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Analyse des spectres infrarouges thermiques émis par l'atmosphère de Titan enregistrés par l'instrument CIRS à bord de la sonde Cassini

Abstract : This work is focused on the analysis of thermal infrared spectra of Titan's atmosphere acquired by the Cassini Composite Infrared Spectrometer (CIRS) instrument. The objective is the retrieval of the vertical distributions of atmospheric temperature and abundances of trace constituents in the 100-500 km range at several latitudes in order to infer their latitudinal variations. The CIRS instrument is a Fourier transform infrared spectrometer recording spectra in the 10-1400 cm-1 spectral range, which exhibits numerous spectral signatures from the rovibrationals bands of CH4, C2H2, C2H4, C2H6, CH3C2H, C3H8, C4H2, C6H6, HCN, HC3N and CO2. The intensities of these bands depend on both the temperature and the abundances of the molecules. It is then necessary to retrieve the vertical temperature profile prior to the abundance vertical profile. We deduce the thermal profile by using the v4 methane band, centered at 1305 cm-1. The methane abundance has been measured by the GCMS instrument aboard the Huygens probe. By using this abundance and by modeling the observed spectra, we are able to retrieve the temperature at a given latitude. For this purpose, we use an inversion algorithm that solves the radiative transfer equation using simultaneously nadir and limb spectra, each probing a different altitude. This work was done for five latitudes: 55°S, 13°S, 56°S, 82°N and 83°N and is described in part II of this manuscript. The inverted vertical temperature profiles are then used to retrieve, at the same latitudes, the vertical mixing ratio profiles of the above-mentioned molecules, which mainly emit in the spectral range 600-1400 cm-1. We use an inversion algorithm combining both nadir and limb spectra to retrieve the vertical abundance profiles. This work and the results are detailed in Part III. The last part of the work presented here is dedicated to the studies of the 13C/12C and 15N/14N isotopic ratios in HCN, and the D/H ratio measured in C2H2. Results obtained at several latitudes and their implications concerning the Titan atmosphere are described in Part IV.
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Contributor : Sandrine Vinatier <>
Submitted on : Monday, March 15, 2010 - 1:32:57 AM
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  • HAL Id : tel-00463734, version 1

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Sandrine Vinatier. Analyse des spectres infrarouges thermiques émis par l'atmosphère de Titan enregistrés par l'instrument CIRS à bord de la sonde Cassini. Astrophysique [astro-ph]. Université Paris-Diderot - Paris VII, 2007. Français. ⟨tel-00463734⟩

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