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Announcement of new version of RTTOV fast RT model - RTTOV-8

The development of the RTTOV fast radiative transfer model, which is part of the EUMETSAT sponsored NWP-SAF activities, has continued since the release of RTTOV-7 in March 2002. Over the last 2 years more developments have been made leading to the release of RTTOV-8 in Nov 2004.

New features of RTTOV-8 include:

  • Code completely rewritten in Fortran-90 using structures
  • Option for using different optical depth predictors from RTTOV-7 for water vapour and ozone and CO2 is now an optional variable gas.
  • Coefficient files available soon based on most recent spectroscopic databases
  • Improved microwave sea surface emissivity model - FASTEM-3
  • Capability to simulate polarimetric radiometers eg WINDSAT
  • Capability to simulate IASI and CrIS (coeff files not available yet)
  • Improved computation of multilayer cloudy radiances in RTTOVCLD
  • Computation of precipitation affected microwave radiances using RTTOVSCATT wrapper code similar to RTTOVCLD (note currently this only works for SSM/I)
  • There are additional routines which allow users to continue to use their RTTOV-7 interface in their code but to call RTTOV-8 code to be called inside to benefit from some of the new options.

The users guide and other documentation are included with the code but can also be accessed from the NWP-SAF web site at:

The model is available in 2 formats:

  • unix compressed tar file transferred via ftp from ECMWF.
  • unix compressed tar file and expanded files on CDROM.

Do I need to bother to upgrade my version of RTTOV to RTTOV-8? If you want any of the following, the answer is yes:

  • Cleaner Fortran 90 code for integration in your applications
  • Simulations for IASI or WINDSAT
  • Better IR cloudy radiance simulations
  • Improved microwave window channel radiances over the ocean
  • Possibilities to upgrade to newer spectroscopy and hence better accuracy with new coeff files available soon
  • Ability to change number of levels with same executable (i.e. driven by coeff file)
  • Slightly faster execution times, much faster for SSM/I, SSMIS or TMI
  • Much reduced use of memory for AIRS simulations
  • Ability to run scattering calculations for microwave radiances to simulate precipitation effects

We will continue to maintain the RTTOV-7 version and issue bug fixes if required via the RTTOV-7 web page.

To obtain a copy of the new RTTOV-8 model please complete the form on-line at: and you will then be sent a licence agreement to sign and fax back. On receipt of this fax ECMWF will give you access to the code which is provided to all non commercial users free of charge.

Roger Saunders