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Caractérisation des propriétés physiques de la surface de Mars à partir de mesures spectro-photométriques orbitales

Abstract : The PhD work focuses on the characterization of geological processes on planetary surfaces. Due to the lack of broad scale in situ information about the surface physical properties of the Martian materials (recording the geological processes), my work centers on the development and validation of an approach for their estimation from orbital spaceborne datasets. In addition, determining the physical properties has an implication for the spectroscopic interpretation notably for the mineral abundances. More specifically, I developed an approach for the determination and the analysis of the Martian surface scattering properties using CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) observations [Murchie et al., 2007] on-board MRO (Mars Reconnaissance Orbiter). CRISM provides multi-angular (varied emission angles) hyperspectral images which allow the characterization of the surface scattering behavior at ∼200m/pixel. The scattering behavior depends on the material composition but also the physical properties such as the grain size, shape, internal structure, and the surface roughness / porosity. The main objective is to observe the spatial variations of the surface scattering properties and the photometric parameters as a function of geological units.The methodology I employ is based on the estimation of the surface photometric parameters in term of surface physical properties. After an atmospheric correction (aerosols) by the Multi-angle Approach for Retrieval of the Surface Reflectance from CRISM Observations (MARS-ReCO) [Ceamanos et al., 2013] developed in collaboration with X. Ceamanos and S. Douté (IPAG, France), I analyze the surface reflectance taken at varied geometries by inverting the Hapke photometric model [Hapke, 1993] depending on six parameters (single scattering albedo, 2-term phase function, macroscopic roughness and 2-term opposition effects parameters) in a Bayesian framework [Fernando et al., 2013]. The algorithm for the correction for the aerosols and the methodology for the estimates of surface photometric parameters have been validated by comparing the results from orbit to the in situ photometric measurements from Mars Exploration Rover (MER) rovers [Fernando et al. 2013].The MER landing sites located at Gusev Crater and Meridiani Planum provide an excellent opportunity to ground truth and validate the interpretation of derived Hapke photometric parameters as both orbital and in situ data are readily available over numerous geological terrains. Orbital results are consistent with the in situ observations. In my work, I mapped the surface scattering properties in and around the rover path, providing extended information over a wider area. Significant variations in the scattering properties are observed inside a CRISM observation (10x10km) suggesting that the surfaces are controlled by local geological and climatic processes [Fernando et al., in revision].The last part of this work focuses on the determination of the surface photometric parameters of different Martian geological terrains under different contexts in order to identify variabilities of the scattering properties
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Jennifer Fernando. Caractérisation des propriétés physiques de la surface de Mars à partir de mesures spectro-photométriques orbitales. Planétologie et astrophysique de la terre [astro-ph.EP]. Université Paris Sud - Paris XI, 2014. Français. ⟨NNT : 2014PA112293⟩. ⟨tel-01152136⟩

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