QUASI-RANDOM NARROW-BAND MODEL FITS TO NEAR-INFRARED LOW-TEMPERATURE LABORATORY METHANE SPECTRA AND DERIVED EXPONENTIAL SUM ABSORPTION-COEFFICIENTS

Near-infrared 10-cm-1 resolution spectra of methane obtained at various temperatures, pressures, and abundances are fit to a quasi-random narrow-band model. Exponential-sum absorption coefficients for three temperatures (112 K, 188 K, and 295 K), and 20 pressures from 0.000 1 to 5.6 bars, applicable to the cold environments of the major planets, are then derived from the band model for the 230 wavelengths measured from 1.6 to 2.5 mum. Root-mean-square deviations between the laboratory and the exponential-sum synthetic transmissions are reported for the best fitting 50 wavelengths. Deviations relevant to broadband, 1% spectral resolution observations such as planned to be acquired by Galileo/Near Infrared Mapping Spectrometer (NIMS) and Cassini/Visual and Infrared Mapping Spectrometer are also presented. The validity of exponential-sum coefficients derived from broadband (10 cm - 1) transmission data is demonstrated via direct comparison with line-by-line calculations. The complete atlas of coefficients is available from the Planetary Data System-Planetary Atmospheres Discipline Node.