| Abstract: |
RTTOV (Radiative Transfer (model) for TOVS (TIROS Operational Sounder)) is a satellite simulator developed under the EUMETSAT-funded NWP SAF, with the Met Office, Météo-France and ECMWF all contributing to its development. It has a wide usage across the world, due to it being very fast whilst retaining high accuracy with respect to line-by-line codes. Until recently the microwave part of the code only dealt with frequencies up to 300 GHz, however, a new generation of satellite instruments such as ICI (Ice-Cloud-Imager), will have channels approaching 1 THz where the science is very different and less well-known. In readiness for their launch spectroscopic improvements to AMSUTRAN, the line-by-line code upon which RTTOV is trained, are being tested and implemented. AMSUTRAN (not just for AMSU) is a model which calculates channel averaged transmittances and can also be used as a monochromatic line-by-line code. Originally only using the radio engineering line parameters calculated by Hans Liebe's 1989 Millimeter-Wave Propagation Model (MPM), it has recently undergone significant redevelopment including the addition of more lines, updated line parameters, and a new water vapour continuum parametrisation based on the results of state-of-the-art research. The UK Met Office has performed a number of test flights with ISMAR (International SubMillimetre Airborne Radiometer) , the airborne prototype for ICI, and upward looking measurements have compared with equivalent simulations to assess the best choices for the new spectroscopy. The latest release of the HITRAN spectroscopic database is utilised and a model of the water vapour self-continuum developed from the recent first measurements of the water vapour dimer is being tested against observations in order to prepare RTTOV for this little know part of the Earth's atmospheric spectrum.
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