RTTOV Overview

Please note that resources and documentation for older versions of RTTOV can be found on the archived old site.

Introduction

Current version: v11.3, September 2015

RTTOV (Radiative Transfer for TOVS) is a very fast radiative transfer model for passive visible, infrared and microwave downward-viewing satellite radiometers, spectrometers and interferometers. It is a FORTRAN 90 code for simulating satellite radiances, designed to be incorporated within user applications.

Given an atmospheric profile of temperature, water vapour and, optionally, trace gases, aerosols and hydrometeors, together with surface parameters and a viewing geometry, RTTOV will compute the top of atmosphere radiances in each of the channels of the sensor being simulated.

In addition, RTTOV also optionally computes the Jacobian matrix which describes the change in radiance for a change in any element of the state vector assuming a linear relationship about a given atmospheric state. For a brief mathematical overview of radiative transfer modelling see this page.

The most recent version of RTTOV is v11.3, released in September 2015.

Some example applications of using RTTOV software are given on the RTTOV applications page.

Obtaining RTTOV

RTTOV is available to licensed users free of charge. To become a licensed user of RTTOV, please register with the NWP SAF (or login if you have already done so) and add RTTOV to your list of software preferences. Older versions of RTTOV are available to download to maintain compatibility with certain software but are not supported by the NWP SAF.

It is recommended (though not mandatory) to compile RTTOV against the HDF5 library (v1.8.8 or later required). This enables the use of HDF5 format coefficient files (the preferred format for hyperspectral sounders), the land surface emissivity and BRDF atlases, the Python and C++ interface to RTTOV and the RTTOV GUI.

If you do not compile against the HDF5 library you can still use the land surface emissivity and BRDF atlases and the Python/C++ interface if you compile RTTOV against the netCDF library (v3.6 or later).

In order to compile the RTTOV GUI or to call RTTOV from Python scripts you must also have F2PY (part of NumPy ) installed.

The GUI has additional requirements which are given in the GUI users’ guide.

Documentation and Resources

Instructions for compiling and running the most recent version of RTTOV may be found here. The User Guide also contains comprehensive details of the new features in RTTOV v11 and the changes from RTTOV v10. Further documentation, including the RTTOV ‘Science and validation report’ can be found on the RTTOV 11 homepage.

Resources (coefficients, atlases, etc.) compatible with RTTOV v11 can be accessed on the downloads page.

Future Plans

RTTOV v12 developments

  • Scientific changes
    • Multiple-scattering simulations for visible/near-IR channels
    • Allow SO2 as an optional trace gas
    • Updated sea surface IR emissivity model (the existing ISEM model will be retained as an option in v12 and removed in v13)
    • Update the IR land surface emissivity atlas with the new combined MODIS+ASTER (“MODAST”) dataset developed by U. Wisconsin/JPL
    • Extension of PC-RTTOV simulations to all trace gases and aerosols
    • Offer the option of mixing ratio for the input unit for cloud and aerosol in IR scattering simulations
    • Provide interface to the HT-FRTC fast PC-based RT model: this will enable simulations of unapodised/self-apodised radiances
    • Plan to investigate possible improvements to water vapour optical depth prediction in the VIS/IR outside the IASI spectral range
    • Remove old hexagonal/aggregrate and Baran 2013 ice parameterisations for IR cloudy simulations (the Baran 2014 parameterisation will remain)
    • Produce coefficient files which can account for the variation in trace gases such as CO2 over the whole satellite era
    • RTTOV GUI will be kept up to date with new RTTOV developments
  • Technical changes
    • Extend the capabilities of the Python/C++ interface (enable calls to RTTOV-SCATT and PC-RTTOV)
    • Update to the FORTRAN2003 standard
    • Land surface BRDF and IR emissivity atlases will ONLY be available in HDF5 format (no netCDF dependence in RTTOV which will simplify compilation)
    • More efficient code particularly on scalar supercomputer architectures
    • Removal of some redundant options and some changes to interface to improve consistency (all changes from v11 will be clearly documented)

Longer-term developments

  • UV simulation capability
  • Improvements to VIS/NIR/IR scattering simulations
  • Improvements to RTTOV_SCATT simulations for MW radiances affected by hydrometeors
  • Update LBL transmittance databases
  • Updates to ocean and land surface emissivity
  • Further code optimisation
  • Investigate possibility of making RTTOV available via Linux package management systems (e.g. RedHat RPM, Debian package)

Users wishing to make suggestions for new features should contact the helpdesk.