Coefficients for RTTOV v11

• Latest version of rttov_const.F90
• General information about coefficient files
• Changes to instrument IDs and names since RTTOV v10
• How to convert between coefficient file formats and extract channel subsets


• Script for downloading coefficient files (run from within rtcoef_rttov11/ directory)
• Download Hi-res IR sounder coefficients
• Download IR sensor coefficients
• Download Visible/IR solar-compatible coefficients
• Download MW sensor coefficients


• History log of coefficient file changes
• Spectral response functions/pass-bands
• Comparisons against LBL simulations


• Coefficient regression limits

• 18/02/2016 - add Mietable files for MWS and MWI (under MW instruments).
• 20/01/2016 - add coefficients for INSAT3-D imager and sounder instruments (under IR instruments).
• 19/11/2015 - add coefficients for MWR instrument (under MW instruments).
• 17/11/2015 - add coefficients for ECOSTRESS instrument on the ISS (under IR instruments).
• 16/11/2015 - updates to v9 predictor coefficients for AVHRR on Metop and NOAA 15-18, VISSR on FY2-3 and 4, ASTER and VIIRS: non-solar channels are now only trained over the more limited range of zenith angles up to 65 degrees (under VIS/IR instruments).
• 08/10/2015 - new Sentinel-3 SLSTR coefficients with updated SRFs (under VIS/IR instruments and IR instruments).
• 25/09/2015 - new PC-RTTOV coefficients valid over all surface types for RTTOV v11.3 (under hi-res IR instruments).
• 25/09/2015 - all IR and MW v7/v8 predictor coefficients regenerated with bugs fixed in coefficient generation. (NB Work is underway to generate new Zeeman coefficients; the AMSU-A shifted coefficients are under review and have not been regenerated; v9 predictor and SSU coefficients are unaffected and have not been regenerated).
• 25/09/2015 - MODIS and FY-3 IRAS coefficients updated with some channels now being Planck-weighted (under VIS/IR instruments and IR instruments).
• 17/07/2015 - add Jason-2 AMR coefficients (under MW instruments).
• 10/07/2015 - add Nimbus-3 MRIR coefficients (under IR instruments).
• 09/07/2015 - add SSM/T2 coefficients (under MW instruments).
• 09/07/2015 - add MetopSG preliminary ICI coefficients (under MW instruments).
• 08/07/2015 - add MetopSG MetImage coefficients (under VIS/IR instruments and IR instruments).
• 03/07/2015 - add MetopSG MWI and MWS coefficients (under MW instruments).
• 24/06/2015 - Nimbus 4 IRIS coefficients updated with coefficients for full spectral range (under hires).
• 05/03/2015 - add F-19 SSMIS coefficient file (under MW instruments).
• 25/02/2015 - add CrIS full spectral resolution (FSR) coefficient files (under hi-res IR instruments).
• 15/01/2015 - add Meteor-M 2 MTVZA-GY coefficient file (under MW instruments).
• 05/12/2014 - add MSG-4 SEVIRI coefficient files (under VIS/IR instruments and IR instruments).
• 04/12/2014 - add link to script which can download all or any required coefficient files
• 02/09/2014 - updated ATSR/AATSR v9 predictor coefficient files (under VIS/IR instruments).
• 18/08/2014 - add NOAA 5-14 AVHRR v9 predictor coefficients (under VIS/IR instruments) and AATSR coefficients with shifted 12um channel (under VIS/IR instruments and IR instruments).
• 25/07/2014 - further correction to GMI Mietable file and addition of Windsat Mietable (under MW instruments).
• 18/07/2014 - added missing 1.6 micron channel to the NOAA-19 AVHRR VIS/IR v9 predictor coefficient file (under VIS/IR instruments).
• 03/07/2014 - correction to GMI Mietable file (under MW instruments).
• 02/07/2014 - start adding information on spectral response functions/pass-bands and comparisons against LBL simulations.
• 17/06/2014 - added FY3-C MWTS2, MWHS2 and MWRI coefficients (under MW instruments).
• 12/06/2014 - added EOS-1 ASTER coefficients (under IR and VIS/NIR/IR).
• 12/06/2014 - added v9 predictor (all trace gas) CrIS coefficients (under hi-res IR instruments).
• 12/06/2014 - updated AHI and FCI v7 predictor coefficients (under IR instruments).
• 12/06/2014 - updated ABI, AHI, FCI, MODIS, MODIS-shifted, OLI, SLSTR and VIIRS v9 predictor coefficients (under VIS/NIR/IR instruments).
• 07/05/2014 - begin keeping log of coefficient file histories. Where files have changed their entries in this log are linked from the "Date of file creation" in the tables below.
• 07/05/2014 - correction to NOAA-18/19 MHS coefficients (under MW instruments): the channel central wavenumbers and band corrections were mistakenly taken from the AMSU-B files.
• 27/02/2014 - updated GPM GMI coefficients with revised channel specification (under MW instruments).
• 21/02/2014 - added information about coefficient regression limits.
• 19/02/2014 - updated v9 predictor (all trace gas) coefficients for AIRS, IASI and IASI-NG based on LBLRTM v12.2 (under hires instruments).
• 13/02/2014 - added shifted AMSU-A coefficients (under MW instruments).
• 24/01/2014 - added GPM GMI coefficients (under MW instruments).
• 20/11/2013 - added MTG-FCI coefficients (under IR and VIS/NIR/IR).
• 15/11/2013 - added coefficients for Nimbus 4 IRIS (under hires), Landsat 8 OLI (under VIS/NIR/IR) and Nimbus 7 SMMR (under MW).
• 15/10/2013 - added new coefficients for IASI-NG, experimental coefficients for MTG-IRS, and v8 predictor coefficients with variable CO2 for AIRS, CrIS and IASI.
• 15/10/2013 - added notes on coefficient conversion and channel subset extraction.
• 07/10/2013 - added aerosol coefficients for HIRS and MODIS "shifted" rtcoef files (under IR instruments).
• 03/10/2013 - correction to Windsat coefficient file (under MW instruments): the sensor ID was incorrectly specified as "mw" instead of "po".
• 10/09/2013 - updated Mie table files for MW instruments. See the notes below for a description of the changes.
• 10/09/2013 - added coefficient file for Landsat 8 TIRS in IR instruments.
• 01/08/2013 - the 101L v7 and v9 predictor hi-res sounder files including NLTE coefficients uploaded previously were incorrect and have now been updated.
• 19/06/2013 - NLTE coefficients added to the hi-res sounder files.

If you read coefficients based on the platform and instrument IDs you may need the most recent version of rttov_const.F90 which contains an up to date list of all supported IDs. Place this in src/main/ and recompile. This is not required if you read coefficients by passing the filename to rttov_read_coefs which is the recommended method.

• Predictors - the predictor set determines the available optional trace gases for simulations and whether or not the coefficients support solar calculations and PC calculations. Note that v7 predictor files for IR instruments may be preferable to the solar v9 predictor files for the same instruments when only simulating IR channels (no solar).
• Trace gases - water vapour is mandatory for all simulations. The more additional trace gases supported by the coefficients the slower the simulations, so if speed is a factor and extra gases are not required choose a coefficient file with fewer gases (this applies to hyperspectral sounders).
• Levels - the majority of optical depth coefficient files are on 54 levels. Only hyperspectral sounders have coefficients on 101 levels. More levels give more accurate simulations at a cost in execution speed.
• Planck-weighting - the accuracy of simulations for very broad channels (e.g. SEVIRI channel 4 at 3.9 microns) is poor with significant biases noted (~1-2K). To mitigate this, the line-by-line transmittances in the coefficient generation are weighted with the Planck function across the instrument channel and the coefficients are computed for these Planck-weighted transmittances resulting in much reduced biases. Whether coefficients are Planck-weighted or not for a channel can be determined by examining the PLANCK_WEIGHTED section in the coefficient file (if it is not present there are no Planck-weighted channels). The tables below indicate if coefficient files contain any Planck-weighted channels.
• NLTE - the non-local thermodynamic equilibrium correction is only applicable to hi-res IR sounders. Note that the NLTE correction is a "simple" bias correction applied to the standard LTE RTTOV radiances and as such is entirely independent of solar calculations in RTTOV (see user guide).
• PC - Principal Components calculations are only applicable to hi-res IR sounders and can only be used with v9 predictor coefficient files.
• IR cloud/aerosol coefs - the cloud and aerosol coefficient files must be used in conjunction with optical depth coefficient files ("rtcoef_*") containing coefficients for the same set of channels. Subsets of channels can be extracted from optical depth and cloud/aerosol files using the rttov_conv_coef.exe executable. The cloud and aerosol coefficients depend only on the channel central wavenumbers. They are independent of the predictor version of the rtcoef_* file so the same cloud/aerosol files may be used with v7, v8 and v9 predictor-based rtcoef_* files for a given instrument.
• Solar simulations - solar simulations require coefficient files based on v9 predictors. Aerosol and cloud parameter coefficient files are not available for solar-compatible visible/IR optical depth coefficient files except for the hi-res IR sounders.
• Channel numbering - for those instruments with both v7 predictor IR-only files and v9 predictor VIS/NIR/IR files, the RTTOV channel numbering is often different for the IR channels with the two files (RTTOV channel numbers always start at one). Consult the second table on this page, the user guide or the coefficient file headers for information on the channel numbering.
• RTTOV v10 compatiblity - RTTOV v11 can read all RTTOV v10 coefficient files except for the PC coefficients. All RTTOV v11 coefficients can be read by RTTOV v10 with the following exceptions:
  visible/IR solar-compatible coefs, aerosol coefs, PC coefs. There are notes below indicating which files are v10-compatible.
• Coefficient directory structure - the notes below indicate where each type of coefficient file should be placed within the rtcoef_rttov11/ directory to run correctly with the RTTOV v11 test suite. Coefficient files may be stored in any location for your own applications.
• Coefficient file histories - a change log is now being kept of changes to coefficient files. Where files have changed their entries in this log are linked from the "Date of file creation" in the tables below.
• SSU PMC shift coefficient files - new coefficients are available for SSU which allow for variable CO2 cell pressure in the instrument: these are labelled "pmcshift".
• "Shifted" coefficient files - coefficients have been produced for AATSR, AMSU-A, HIRS and MODIS with modified spectral responses in some channels. These files are labelled with the keyword "shifted". The changes are empirically determined small shifts in the central wavenumber of some of the channels. The aim of these coefficient files is to address observed biases in the affected channels, but note that the shifted files may not necessarily result in improved simulations compared to the non-shifted files. The shifts are described in the headers of these coefficient files.

A small number of instrument IDs and names have changed since v10. Instruments now only share an ID/name where they have the same channels. The following instruments are affected:

Note for RTTOV v10 users: The affected optical depth coefficient files are compatible with RTTOV v10 if they are read via the filename (the recommended method). Mietable filenames are constructed using the instrument ID and so RTTOV v10 users wishing to make use of the AMSR-E and AMSR2 Mietable files on this page should use this version of rttov_const.F90 which contains the modified instrument names and IDs. This copy of the file should also be used if coefficient files are read into RTTOV v10 via the instrument triplet.

For MW and non-hi-res IR instruments the ASCII coefficient files can usually be used without any problem. That said, the following notes apply equally well to coefficient files for all instruments. The ASCII hi-res IR sounder coefficient files are typically very large and so HDF5 is becoming the preferred format for distribution of these files. It may be necessary or convenient to convert a given file to a different format or to extract coefficients for a subset of channels to create a smaller file. For example, the test scripts currently expect the ASCII versions of the v7 and v9 predictor AIRS and IASI files. Also, some users may prefer to use a binary unformatted or HDF5 version of a coefficient file as these are read much faster than ASCII versions.

Converting between file formats and extracting subsets of channels can be achieved using the rttov_conv_coef.exe executable which is found in the bin/ directory of your RTTOV build and is described in Annex A of the user guide. Some examples of usage are given below. Reading HDF5 coefficient files requires RTTOV to have been compiled against the HDF5 library: see the user guide for details on how to do this.

The simplest usage is to convert the format of a file. Note that you do not generally need to specify the input file format: RTTOV automatically determines the file format. For example, to create an ASCII version of an AIRS HDF5 file use the following:

$ rttov_conv_coef.exe --format-out formatted --coef-in rtcoef_eos_2_airs.H5 --coef-out rtcoef_eos_2_airs.dat

If you are running simulations for a limited subset of channels you can extract just these channels to a separate file which will naturally be much smaller and will be read in more quickly. For example, to extract channels 10, 25 and 37 from an HDF5 AIRS coefficient file use the following:

$ rttov_conv_coef.exe --format-out hdf5 --coef-in rtcoef_eos_2_airs.H5 --coef-out rtcoef_eos_2_airs_subset.H5 --channels 10 25 37

If you have a text file (say, chanlist.txt) containing a white-space-separated list of channel numbers to extract you can do the following:

$ CHANLIST=$(cat chanlist.txt)
$ rttov_conv_coef.exe --format-out hdf5 --coef-in rtcoef_eos_2_airs.H5 --coef-out rtcoef_eos_2_airs_subset.H5 --channels $CHANLIST

When using cloud and aerosol coefficient files they must contain coefficients for the same channel set as the optical depth coefficient file. If you wish to extract subsets of channels or carry out file format conversions for aerosol and/or cloud coefficients then supply the corresponding aerosol and/or cloud files as input files when using rttov_conv_coef.exe as described above and supply appropriate output filenames. All input files must be of the same format. For example:

$ rttov_conv_coef.exe --format-out formatted --coef-in rtcoef_eos_2_airs.H5 --coef-out rtcoef_eos_2_airs.dat --scaer-in scaercoef_eos_2_airs.H5 --scaer-out scaercoef_eos_2_airs.dat

The same applies to PC coefficient files, but note that in this case any channel list supplied MUST correspond to the list of predictor channels you will use with PC-RTTOV: see the user guide for more details including how to obtain these predictor channel lists.

If you read in a subset of channels from a coefficient file using the rttov_read_coefs subroutine with the channels argument, or you read in channels from a coefficient file which has been created by extracting a subset of channels from another coefficient file (as described above), then the N channels you read in will be denoted by the numbers 1, 2, ..., N in the chanprof array, and not by the original channel numbers. This also applies to the reconstructed channel list for PC-RTTOV if you supply the channels_rec argument to rttov_read_coefs: the list of reconstructed channels you pass into rttov_direct/tl/ad/k will contain indexes into this list, not the original channel numbers.

When extracting a subset of channels the channel list should be monotonically increasing in channel number. It is possible to supply channels out of order in some cases which usually results in a coefficient file with re-ordered channels, but this is not supported (and hence not recommended) usage and in particular it should not be applied to hires IR sounder files.

• No Planck-weighted channels

• All ASCII optical depth coef files may be used with RTTOV v10, but new functionality such as NLTE is not available in v10
• Cloud coef files are v10-compatible (they are the same as the v10 files)
• Aerosol coef files and PC coef files cannot be read by RTTOV v10

• All files are linked in the table below
• Due to the large size of the hi-res sounder files HDF5 is becoming the preferred format for them. New files are being made available in HDF5 format only while some of the older files are available in both ASCII and HDF5 formats. If you require an ASCII version of an HDF5-only file please contact the NWP SAF Helpdesk and the ASCII version will be uploaded. See above for notes on converting between coefficient file formats and extracting subsets of channels from coefficient files.
• HDF5 files were created using the HDF5 compression so your HDF5 library must have been compiled against zlib to read these files: this usually happens automatically when building HDF5.
• Currently the test scripts expect the HDF5 versions of the v7 and v9 predictor AIRS, IASI files and the associated aerosol, cloud and PC files.
• The same cloud and aerosol coefficient files are used with v7, v8 and v9 predictor optical depth coefficient files.
• Extract to folders as follows:
• v7 predictor 54L rtcoef files - extract to rtcoef_rttov11/rttov7pred54L/
• v7 predictor 101L rtcoef files - extract to rtcoef_rttov11/rttov7pred101L/
• v8 predictor 101L rtcoef files - extract to rtcoef_rttov11/rttov8pred101L/
• v9 predictor 101L rtcoef files - extract to rtcoef_rttov11/rttov9pred101L/
• All cloud/aerosol files - extract to rtcoef_rttov11/cldaer/
• All PC files - extract to rtcoef_rttov11/pc/

• New principal components coefficients use different predictor channel sets to previous versions of the files. You can obtain the appropriate predictor channel set in your own code using the rttov_get_pc_predictindex subroutine as demonstrated in src/test/example_pc_fwd.F90.
• The older sea-only coefficient files must only be used over sea surfaces with calcemis(:) set to true (this is not enforced by RTTOV v11.3).
• The new all-surface "landsea" PC coefficients can be used for all surface types: it is recommended to set calcemis(:) to true over sea surfaces and to use the IR emissivity atlas for land and sea-ice surfaces, but this is not strictly mandatory.
• These latter global PC coefficients can only be used over land and sea-ice surfaces with RTTOV v11.3 (such simulations will fail with v11.1 and v11.2).

The Metop-B (i.e. metop_1) IASI optical depth coefficient file is identical to the Metop-A (metop_2) coefficient file except that the satellite ID is 1 (for Metop-B) instead of 2 (for Metop-A). If you read the coefficients by filename you can use the same file for either instrument. However in the rare case that distinct files are required an ASCII Metop-A optical depth coefficient file can be used to generate a Metop-B file using the Perl script make_metopb_iasi.pl as follows:

$ ./make_metopb_iasi.pl < rtcoef_metop_2_iasi.dat

where rtcoef_metop_2_iasi.dat is any Metop-A ASCII IASI coefficient file. This creates a new file rtcoef_metop_1_iasi.dat in the current directory.
The IASI cloud/aerosol scattering and PC coefficient files are identical for Metop-A and Metop-B.

Experimental MTG-IRS coefficients have been generated using transmittances from simulated IASI spectra and a Hamming apodisation function.

• 54 levels (except SSU)
• Not solar compatible
• Not NLTE compatible
• Not PC compatible

• The new SSU PMC shift files are not v10-compatible
• All other rtcoef files are v10-compatible
• All cloud coef files are v10-compatible (they are the same as the v10 files)
• Aerosol coef files are not v10-compatible
• Note that the SLSTR and FY2-2 VISSR instrument names and IDs and the GMS imager instrument ID have changed since v10

• 54L v7 predictor files for all IR sensors - extract to rtcoef_rttov11/rttov7pred54L/
• 54L v8 predictor files - extract to rtcoef_rttov11/rttov8pred54L/
• 51L v8 predictor SSU files - extract to rtcoef_rttov11/rttov8pred51L/
• Aerosol scattering coefficient files for all sensors - extract to rtcoef_rttov11/cldaer/
• Cloud scattering coefficient files for all sensors - extract to rtcoef_rttov11/cldaer/
• Spectral response functions

* The ERS-1 ATSR coefficient file contains coefficients for 6 channels: 1-3 are the standard channels (12, 11, 3.7 microns respectively) and 4-6 are additional coefficients for the 12 micron channel using spectral responses valid at different sensor temperatures. The corresponding aerosol coefficients have been generated using this coefficient file and as such contain data for the 6 channels in the rtcoef file. However the cloud coefficient file only contains parameters for the 3 standard channels (1-3, with 1 being the 12 micron channel). Therefore if you wish to use the cloudy coefficients for ERS-1 ATSR you should first extract channels 1-3 from the rtcoef file to a separate file using the rttov_conv_coef.exe executable.

• 54 levels
• v9 predictors
• Solar compatible
• Not NLTE compatible
• Not PC compatible
• No associated aerosol/cloud coefficient files
• Note that you can run IR-only simulations using these files, but you may find the v7 predictor files above give better results for IR channels.
• Channel numbering for IR channels may differ to the v7 predictor files above: check the coefficient file headers, the user guide or the second table on this page.

• These files are not v10-compatible

• v9 predictor solar files VIS/NIR/IR instruments - extract to rtcoef_rttov11/rttov9pred54L/
• Spectral response functions

• Based on Liebe 89/92 LbL model
• All on 54 levels except for the Zeeman files
• v7 predictors
• No Planck-weighted channels
• No optional trace gases
• Cloud liquid water is an optional input
• Not solar compatible
• Not NLTE compatible
• Not PC compatible

• All rtcoef files are v10-compatible
• All mietable files are v10-compatible
• The only caveat is that the AMSR-E instrument name and the AMSR2 instrument ID and name have changed since v10 (see note at the top of this page)

• Files for all MW sensors - extract to rtcoef_rttov11/rttov7pred54L/
• Mietables are linked in the table below - extract to rtcoef_rttov11/mietable/
• Pass-band data
• Comparisons against LBL

The original RTTOV-SCATT Mie coefficients produced unrealistically high amounts of scattering from snow hydrometeors at 30-50 GHz and insufficient scattering at 150-183 GHz. The new coefficients address this problem by representing snow hydrometeors as three-dimensional snowflakes rather than Mie spheres. While it is possible to improve Mie sphere results by tuning the snow particle density, it is difficult to improve results at all frequencies simultaneously. The new snow hydrometeor optical properties are based on the "sector snowflake" from the Liu (2008) database of discrete dipole computations for nonspherical ice particles. The new particle shape was chosen because it produces the best fit between observations and ECMWF simulations across frequencies from 10 to 183 GHz (Geer and Baordo, 2014).

• Liu, G. (2008). A database of microwave single-scattering properties for nonspherical ice particles. Bulletin of the American Meteorological Society, 89(10), 1563-1570.
• Geer, A.J. and F. Baordo (2014). Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies. Atmos. Meas. Tech., 7, 1839-1860, doi:10.5194/amt-7-1839-2014

* ICI coefficients are preliminary: channel specifications may change. Work is planned to validate the spectroscopic data used at frequencies above 200GHz.

** FASTEM and TELSEM have not been trained for frequencies above 200GHz and so should be used with caution for such channels: this applies to most ICI channels and MWS channel 24.

RTTOV coefficients are trained using a set of diverse profiles which cover a wide range of values for each atmospheric variable. The fast optical depth calculations can be expected to be accurate for input profiles which lie within the profile "envelopes" defined by the minimum and maximum values for each profile variable.

By default RTTOV checks the input profile against a set of profile regression limits: it can either warn if the regression limits are exceeded or clip the values to the limits where the limits are exceeded (if the apply_reg_limits option is set to TRUE). For some time it has been the practice in RTTOV to set the regression limits to +/-10% of the profile envelope for temperature and +/-20% of the profile envelope for each gas. For highly variable gases (such as water vapour) this may be reasonable, but for less variable gases (such as CO2) the limits should probably be less permissive. The aim is to address this for the next version of RTTOV.

The tables below show the current regression limits defined in the RTTOV coefficient files. This information is contained within each coefficient file.

• 54-level regression limits
• 101-level regression limits
• 51-level regression limits (SSU only)