V. BOUDON, Institut Carnot de Bourgogne, UMR 5209 CNRS-Université de Bourgogne, 9. Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France; A. COUSTENIS, E. LELLOUCH, P. DROSSART, LESIA, Observatoire de Paris-Meudon, 5 Place Jules Jansen, F-92195 Meudon Cedex, France; A. NEGR AO, Observatorio Astronomico and Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal; C. A. GRIFFITH, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, 85721 USA.
The advent of the Cassini-Huygens mission studying Saturn's system and its largest moon Titan, has led to a renewed interest in reliable models of the absorption spectrum of methane. CH4 is the main absorber in Titan's thick atmosphere. Although the models developed in the Dijon group still do not allow sufficently reliable simulations above 5000 cm-1 to reproduce all the recent data (such as Huygens/DISR spectra, for instance), the methane coefficients in the 0--4800 cm-1 region have contributed to a better understanding of various ground- and spaced-based data : ISO high-resolution data in the 3 µm region\footnoteA. Coustenis, A. Negrao, A. Salama et al.\/ Icarus\/ 180, 176--185 (2006)., near-infrared VLT data\footnoteA. Negrao, A. Coustenis, E. Lellouch et al.\/ Planet. Space Sci.\/ 54, 1225--1246 (2006). and 2 µm VLT data of the Huygens probe landing site\footnoteA. Negrao, M. Hirtzig, A. Coustenis et al.\/ J. Geophys. Res. Planets\/ 112, E02S92 (2007).. These coefficients have also contributed to the discovery of a polar ethane cloud on Titan\footnoteC. A. Griffith, P. Penteado, P. Rannou et al.\/ Science\/ 313, 1620--1622 (2006).. Models of CH4 hot bands by the Dijon group are also of primary importance for fluorescence calculations observed at 3.3 µm with Cassini/VIMS. After a short review of these works, future prospects for line-by-line analyses of CH4 spectra for planetary applications will also be discussed and compared to other approaches, such as the so-called band models or purely experimental approaches.