Étude des nuages de Vénus par polarimétrie avec les données de l’instrument SPICAV-IR à bord de Venus Express

Loïc Rossi 1
1 IMPEC - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : Venus is quite similar to Earth in terms of mass and radius, but it appears to be a hellish planetwith surface temperature reaching 700 K and pressions up to 92 bars. The atmosphere is mostlycomposed of carbon dioxyde and despite a slow retrograde rotating solid body, the atmosphereis in superrotation with a period of about four days and zonal winds reaching 100 m/s at cloudtop level. In visible light, the surface is always hidden by thick decks of clouds mostly madeof sulfuric acid. These clouds are very important in venusian climate as they play a key role inthe radiative balance of the planet because of their opacity and their high albedo and also in thechemical cycles of sulfur especially.In orbit since 2006, the European space agency’s probe Venus Express had the objective tostudy the atmosphere and clouds of Venus. Amongst its instruments was the SPICAV spectrometerwhich infrared channel had the ability to measure the degree of linear polarisation fromthe light scattered by the clouds. This thesis aims to study these observations acquired by SPICAVIRuntil the end of the mission in 2014.We will introduce the planet Venus with a particular focuson the cloud layers. We will then cover the principles of the polarisation of light through scatteringby cloud particles before we introduce the measurement of polarization by our instrument.We also introduce the radiative transfer model taking into account polarization and apply it tothe observations of a phenomenon called glory which allows to characterize the properties of thecloud droplets. We will then invesigate the variability of the haze layers lying above the maincloud deck.
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Loïc Rossi. Étude des nuages de Vénus par polarimétrie avec les données de l’instrument SPICAV-IR à bord de Venus Express. Planétologie et astrophysique de la terre [astro-ph.EP]. Université de Versailles-Saint Quentin en Yvelines, 2015. Français. ⟨NNT : 2015VERS041V⟩. ⟨tel-01327236v2⟩

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