide, water vapor, and energy between the biosphere and atmosphere. Fluxnet is a global 'network of regional networks' that serves to provide an infrastructure to...

http://stratus.ssec.wisc.edu/streamer/streamer.htmlhttp://stratus.ssec.wisc.edu/fluxnet/ 
Key and Schweiger (1998) 






band 


planeparallel 

Fluxnet is fast version of STREAMER using neural netsAn artificial neural network , usually called neural network , is a mathematical model or computational model that is inspired by the structure and/or functional aspects of biological neural networks. A neural network consists of an interconnected group of artificial neurons, and it processes...

Name 
Website 
References 
UV 
VIS 
Near IR 
Thermal IR 
Microwave 
mm/submm 
linebyline/band 
Scattering 
Polarised 
Geometry 
License 
Notes 
Molecular absorption databases
For a linebyline calculation, one needs characteristics of the spectral lines, such as the line centre, the line width and the shape.
Name  Author  Description 
HITRAN HITRAN  HITRAN is a compilation of 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 compiled by the Air Force Cambridge Research Laboratories... 
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 HarvardSmithsonian Center for Astrophysics in Cambridge MA, USA. 
GEISA GEISA  GEISA is a computeraccessible spectroscopic database, designed to facilitate accurate forward radiative transfer calculations using a linebyline and layerbylayer approach... 
JacquinetHusson et al. (1999, 2005, 2008) 
GEISA (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Spectroscopic Information) is a computeraccessible spectroscopic database, designed to facilitate accurate forward radiative transfer calculations using a linebyline and layerbylayer 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 ScientifiqueFrance) 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
This article contains list of discrete dipole approximation codes and their applications.The discrete dipole approximation is a flexible technique for computing scattering and absorption by targets of arbitrary geometry. Given a target of arbitrary geometry, one seeks to calculate its scattering...
 Codes for electromagnetic scattering by cylinders
Codes for electromagnetic scattering by cylinders  this article list codes for electromagnetic scattering by a cylinder. Some of the source codes may be available on ....
 Codes for electromagnetic scattering by spheres
Codes for electromagnetic scattering by spheres  this article list codes for electromagnetic scattering by a homogeneous sphere, layered sphere, and cluster of spheres...
Light scattering
 Discrete dipole approximation codes
This article contains list of discrete dipole approximation codes and their applications.The discrete dipole approximation is a flexible technique for computing scattering and absorption by targets of arbitrary geometry. Given a target of arbitrary geometry, one seeks to calculate its scattering...
 Codes for electromagnetic scattering by cylinders
Codes for electromagnetic scattering by cylinders  this article list codes for electromagnetic scattering by a cylinder. Some of the source codes may be available on ....
 Codes for electromagnetic scattering by spheres
Codes for electromagnetic scattering by spheres  this article list codes for electromagnetic scattering by a homogeneous sphere, layered sphere, and cluster of spheres...