The CRAPS on Mars project aims to develop and evaluate a strategy of combined analysis of LIBS and Raman spectra that will be beneficial to the SuperCam team. This ambitious project holds on many pillars described hereafter.
Selection of carbonates : The selection of terrestrial carbonates to be analyzed is a crucial step of this project and is expected to represent the various geological contexts of formation of the Martian carbonates.The access to the collections of different laboratories in Earth Science and museums partners will allow to get reference rocks already characterized by other techniques. In complement, standard reference samples and replicates of the calibration targets onboard the Mars 2020 rover will complete this corpus of samples in order to consider in the present project an exhaustive collection of carbonates. The analysis of these samples aims to interpret the results from the data collected by SuperCam to answer the question of the origin of the Martian carbonates (hydrothermal, sedimentary, volcanic…) and help the reading of the geological site.
SuperCam+ : ideal laboratory tool : The CELIA lab is nowadays equipped with a pulsed laser operating at 1064 nm and 532 nm for LIBS and Raman spectroscopies, respectively. Both types of spectra can be recorded with time-gated conditions thanks to the use of an intensified CCD camera. Consequently, the experimental conditions accessible at CELIA not only allow to mimic the ones of SuperCam but also to go further and to explore and assess extra experimental conditions. One can mention the control of the polarization for Raman and the exploration of very short acquisition times for both LIBS and Raman. The SuperCam+ facility will thus be a real technical support for the calibration prior to launching and also for interpreting SuperCam data. This facility and the PhD research program altogether will also enrich the scientific works dedicated to the interpretation of spectra.
Considering LIBS, special attention will be paid to a selection of elements playing a key-role on the determination of carbonates, namely Ca-Mg-Fe-Mn, and Sr as trace element. In the case of Raman, it is anticipated that the substituting ions inside the crystalline matrix should have the main influence for the determination of the samples mineralogy (CaCO3, FeMg(CO3)2, …).
Correlative spectra analysis : Looking for correlation between Raman and LIBS data can be declined along two directions. The first one consists in developing a strategy of numerical analysis of the spectra, based on chemometric tools allowing multivariate approaches. Several chemometric tools have also been successfully applied to LIBS and are easily transposable to the Raman analysis. At the opposite, the combined LIBS/Raman analysis is definitely challenging, not only regarding its development but also its assessment. The second direction consists in performing a series of parametric experiments in order to evaluate the influence of the experimental conditions on the correlation of spectra. To illustrate, the time-gating will be particularly considered and the representativeness of the data will be studied according to the mineralogical variability of a single sample at the scale of the Raman and LIBS spots size. The objective is clearly to interpret, through this new correlative approach, high quality experimental data. Thus, the LIBS/Raman correlative approach will provide information about the type of cations involved in the formation and the molecular assemblies of the carbonated structure. More generally, this correlative approach opens the path to a new methodology of data fusion for interpreting a large number of data originating from various instruments.
In conclusion, at the opposite of the CRAPS game played in the North-American casinos, the CRAPS on Mars project does not relate to random or chance but it is supported by a realistic scientific program.
Master en Physique (laser, matière, et nanosciences ou équivalent ) ou en Physico-chimie.
Goût avéré pour les expériences de spectroscopie laser et pour les techniques de chimiométrie destinées au traitement des données par des approches multivariées.
IGrande aptitude pour le travail en équipe et s'investira tout particulièrement dans les aspects interdisciplinaires de son travail de thèse allant de la physique à la géochimie, en passant par l'analyse des spectres, grâce à l'environnement de l'équipe Supercam dont il bénéficiera.
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