Line profile study by diode laser spectroscopy in the CH4ν2 + ν4 band

We present a complete study on four methane lines for two atmospheric micro-windows (in the ν₂ + ν₄ absorption band) used for the determination of atmospheric methane concentrations with ground-based Fourier transform spectrometers. Thanks to our tunable diode laser (TDL) spectrometer with active wavenumber control and step-by-step recording mode we have improved the accuracy on intensity, broadening, narrowing, and pressure shift parameters. To make our results directly useable in atmospheric models which usually assume a Voigt line shape, we have parameterised an effective-broadening parameter γ_Voigt (P) for each line and each gas mixture (CH₄-N₂ and CH₄-O₂). When this parameterisation is used to fit a “true” line profile, the same concentration as with more sophisticated models is retrieved using a consistent set of spectroscopic parameters in both approaches.