Self- and air-broadened line shapes in the 2ν3 P and R branches of 12CH4

Precise methane absorption measurements in the 1.64 μm spectral region for the MERLIN mission

“…With regard to other parameters, the direct comparison with previous studies is difficult because of differences in the line shape models considered. We noticed for example that our values of the broadening parameters were slightly lower than those of other studies [ Pine , ; Devi et al ., ]. Due to the strong overlapping within the considered R(6) transitions, the first‐order approximation is not able to fully describe line mixing, thus leading to effective line‐mixing parameters which do not satisfy the sum rule [ Hartmann et al ., ].…”

“…[] and Devi et al . []. For the first set (Set 1), four spectra of methane diluted in N 2 were measured at room temperature for pressures ranging from 126 hPa to 900 hPa using a high‐resolution FTS spectrometer [ Frankenberg et al ., ].…”

“…In the second set (Set 2), four air‐broadened, room temperature methane FTS spectra of Devi et al . [] were measured at pressures from 331 hPa to 1179 hPa. Details of the experimental setups and conditions can be found in the corresponding references.…”

“…An overview of recent measurements of the line‐shape parameters of the 2ν 3 band of 12 CH 4 can be found in Devi et al . []. The R(6) manifold was investigated by four studies, [ Frankenberg et al ., ; Lyulin et al ., ; Lyulin et al ., ; Devi et al ., ], all of which were based on Fourier transform spectroscopy (FTS).…”

“…Except for Devi et al . [], the other studies adopted the Voigt profile (VP) to represent the line shapes of isolated methane transitions. This profile is now considered as obsolete for many applications since it cannot reproduce absorption spectra to within a precision of a few percent [ Hartmann et al ., ; Ngo et al ., ; Birk and Wagner , ].…”