Atmospheric radiative transfer codes
Encyclopedia
An Atmospheric radiative transfer model, code or simulator calculates radiative transfer
of electromagnetic radiation through a planetary atmosphere, such as the Earth's.
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 molecule
s 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.
or humidity
).
Another common field of application is in a weather or climate model, where the radiative forcing
is calculated for greenhouse gas
es, 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.
Radiative transfer
Radiative 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 solverSolver (computer science)
A solver is a generic term indicating a piece of mathematical software, possibly in the form of a stand-alone 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 method
Monte Carlo method
Monte 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 integrate
Numerical integration
In 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 line
Spectral line
A 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 molecule
Molecule
A 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 line-by-line calculation.
For an instrument response, this is then convolved
Convolution
In 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 cross-correlation...
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
Temperature
Temperature 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 scattering
Scattering
Scattering 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 non-uniformities 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
Temperature 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 humidity
Humidity
Humidity 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 forcing
Radiative forcing
In 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 gas
Greenhouse gas
A 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 parameterization
Parametrization (climate)
Parameterization in a weather or climate model within numerical weather prediction refers to the method of replacing processes that are too small-scale or complex to be physically represented in the model by a simplified process. This can be contrasted with other processes—e.g., large-scale 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/sub-mm |
Microwave |
Scattering |
Polarised |
Geometry |
License |
Notes |
|||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 4A/OP 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 user-friendly software for various scientific applications , co-developed by LMD and NOVELTIS with the support of CNES .NOVELTIS... |
http://www.noveltis.fr/4AOP/ | Scott and Chédin (1981) | line-by-line | freeware | ||||||||||
| 6S/6SV1 6S (radiative transfer code) 6SV1 is an advanced radiative transfer code designed to simulate the reflection of solar radiation by a coupled atmosphere-surface 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 | non-Lambertian surface | ||||||||||
| ARTS | http://www.sat.ltu.se/arts/ | Buehler et al. (2005) | line-by-line | 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 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 DISORT - general and versatile plane-parallel 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) | plane-parallel | free with restrictions | discrete ordinate, used by others | |||||||||
| Fu-Liou | http://snowdog.larc.nasa.gov/rose/fu200503/flp200503_web.htm | Fu and Liou (1993) | plane-parallel | usage online, source code available | web interface online at http://snowdog.larc.nasa.gov/cgi-bin/rose/flp200503/flp200503.cgi | |||||||||
| FUTBOLIN FUTBOLIN FUTBOLIN : Multi-level multiple scattering radiative transfer model for the calculation of line-by-line atmospheric emission/transmission spectra in planetary atmospheres. It has been developed by Javier Martin-Torres FUTBOLIN (FUll Transfer By Optimized LINe-by-line methods): Multi-level multiple... |
Martin-Torres (2005) | line-by-line | spherical or plane-parallel | handles line-mixing, continuum absorption and NLTE | ||||||||||
| GENLN2 GENLN2 -See also:*List of atmospheric radiative transfer codes*Atmospheric radiative transfer codes*Absorption spectrum*MODTRAN*HITRAN-References:*Edwards, D. P. , GENLN2: A general line-by-line atmospheric transmittance and radiance model, Version 3.0 description and users guide, NCAR/TN-367-STR,... |
http://acd.ucar.edu/~edwards/ | Edwards (1992) | line-by-line | |||||||||||
| KARINE 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 | plane-parallel | GPL | |||||||||
| KCARTA | http://asl.umbc.edu/pub/packages/kcarta.html | line-by-line | plane-parallel | freely available | AIRS Atmospheric Infrared Sounder 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 |
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| KOPRA | http://www-imk.fzk.de/asf/ame/publications/kopra_docu/kopra_docu.html | |||||||||||||
| LBLRTM LBLRTM LBLRTM - The Line-By-Line 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) | line-by-line | |||||||||||
| libRadtran | http://www.libradtran.org/doku.php | Mayer and Kylling (2005) | band or line-by-line | plane-parallel or pseudo-spherical | GPL | |||||||||
| MATISSE | http://matisse.onera.fr/index_english.htm | Caillault et al. (2007) | band | propriety freeware | ||||||||||
| MODTRAN MODTRAN MODTRAN is a computer program designed to model atmospheric propagation of electromagnetic radiation for the 100-50,000 cm-1 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/ | line-by-line | 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/RTMOM-BETA/index.htm] | line-by-line | plane-parallel | freeware | ||||||||||
| RTTOV RTTOV (radiative transfer code) 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) | plane-parallel | uses DISORT | ||||||||||
| SCIATRAN | http://www.iup.uni-bremen.de/sciatran/ | Rozanov et al. (2005) | plane-parallel | |||||||||||
| SHARM | Lyapustin (2002) | |||||||||||||
| SHDOM | http://nit.colorado.edu/shdom.html | Evans (2006) | ||||||||||||
| Streamer, Fluxnet 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 | plane-parallel | Fluxnet is fast version of STREAMER using neural nets Artificial neural network An 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... |
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| 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 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 Harvard-Smithsonian Center for Astrophysics in Cambridge MA, USA. |
| GEISA GEISA GEISA - GEISA is a computer-accessible spectroscopic database, designed to facilitate accurate forward radiative transfer calculations using a line-by-line and layer-by-layer approach... |
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 codesDiscrete dipole approximation codesThis 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 cylindersCodes for electromagnetic scattering by cylindersCodes 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 spheresCodes for electromagnetic scattering by spheresCodes 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 codesDiscrete dipole approximation codesThis 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 cylindersCodes for electromagnetic scattering by cylindersCodes 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 spheresCodes for electromagnetic scattering by spheresCodes for electromagnetic scattering by spheres - this article list codes for electromagnetic scattering by a homogeneous sphere, layered sphere, and cluster of spheres...