The SuperCam Remote Sensing Instrument Suite for Mars 2020

International audienceThe Mars 2020 rover, essentially a structural twin of MSL, is being built to a) characterize the geology and history of a new landing site on Mars, b) find and characterize ancient habitable environments, c) cache samples for eventual return to Earth, and d) demonstrate in-situ production of oxygen needed for human exploration. Remote-sensing instrumentation is needed to support the first three of these goals [1]. The SuperCam instrument meets these needs with a range of instrumentation including the highest-resolution remote imaging on the rover, two different techniques for determining mineralogy , and one technique to provide elemental compositions. All of these techniques are co-boresighted, providing rapid comprehensive characterization. In addition, for targets within 7 meters of the rover the laser shock waves brush away the dust, providing cleaner surfaces for analysis. SuperCam will use an advanced version of the AEGIS robotic target selection software

The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description

On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds

Tomographie optique diffuse résolue en temps (Applications fonctionnelles en neurosciences)

La tomographie optique diffuse est une nouvelle modalité d'imagerie médicale fonctionnelle. Elle présente de nombreux atouts pour le suivi de l'activité cérébrale. Dans ce contexte, ces travaux s'articulent autour de la compréhension de la propagation lumineuse au travers de la tête par l'intermédiaire de simulations fondées sur la résolution de l'équation de diffusion par la méthode des éléments finis sur des modèles anatomiques issus de la segmentation d'IRM. Nous avons mis en évidence la faible pénétration cérébrale de la lumière en raison des propriétés optiques particulières de la tête, et donc la forte influence des structures anatomiques superficielles dans le signal détecté en surface. Nous avons réalisé un système fondé sur le comptage de photons résolu en temps adapté à l'environnement clinique et qui repose sur l'utilisation de diodes laser picoseconde à quatre longueurs d'onde différentes. Les performances de l'ensemble ont été optimisées en tenant compte des nombreux impératifs cliniques ce qui a permis de réaliser et d'optimiser un appareil dont le rapport signal à bruit est uniquement limité par le bruit de photons et ayant une réponse impulsionnelle de l'ordre de 100-300 ps à mi-hauteur. Ce système a permis la détection de la variation de l'activité cérébrale. L'origine cérébrale des variations d'absorption détectées à la surface a été avérée grâce à la comparaison de l'expérience avec les simulations d'activation cérébrale (B.Montcel et al. Applied Optics, 44, 1942-1947, 2005). Les résultats des simulations ont permis de proposer des méthodes originales de localisation spatiale de l'activité cérébrale fondées sur la "loi de Beer-Lambert microscopique" qui est une fonction du temps de vol des photons. Elles permettent d'obtenir une information sur la profondeur des variations de concentration d'oxy-hémoglobine et de déoxy-hémoglobine, liées à la réponse hémodynamique cérébrale, grâce aux cartes de variations de concentration résolues en temps.Diffuse optical tomography is a new modality of functional medical imaging. Its application to the study of brain activity is very promising. In this context, this work deals with understanding light propagation through the head thanks to simulations based on the diffusion equation which is solved by the finite element method on models obtained by the segmentation of MRI. These simulations show the weak penetration of light in the brain because of the particular optical properties of the head which implies a strong influence of superficial layer in the signal detected at the surface. We built a time-resolved photon counting system suited for clinical environment based on picosecond laser diodes at four different wavelengths. Its performances have been optimized considering the clinical environment. We obtained an apparatus with a shot noise limited signal to noise ratio and with and impulse response function around 100-300 ps at half maximum. This system allowed the detection of the variation of cerebral activity. The cerebral origin of the absorption variations detected at the head surface has been proved thanks to the comparison of experiments and simulations of brain activation (B.Montcel et al. Applied Optics, 44, 1942-1947, 2005). Simulations results allowed to propose original methods to spatially localize cerebral activity based on the "microscopic Beer-Lambert law" which is a function of photons time of flight. These methods allow to obtain depth-related information on the variations of oxy- and deoxy-hemoglobin concentration due to the cerebral hemodynamic response thanks to the time-resolved concentration difference maps.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Quantification des flux de nutriments apportés par les poissons migrateurs entre le milieu marin et le milieu continental : quelles réponses un modèle de distribution d'espèce peut-il apporter ?

International audienc

Reconstruction d'images obtenues par tomographie optique dans le proche infrarouge

Ce manuscrit décrit la reconstruction d'image obtenue par tomographie optique dans le proche infrarouge, résolue en temps. Cette technique qui vise à cartographier les propriétés optiques d'absorption et de diffusion réduite des tissus, est un problème non linéaire et mal posé. Pour formuler le problème direct, il est nécessaire, dans notre cas, d'utiliser une approximation de l'équation de transport de Boltzmann, l'équation de diffusion. L'emploi de la méthode des éléments finis (FEM) permet de simuler le problème direct avec une précision suffisante pour l'inversion, tout en préservant le caractère non linéaire du phénomène. La résolution du problème inverse est ramenée à un problème d'optimisation. Il s'agit de minimiser les différences entre les données expérimentales et les données simulées, en utilisant la technique de reconstruction algébrique. Afin d'optimiser la convergence, plusieurs contraintes extérieures sont décrites, telles que l'utilisation de l'IRM dans la phase de maillage, nécessaire à la FEM, ou encore l'adaptation du maillage, à partir des deux cartographies, au fur et à mesure des itérations ... Les images présentées ont été obtenues à partir des paramètres principaux, tels que l'intensité totale et le temps moyen, extraits des profils temporels mesurés. Les objets expérimentaux ont un diamètre inférieur à 4 cm et des inclusions plus absorbantes et/ou plus diffusantes.This document describes the reconstruction of images obtained with near infrared time resolved optical tomography. This technique allows to map the optical properties, absorption and reduced scattering. However, the reconstruction is a non linear and ill-posed problem. To solve the forward problem, in our case, we have to use an approximation of the Bolzmann transport equation, the diffusion equation. The Finite Element Method (FEM) allows to simulate the forward problem with sufficient accuracy to inverse the problem and preserve the non linearity of the phenomenon. Solving the inverse problem is then similar to an optimisation problem. It aims at minimising the differences between experimental and simulated data, using an algebraic reconstruction technique. To optimise the convergence, several constraints have been introduced, such as the use of MRI to initialise the mesh for the FEM, the use of an adaptative mesh, modified after each iteration as a function of the two different maps The images presented have been obtained from the first moments of the measured temporal profiles, i.e the total intensity and the meantime. The experimental objects are less than 4cm in diameter, and include heterogeneities (which are either more absorbing, or more scattering, or both than the background).STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Les poissons diadromes et les services écosystémiques : une approche transnationale pour une première estimation

International audienceDiadromous fishes are migratory and cross-border resources: they move between fresh and marine waters and their populations share individuals between river basins, crossing administrative boundaries (e.g. states, countries). Diadromous fishes are threatened by various human activities and climate change. A generalized decline has been noticed for many species with, in some cases, a climate-induced shift in the species ranges. The situation is obviously changing, causing new socio-economic and ecological interactions among territories to appear. Consequently, a transnational approach is required in Europe and elsewhere to account for and facilitate these spatial changes in fish populations through better-adapted management plans, and ease the adaptation of territories in the face of climate change. As a consequence, DiadES, a recently-funded European project, will bring together ecologists, economists and key stakeholders from the five European member states bordering the Atlantic Ocean, i.e. France, Portugal, Spain, U.K. and Ireland, to start a joint valuation of ecosystem services associated to diadromous fishes and their potential evolution under climate change. DiadES adopts the innovative approach to convert fish abundances into monetary units, thus circumventing the difficulty to orientate public decision on diadromous fish management with only observed numbers of fish or stock estimates from models. DiadES is a multi-species initiative but its methodologies will be presented through the Allis shad (Alosa alosa) case study. Among the ecosystem services provided by diadromous fishes, the transfer of matter, nutrients and energy operated by these fishes between the continental and marine domains is directly connected to food-web functioning and thus to ecosystem state (Limburg and Waldman, 2009). Even being a widely recognized process, few quantitative estimates of this fish-based nutrient flows exist. The application of the mechanistic species distribution model (GR3D) could help in estimating such transfer at large spatial scale and under past, present and future climatic conditions. Allis shad (Alosa alosa), and its American counterpart, the American shad (Alosa sapidissima), could benefit of such model-based estimates, with arising conclusions on fish and ecosystem management being strengthened by this comparative approach