Publication Date:
2019
Description:
Abstract
The ability to precisely model methane absorption in the R(6) manifold of the 2ν3 band at atmospheric pressure and temperature conditions is a key technical requirement of the German‐French, Methane Remote Sensing LIDAR (MERLIN) space mission. To this end, twenty‐seven high‐resolution and high signal‐to‐noise ratio absorption spectra of air‐broadened 12CH4 were recorded using a variable‐temperature frequency‐stabilized cavity ring‐down spectroscopy apparatus. The measurement conditions corresponded to sample temperature, pressure and methane molar fraction values spanning 220 K ‐ 290 K, 4 kPa ‐ 110 kPa and 4 μmol mol‐1‐7 μmol mol‐1, respectively. The measured spectra were fit using the sum of isolated Hartmann‐Tran profiles with the addition of line‐mixing. For each line within the manifold, all spectroscopic parameters at room temperature were fixed to our previously obtained values [Delahaye et al., J Geophys Res Atmos 2016:3045‐20] and only the temperature dependences of the model parameters were adjusted. The results show that the fitted model agrees with the measured methane absorption to better than 0.3% for the entire R(6) manifold spectral region and to within 0.1% at the on‐line position of the MERLIN mission for all considered pressure and temperature conditions. A first comparison with ground‐based atmospheric measurement was also made showing significant improvement with respect to existing spectroscopic modeling of methane absorption.
Print ISSN:
2169-897X
Electronic ISSN:
2169-8996
Topics:
Geosciences
,
Physics
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