What is RTTOV?
RTTOV stands for Radiative Transfer for TOVS and is a very fast
radiative transfer model for nadir-viewing passive visible, infrared and
microwave satellite radiometers, spectrometers and interferometers.
It is a FORTRAN-90 code for simulating satellite radiances, designed
to be incorporated within users' applications. For all the satellite
sensors supported (see tables below)
then, given an atmospheric profile of temperature, water vapour
and optionally other trace gases (for example ozone and
carbon dioxide) together with satellite and solar zenith angles and surface
temperature, pressure and optionally surface emissivity and reflectance, RTTOV
will compute the top of atmosphere radiances in each of the channels
of the sensor being simulated. Users can specify the channels
to be simulated. Mathematically, in vector notation, given a
state vector, x, which describes the atmospheric/surface state
as a profile and surface variables and a radiance vector, y,
for all the channels required to be simulated then:
y = H(x)
where H is the radiative transfer model, i.e. RTTOV (also referred to as the observation operator in data assimilation parlance). This is known as the 'direct' or 'forward' model.
In addition RTTOV also computes the Jacobian matrix H which gives the change in radiance δy for a change in any element of the state vector δx assuming a linear relationship about a given atmospheric state x0:
δy = H(x0)δx
The elements of H contain the partial
derivatives 
where the subscript i refers to channel number
and j to position in state vector. The Jacobian
gives the top of atmosphere radiance change for each channel from
each level in the profile given a unit perturbation at any level
of the profile vectors or in any of the surface/cloud parameters.
It shows clearly, for a given profile, which levels in the atmosphere
are most sensitive to changes in temperature and variable gas concentrations
for each channel. RTTOV_K (and its associated subroutines ending
in K) compute the H(x0) matrix
for each input profile.
It is not always necessary to store and access the full Jacobian matrix H and so the RTTOV package also has routines to only output the tangent linear values δy, i.e. the change in top of atmosphere radiances, for a given change in atmospheric profile, δx, about an initial atmospheric state x0. The tangent linear routines all have TL as an ending. Conversely the adjoint routines (ending in AD) compute the change in the gradient of any scalar quantity with respect to the atmospheric state, x0, given a change in the gradient of that quantity with respect to the radiances, y. These routines are normally used as part of the variational assimilation of radiances.
For users only interested in the direct or forward model for radiance simulations the TL/AD/K routines are not required.
Table 1: Platforms supported by RTTOV v11 as of September 2015.
Platforms in italics are not yet supported in the RTTOV v11 distribution but can be requested.
| Platform | RTTOV platform ID | Satellite ID range |
| NOAA (includes TIROS-N) | 1 | 1 - 19 |
| DMSP | 2 | 8 - 19 |
| Meteosat | 3 | 1 - 7 |
| GOES | 4 | 4 - 16 |
| GMS | 5 | 5 |
| FY-2 | 6 | 2 - 4 |
| TRMM | 7 | 1 |
| ERS | 8 | 1 - 2 |
| EOS | 9 | 1 - 2 |
| METOP | 10 | 1 - 2 |
| ENVISAT | 11 | 1 |
| MSG | 12 | 1 - 4 |
| FY-1 | 13 | 3 - 4 |
| ADEOS | 14 | 2 |
| MTSAT | 15 | 1 - 2 |
| CORIOLIS | 16 | 1 |
| JPSS/NPP | 17 | 0 |
| GIFTS | 18 | 1 |
| Sentinel3 | 19 | 1 |
| MeghaTropique | 20 | 1 |
| Kalpana | 21 | 1 |
| Meteor | 22 | 1 |
| FY-3 | 23 | 1 - 3 |
| COMS | 24 | 1 |
| METEOR-M | 25 | 1 |
| GOSAT | 26 | 1 |
| CALIPSO | 27 | 1 |
| Reserved | 28 | |
| GCOM-W | 29 | 1 |
| NIMBUS | 30 | 3, 4, 6, 7 |
| Himawari | 31 | 8 |
| MTG | 32 | 1 |
| Saral | 33 | 1 |
| Metop-SG | 34 | 1 |
| Landsat | 35 | 4, 5, 7, 8 |
| JASON | 36 | 2 |
| GPM | 37 | 1 |
| INSAT-1 | 38 | 1 - 4 |
| INSAT-2 | 39 | 1 - 5 |
| INSAT-3 | 40 | 1 - 5 |
| Reserved | 41 | |
| DSCOVR | 42 | 1 |
| CLARREO | 43 | 1 |
| TICFIRE | 44 | 1 |
| Reserved | 45 |
Table 2: Instruments supported by RTTOV v11 as of September 2015.
Sensors in italics are not yet supported in the RTTOV v11 distribution but can be requested.
"IR/MW-only" refers to v7/v8 predictor files; "VIS/NIR/IR" refers to v9 predictor solar-compatible files.
* Channels 19-21 are only simulated accurately with Zeeman coefficient files.
** Channels in coefficient files are in order of decreasing wavenumber.
*** Channel numbering follows instrument convention.
| Sensor | RTTOV sensor ID | Sensor chans => RTTOV chans (IR/MW-only) |
Sensor chans => RTTOV chans (VIS/NIR/IR) |
| HIRS | 0 | 1-19 => 1-19 | - |
| MSU | 1 | 1-4 => 1-4 | - |
| SSU** | 2 | 1-3 => 1-3 | - |
| AMSU-A | 3 | 1-15 => 1-15 | - |
| AMSU-B | 4 | 1-5 => 1-5 | - |
| AVHRR** | 5 | 3b-5 => 1-3 | 1-6 => 1-6 |
| SSMI | 6 | 1-7 => 1-7 | |
| VTPR1*** | 7 | 1-8 => 1-8 | - |
| Spare | 8 | ||
| TMI | 9 | 1-9 => 1-9 | - |
| SSMIS*** | 10 | 1-24 => 1-24* | - |
| AIRS | 11 | 1-2378 => 1-2378 | 1-2378 => 1-2378 |
| HSB | 12 | 1-4 => 1-4 | - |
| MODIS | 13 | (20-25, 27-36) => 1-16** | 1-36 => 1-36*** |
| ATSR | 14 | 1-3 => 1-3 | 1-7 => 1-7 |
| MHS | 15 | 1-5 => 1-5 | - |
| IASI | 16 | 1-8461 => 1-8461 | 1-8461 => 1-8461 |
| AMSR-E | 17 | 1-12 => 1-12 | - |
| GMS imager*** | 18 | 1-3 => 1-3 | - |
| ATMS | 19 | 1-22 => 1-22 | - |
| MVIRI** | 20 | 1-2 => 1-2 | - |
| SEVIRI** | 21 | 4-11 => 1-8 | 1-12 => 1-12 |
| GOES imager** | 22 | 2-5 => 1-4 | 1-5 => 1-5 |
| GOES sounder | 23 | 1-18 => 1-18 | - |
| MTSAT imager*** | 24 | 1-4 => 1-4 | 1-5 => 1-5 |
| FY2-3/4 VISSR** | 25 | 2-5 => 1-4 | 1-5 => 1-5 |
| FY1-MVISR** | 26 | 1-3 => 1-3 | - |
| CrIS CrIS-FSR (Full Spectral Resolution) |
27 | 1-1305 => 1-1305 1-2211 => 1-2211 |
- |
| Spare | 28 | ||
| VIIRS*** | 29 | 16-22 => 1-7 | 1-22 => 1-22 |
| WINDSAT | 30 | 1-16 => 1-16 | - |
| GIFTS | 31 | - | - |
| SSM-T1 | 32 | 1-7 => 1-7 | - |
| SSM-T2 | 33 | 1-5 => 1-5 | - |
| SAPHIR | 34 | 1-6 => 1-6 | - |
| MADRAS | 35 | 1-9 => 1-9 | - |
| Reserved | 36 | ||
| VHRR | 37 | 2-3 => 1-2 | 1-3 => 1-3*** |
| INSAT imager | 38 | 3-6 => 1-4 | 1-6 => 1-6 |
| INSAT sounder | 39 | 1-18 => 1-18 | 1-19 => 1-19 |
| FY3 MWTS | 40 | 1-4 => 1-4 | - |
| FY3 MWHS | 41 | 1-5 => 1-5 | - |
| FY3 IRAS | 42 | 1-20 => 1-20 | - |
| FY3 MWRI | 43 | 1-10 => 1-10 | - |
| GOES-R ABI** | 44 | 7-16 => 1-10 | 1-16 => 1-16 |
| COMS MI** | 45 | 2-5 => 1-4 | 1-5 => 1-5 |
| MSUMR | 46 | 1-3 => 1-3 | - |
| TANSO-FTS | 47 | - | - |
| Calipso IIR** | 48 | 1-3 => 1-3 | - |
| ESA MWR | 49 | 1-2 => 1-2 | - |
| Reserved | 50-53 | ||
| SCAMS | 54 | 1-5 => 1-5 | - |
| SMMR | 55 | 1-10 => 1-10 | - |
| AHI** | 56 | 7-16 => 1-10 | 1-16 => 1-16 |
| MTG IRS | 57 | 1-1738 => 1-1738 | 1-1738 => 1-1738 |
| AltiKa | 58 | 1-2 => 1-2 | - |
| IASI-NG | 59 | 1-16921 => 1-16921 | 1-16921 => 1-16921 |
| Landsat TM | 60 | 6 => 1 | - |
| MTG FCI** | 61 | 9-16 => 1-8 | 1-16 => 1-16 |
| AMSR1 | 62 | 1-16 => 1-16 | - |
| AMSR2 | 63 | 1-14 => 1-14 | - |
| FY2-2 VISSR** | 64 | 1-2 => 1-2 | - |
| SLSTR** | 65 | 7-9 => 1-3 | 1-9 => 1-9 |
| TIRS** | 66 | 10-11 => 1-2 | - |
| AMR | 67 | 1-3 => 1-3 | - |
| OLI*** | 68 | - | 1-9 => 1-9 |
| IRIS | 69 | 1-862 => 1-862 | - |
| ICI | 70 | 1-13 => 1-13 | - |
| GMI | 71 | 1-13 => 1-13 | - |
| FY3 MWTS2 | 72 | 1-13 => 1-13 | - |
| FY3 MWHS2 | 73 | 1-15 => 1-15 | - |
| ASTER** | 74 | 10-14 => 1-5 | (1-2,3N,3B,4-14) => 1-15 |
| Reserved | 75 | ||
| MTVZAGY | 76 | 1-29 => 1-29 | - |
| MetImage** | 77 | 11-20 => 1-9 | 1-20 => 1-20 |
| MWS | 78 | 1-24 => 1-24 | - |
| MWI | 79 | 1-26 => 1-26 | - |
| EPIC | 80 | - | - |
| MRIR | 81 | 2-5 => 1-4 | - |
| Reserved | 82-86 | ||
| MERSI-1 | 87 | - | - |
| MERSI-2 | 88 | - | - |