REFERENCE FORWARD MODEL
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RFM v5.20 (20 Apr 2023)
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Further information
Also
- Atmospheric IR Atlas
- An intuitive (hopefully)
tool for working out which molecules might be
significant in any spectral region.
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Introduction
The RFM is a line-by-line radiative transfer model
developed at
AOPP,
Oxford University,
originally under an ESA contract to provide
reference spectral calculations for the
Envisat/MIPAS
instrument. It was largely built on GENLN2 algorithms.
It has subsequently been expanded into a general purpose code suitable for a
variety of different
spectroscopic calculations.
The main algorithm description is in the 2017 paper listed below under
Publications
The original code was written in FORTRAN77 but in 2018
RFM v5 was released,
rewritten in FORTRAN90.
The current version is compatible with
HITRAN 2020 and GEISA 2015 (as well as older versions).
RFM maintenance and development is currently supported by the
UK National Centre for Earth Observation
(NCEO).
The main design features are
- Easy to use — probably its main advantage
- Robustness — you shouldn't be able to crash the program
- Portability — written in (almost) standard FORTRAN90 and no external
libraries
- Self-documented code —
just in case you need to make you own modifications
- On-line documentation — these web pages
- Output spectra independent of spectral range
(eg value at 901.3 cm-1 will be the same whether you produce a spectrum from
901.2–901.4 cm-1 or from 500–1000 cm-1)
I'll consider adding other features that people would find useful, including
combinations of features which are currently not allowed. Just let me know,
along with any bug-reports.
To get a copy, email me with a brief statement on what you're planning on
using it for (which helps me to anticipate future user requirements)
and I'll email you the source code.
Anu Dudhia
( anu.dudhia@physics.ox.ac.uk )
Spectroscopic Data
The RFM is designed to use the three main types of HITRAN spectroscopic data
- Line-by-Line data (160-character .par files), providing the basic
parameters for each transition (wavenumber, intensity, Lorentz half-width
etc).
- Absorption Cross sections (.xsc files) representing
tabulations of k(ν,p,T)
where k is in cm2/molecule
- Collision Induced Absorption (.cia files) representing tabuluations of
c(ν,p,T) where c is in
cm5/molecule2
Additional HITRAN data sets such as HITEMP (line data) and UV
(cross-section data) can also used, with some care.
GEISA is an alternative to HITRAN, providing similar line and cross-section
data but in a different format.
While the RFM cannot use GEISA data directly,
local software is provided to convert these to HITRAN format.
Things the RFM can handle...
(Not all of these are compatible -
see User's Manual for the full
list of 'flags').
- Spherical or plane-parallel atmospheres, or homogeneous paths
[*TAN]
[More ...]
- Field-of-View
[*FOV]
& Instrument Line Shape
[*ILS]
convolutions
- CO2 Line mixing
[MIX]
- Continua for H2O, O2, N2 and CO2
[*GAS]
- Non-LTE (via user-supplied vibrational temperatures)
[NTE]
- Select lines of particular isotopes and/or bands
[*GAS]
- Jacobians (Weighting functions) for p, T, VMR,
line-of-sight pointing and
surface temperature and emissivity
[*JAC]
- Satellite/Balloon & Aircraft/Ground-based viewing geometries
[*OBS]
- Surface reflections
[*SFC]
- Output spectra of radiance
[RAD],
transmittance
[TRA],
absorption
[ABS],
cooling rates
[COO],
optical depth
[OPT],
brightness temperature
[BBT] and/or
Rayleigh-Jeans temperature
[RJT]
- Output diagnostics from ray-tracing (including Curtis-Godson integrations)
[PTH]
- Creation/Use of Look-Up Tables of
absorption coefficient k(ν,p,T)
[More ...]
- Horizontal structure in the atmosphere
[GRA]
- Flux calculations
[FLX]
and matrices.
[MTX]
- Different isotopic mixing ratio profiles
[*ATM]
- Extinction due to Rayleigh Scattering
[REX]
- Collision Induced Absorption data
[*CIA]
Things the RFM cannot handle...
- Sunlight (there is no 'sun' modelled in the RFM)
- Scattering (too difficult)
- Line-mixing other than CO2 (nearly there...)
- super-Voigt line parameters (nearly there...)
Publications
If you publish anything involving the RFM in the scientific literature
I do not expect to be a co-author, or even consulted. However,
I would appreciate it if you sent me a reference for the final publication since
it helps me obtain funding for RFM support.
If you want to cite the RFM, the following is recommended:
- Dudhia, A
- The
Reference Forward Model (RFM)
- Journal of Quantitative Spectroscopy and Radiative Transfer
- 186 (2017) 243–253
-
doi:10.1016/j.jqsrt.2016.06.018
Atmospheric, Oceanic and Planetary Physics
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