Laboratory Measurements of Methane Bands Applicable to Remote Sensing of the Jovian Atmosphere.

K. S. Sihra, J. J. Remedios, S. B. Calcutt, F. W. Taylor (University of Oxford)

Infrared spectroscopy has proved to be a powerful tool for obtaining information to understand the atmosphere of planets . The Near Infrared Mapping spectrometer (NIMS) on Galileo is being used to measure chemical composition, cloud structure and to resolve atmospheric dynamics. The 1-4 tex2html_wrap_inline13 m interval is dominated by methane and ammonia absorption, which are minor constituents in the Jovian atmosphere.

New laboratory measurements of the transmittance functions of methane have been made in the 1.05-5.56 tex2html_wrap_inline13 m region, at a resolution of 0.2 tex2html_wrap_inline17 , in support of NIMS analysis. These spectra were recorded using a Bruker high resolution Fourier transform spectrometer at the Rutherford Appleton Laboratory. A short path, multiple-pass absorption cell, capable of pathlengths up to 20 metres, was employed so the spectra of methane could be recorded for temperatures as low as 100K and pressures up to 5 bar. The experimental resources used are described, the quality of measured spectra is assessed and the implications for NIMS atmospheric measurements are investigated.