SPEED-DEPENDENT BROADENING AND LINE-MIXING IN CH4 PERTURBED BY AIR NEAR 1.64 _m FOR THE FRENCH/GERMAN CLIMATE MISSION MERLIN

Delahaye, Thibault

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Title

SPEED-DEPENDENT BROADENING AND LINE-MIXING IN CH4 PERTURBED BY AIR NEAR 1.64 _m FOR THE FRENCH/GERMAN CLIMATE MISSION MERLIN

Author(s)

Delahaye, Thibault

Contributor(s)

• Hodges, Joseph
• Maxwell, Stephen E
• Reed, Zachary
• Tran, Thi Ngoc Ha

Issue Date

25-Jun-15

Keyword(s)

Atmospheric science

Abstract

Climate change is one of the greatest challenges presently facing mankind, and methane is one of the most powerful anthropogenic greenhouse gases. For a better understanding of future climate trends, a satellite dedicated to the measurements of atmospheric methane is under joint development by the French and German space research centers (CNES and DLR). The so-called MERLIN mission (Methane Remote Sensing Lidar Mission, 2019) aims at providing global information on atmospheric methane concentration with a relative uncertainty less than 2% and with a spatial resolution of 50 kmfootnote{C. Kiemle, M. Quatrevalet, G. Ehret et al., Atmos. Meas. Tech. 4 (2011)}. Such spectroscopic monitoring of gases in the atmosphere of the Earth, requires a precise description of absorption lines shapes that goes beyond the usual Voigt profile (VP). In the case of methane, the differences between the measured profiles and those given by the VP can be very important footnote{H. Tran, J.-M. Hartmann, G. Toon et al., Journal of Quant. Spectrosc. Radia. Trans. 111 (2010)}, making the VP completely incompatible with the reliable detection of sources and sinks from space. In this work, we present the first results on the modeling of methane lines broadened by air in the 1.64 $mu$m region and the associated spectroscopic parameters, taking into account various collisional effects between molecules that are neglected by the VP: collisional interference between the lines (line-mixing), collision-induced velocity changes (Dicke narrowing effect) and speed dependence of the collisional broadening and shifting. These results were obtained by simultaneously fitting the model parameters to high sensitivity and high-resolution cavity ring-down spectroscopy (CRDS) spectra recorded at the National Institute of Standards and Technology (NIST) over a wide pressure range (5 to 100 kPa). These spectroscopic data and the associated model to calculate the spectrum absorption coefficient will be then used to analyze ground-based atmospheric spectra at the TCCON facility in Park Falls, Wisconsin.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

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