37th DPS Meeting, 4-9 September 2005
Session 67 Laboratory Research
Oral, Friday, September 9, 2005, 2:00-3:30pm, Law LG19

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[67.04] Near infrared transmission of methane: revised band and k-distribution parameters.

P.G.J. Irwin (University of Oxford), L.A. Sromovsky (University of Wisconsin), E.K. Strong (University of Toronto), K. Sihra (UK National Radiological Protection Board), N. Bowles (University of Oxford), J. Remedios (University of Leicester), S.B. Calcutt (University of Oxford)

Laboratory measurements of the near infrared transmission spectra of methane by Strong et al. (1993) and Sihra (1998) have been remodelled and re-fitted with an improved band model. The methane data are recorded at a resolution of 10 cm-1, with a step of 5 cm-1 and cover a wide range of temperatures, pressures and path lengths for both self- and hydrogen broadened conditions. The revised band parameters better approximate the measured spectra and are more reliably extrapolated outside of the measurement conditions than the previous fits of Sihra (1998), which were reported by Irwin et al. (2005). Using these new band parameters, revised k-distribution tables have been fitted.

Although the near infrared line data of methane of the GEISA and HITRAN line compilations is improving all the time, the coverage of weak lines becomes insufficient at short wavelengths. Hence, these new lower resolution laboratory data, which have been measured for both long path lengths and cold temperatures provide a valuable intermediate representation of methane opacity until such time as the line databases are more complete. These data should thus be of great use in modelling the near infrared spectra of the giant planets and Titan.

We would like to acknowledge the funding of the Particle Physics and Astronomy Research Council.

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