Vous êtes ici : Version française > Parcours du doctorant > Formation

Colloque / Séminaire

Séminaire CETHIL - Absorption shape issues in atmospheric radiative transfer and remote sensing

Le 14 novembre 2019

Salle 2.20, Bât. Carnot, INSA-Lyon

Langue / language: the presentation will be in French (slides in English)

Présenté par : Jean-Michel Hartmann, Laboratoire de Météorologie Dynamique/CNRS, Ecole polytechnique, Palaiseau, France

Jean-Michel Hartmann, Laboratoire de Météorologie Dynamique/CNRS, Ecole polytechnique, Palaiseau, France

Résumé au format pdf

A review of the effects of intermolecular collisions (i.e. of pressure) on the shape of gas phase molecular spectra as they manifest in atmospheres and laboratory experiments will be presented. This will be largely done on the basis of the content of Ref. [1] and it update in Ref.[2].

I will start by a brief introduction to the various observation geometry for recordings of atmospheric absorption and emission spectra and examples of the different types of features that can appear in these spectra. I will then discuss these structures one by one. This will be done starting from spectrally isolated lines, before considering clusters of tightly-spaced and overlapping absorption transitions affected by collisional line-mixing, the far wings of lines and bands and the associated atmospheric transparency windows, and collision-induced absorption processes (e.g.figure below). Illustrative comparisons between laboratory measurements and available models will be first presented in order to point out the main characteristics of the mechanisms involved and their spectral manifestations. The
consequences for radiative transfer in planetary atmospheres and remote sensing will then be discussed. Example will be given of the influence of proper/improper modeling of collisional effects on retrievals of volume mixing ratios, temperature, or pressure from atmospheric spectra. Finally, some remaining problems will be discussed, in order to open perspectives for future researches.

Transmission spectra recorded in solar occultation mode by the satellite-borne Atmospheric Chemistry Experiment around the 4.3 μm CO2 band looking down to various tangent heights h. The increase, with decreasing h, of the absorptions by the wings of the CO2 lines wings and, on the high frequency side, by the N2 collision-induced
band, is obvious.

[1] J.-M. Hartmann, C. Boulet, D. Robert. Collisional effects on molecular spectra. Laboratory experiments and models, consequences for applications. Elsevier, Amsterdam (2008)
[2] J.-M. Hartmann, H. Tran, R. Armante, C. Boulet, A. Campargue, F. Forget, L. Gianfrani, I. Gordon, S. Guerlet, M. Gustafsson, J. Hodges, S. Kassi, D. Lisak, F. Thibault, G. Toon. Recent advances in collisional effects on spectra of molecular gases and their practical consequences. Journal of Quantitative Spectroscocpy and Radiative Transfer 213, 178-227 (2018).