What is RTTOV?
RTTOV stands for Radiative Transfer for TOVS and is a very fast
radiative transfer model for nadir viewing passive 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 ozone and
carbon dioxide together with satellite zenith angle and surface
temperature, pressure and optionally surface emissivity, 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.
| Platform | RTTOV platform id | Sat id range |
| NOAA* | 1 | 1 to 19 |
| DMSP | 2 | 8 to 18 |
| Meteosat | 3 | 1 to 7 |
| GOES | 4 | 4 to 16 |
| GMS | 5 | 5 |
| FY-2 | 6 | 2 to 4 |
| TRMM | 7 | 1 |
| ERS | 8 | 1 to 2 |
| EOS | 9 | 1 to 2 |
| METOP | 10 | 2 |
| ENVISAT | 11 | 1 |
| MSG | 12 | 1 to 3 |
| FY-1 | 13 | 3 to 4 |
| ADEOS | 14 | 1 to 2 |
| MTSAT | 15 | 1 to 2 |
| CORIOLIS | 16 | 1 |
| JPSS/NPP | 17 | 0 |
| GIFTS | 18 | 1 |
| Sentinel | 19 | 1 |
| MeghaTropique | 20 | 1 |
| Kalpana | 21 | 1 |
| Reserved | 22 | |
| FY-3 | 23 | 1 |
| COMS | 24 | 1 |
| METEOR-M | 25 | 1 |
| GOSAT | 26 | 1 |
| CALIPSO | 27 | 1 |
| Reserved | 28 | |
| GCOM-W | 29 | 1 |
| NIMBUS | 30 | 6 to 7 |
Table 1. Platforms supported by RTTOV v10.2 as of April 2012.
Platforms in italics are not yet supported in the RTTOV v10 distribution but can be requested.
* Includes TIROS-N
| Sensor | RTTOV sensor id | Sensor Channel # | RTTOV Channel # |
| HIRS | 0 | 1 to 19 | 1 to 19 |
| MSU | 1 | 1 to 4 | 1 to 4 |
| SSU** | 2 | 1 to 3 | 1 to 3 |
| AMSU-A | 3 | 1 to 15 | 1 to 15 |
| AMSU-B | 4 | 1 to 5 | 1 to 5 |
| AVHRR** | 5 | 3b to 5 | 1 to 3 |
| SSMI | 6 | 1 to 7 | 1 to 7 |
| VTPR1*** | 7 | 1 to 8 | 1 to 8 |
| VTPR2*** | 8 | 1 to 8 | 1 to 8 |
| TMI | 9 | 1 to 9 | 1 to 9 |
| SSMIS*** | 10 | 1 to 24* | 1 to 24* |
| AIRS | 11 | 1 to 2378 | 1 to 2378 |
| HSB | 12 | 1 to 4 | 1 to 4 |
| MODIS** | 13 | 1 to 16 | 1 to 16 |
| ATSR/SLSTR | 14 | 1 to 3/7 to 9 | 1 to 3 |
| MHS | 15 | 1 to 5 | 1 to 5 |
| IASI | 16 | 1 to 8461 | 1 to 8461 |
| AMSR-E/AMSR2 | 17 | 1 to 12/1 to 14 | 1 to 12/1 to 14 |
| Reserved | 18 | ||
| ATMS | 19 | 1 to 22 | 1 to 22 |
| MVIRI** | 20 | 1 to 2 | 1 to 2 |
| SEVIRI** | 21 | 4 to 11 | 1 to 8 |
| GOES-Imager** | 22 | 1 to 4 | 1 to 4 |
| GOES-Sounder | 23 | 1 to 18 | 1 to 18 |
| GMS/MTSAT imager*** | 24 | 1 to 3/1 to 4 | 1 to 3/1 to 4 |
| FY2-VISSR** | 25 | 1 to 2/4 | 1 to 2/4 |
| FY1-MVISR** | 26 | 1 to 3 | 1 to 3 |
| CrIS | 27 | 1 to 1305 | 1 to 1305 |
| VIIRS | 29 | 16 to 22 | 1 to 7 |
| WINDSAT | 30 | 1 to 16 | 1 to 16 |
| GIFTS | 31 | TBD | TBD |
| SSM-T1 | 32 | 1 to 7 | 1 to 7 |
| SSM-T2 | 33 | 1 to 5 | 1 to 5 |
| SAPHIR | 34 | 1 to 6 | 1 to 6 |
| MADRAS | 35 | 1 to 9 | 1 to 9 |
| Spare | 36 | ||
| Kalpana Imager** | 37 | 1 to 2 | 1 to 2 |
| Reserved | 38-39 | ||
| FY-3 MWTS | 40 | 1 to 4 | 1 to 4 |
| FY-3 MWHS | 41 | 1 to 5 | 1 to 5 |
| FY-3 IRAS | 42 | 1 to 20 | 1 to 20 |
| FY-3 MWRI | 43 | 1 to 10 | 1 to 10 |
| GOES-R ABI** | 44 | 1 to 3 | 1 to 3 |
| COMS MI** | 45 | 1 to 4 | 1 to 4 |
| MSUMR | 46 | 1 to 3 | 1 to 3 |
| Reserved | 47 | ||
| Calipso IIR | 48 | 1 to 3 | 1 to 3 |
| ESA MWR | 49 | 1 to 2 | 1 to 2 |
| Reserved | 50-53 | ||
| SCAMS | 54 | 1 to 5 | 1 to 5 |
| SMMR | 55 | 1 to 5 | 1 to 5 |
Table 2. Instruments supported by RTTOV v10.2 as of April 2012.
Sensors in italics are not yet supported in the RTTOV v10 distribution but can be requested.
* 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.