La planète Mars est le siège d'un climat complexe, caractérisé par des cycles du dioxyde de carbone et de l'eau, ainsi qu'un transport de poussière à toutes les échelles. Ces cycles se manifestent par la condensation saisonnière aux pôles de dépôts de glace de CO₂ et d'eau pendant la nuit polaire, et leur sublimation pendant le printemps local. Les cycles du CO₂ , de l'eau et des poussières sur Mars sont intimement liés. Un processus saisonnier actif illustre bien ces liens : les jets de gaz froid, déclenchés par la sublimation saisonnière des dépôts de CO₂ , pouvant mettre en suspension des poussières du régolite de manière durable dans l'atmosphère, et dont l'activité semble être modulée par les échanges d'eau à la surface.L'objectif de cette thèse est de permettre l'utilisation des données d'imagerie hyperspectrale disponibles au maximum de leur potentiel, pour apporter de nouvelles contraintes sur les échanges saisonniers entre surface et atmosphère et sur les interactions entre les différents cycles (CO₂ , eau, poussières), en se focalisant sur les jets de gaz froid. Pour cela, un modèle semi-analytique de transfert radiatif dans les glaces compactes, ainsi qu'une méthode efficace d'inversion ont été développés et validés.Le modèle de transfert radiatif permet de décrire l'interaction de la lumière avec une couche de glace de manière quantitative d'après les paramètres suivants : épaisseur de la couche, proportions volumiques et tailles des impuretés, rugosité de la surface. Il repose sur plusieurs hypothèses majeures : optique géométrique, milieux continus par morceaux, inclusions quasi-sphériques. L'approximation des deux flux est utilisée pour le transfert au sein de la couche mais la réflexion spéculaire en surface est estimée en tenant compte de la variabilité des facettes de la rugosité surfacique. Ce modèle a été validé numériquement et sur des données de laboratoire et des tests numériques. La méthode d'inversion consiste à créer des bases de données synthétiques d’après le modèle de transfert radiatif pour déterminer les jeux de paramètres les plus probables pour reproduire une mesure donnée. L'inversion repose sur le formalisme bayésien : les grandeurs manipulées sont décrites par des densités de probabilités. Ceci permet la prise en compte de manière réaliste des incertitudes sur la donnée et le calcul d'une incertitude a posteriori sur le résultat de l'inversion.Une étude ciblée d'un site d'intérêt a été menée pour tester et démonter l'applicabilité de cette démarche à l'inversion massive de données de spectro-imagerie.Nous avons déterminé l’état de surface du champ de dunes du cratère de Richardson (72°S, 180°W), choisi car il présente de fortes interactions entre cycle de l'eau et du CO₂ , une important activité saisonnière de jets froids mais aussi une grande quantité de données disponible et une haute qualité du suivi temporel. Le suivi des caractéristiques de surface sur ce site montre une diminution de l'épaisseur de la couche de glace pendant le printemps cohérente avec les estimations des modèles de climat. Nous avons pu estimer et faire le suivi du contenu en eau et en poussière pour discuter le scénario de formation des jets froids. Nous avons proposé un nouveau mécanisme de mise en suspension des petits grains d’eau. / Mars has a complex climate, characterized by carbon dioxide and water cycles, and dust transport at all scales. These cycles are mainly controlled by the seasonal condensation of CO₂ and water ice deposits at high latitudes during the polar night and their sublimation during the local spring. There are a lot of interactions between the CO₂ , water and dust cycles on Mars and they influence each other. An active seasonal process illustrates particularly well these links: the cryoventing, cold CO₂ gas jets triggered by seasonal sublimation of CO₂ deposits, which can put dust from the regolith in suspension into the atmosphere durably, and whose activity seems to be modulated by the exchange of water at the surface.The purpose of this thesis is to allow the use of the available hyperspectral imaging data to their full potential, to bring new constraints on seasonal exchanges between surface and atmosphere and the interactions between the different cycles (CO₂ , water , dust), focusing on cold gas jets. To achieve this, a semi-analytical radiative transfer model in compact ices and an effective inversion method were developed and validated.The radiative transfer model describes the interaction of light with a surface quantitatively, using the following parameters: thickness of the layer, volume proportions and grain-sizes of impurities, surface roughness. It is based on several key assumptions: geometrical optics, piecewise-continuous media quasi-spherical inclusions. The two-stream approximation is used for the radiative transfer inside the layer, but the surface specular reflectance is estimated taking into account the variability of the facets orientations from the surface roughness. This model was validated both numerically and on laboratory data.The inversion method consists in exploring synthetic databases generated by the radiative transfer model and determining the most likely sets of parameters to reproduce a given measure. The inversion is based on the Bayesian formalism: the manipulated variables are described by probability density functions. This allows to take into account realistic uncertainties on the data and enables to calculate a posteriori uncertainties on the result of the inversion.A focused study was conducted on a area of particular interest, to test and prove the applicability of this approach to the massive inversion of spectro-imaging data. The dune-field of Richardson Crater (72°S, 180°W) was chosen because it shows strong interactions between the water and CO₂ cycles, a major seasonal cryoventing activity, but also a large amount of data available and a high quality temporal monitoring. The monitoring of surface characteristics on this site shows a decrease in the thickness of the ice during the spring consistently with climate models simulations. We were able to estimate and monitor the content of water and dust in order to discuss the formation scenario of cold jets.

The development and application of new cloud retrieval methods from ground–based and airborne measurements of spectral radiance fields above heteorogeneous surfaces is introduced. The potential of imaging spectrometers in remote–sensing applications is evaluated. The analyzed spectral radiance fields were measured during two international field campaigns in the visible wavelength range (400–970 nm) with high spatial (<10m) resolution. From ground–based measurements, high ice clouds were observed and from airborne measurements Arctic stratus. From the measurements, cloud optical thickness is retrieved with high spatial resolution and the horizontal cloud inhomogeneities are investigated. Depending on the measurement configuration, different uncertainties arise for the retrieval of the cloud optical thickness. A reduction of those uncertainties is derived by a specification of the ice crystal shape to improve the retrieval of the optical thickness of high ice clouds. The ice crystal shape is obtained independently from the angular information of the scattering phase function features, imprinted in the radiance fields. A performed sensitivity study reveals uncertainties of up to 90%, when neglecting this information and applying a wrong crystal shape to the retrieval. For remote-sensing of Arctic stratus, the highly variable surface albedo influences the accuracy of the cloud optical thickness retrieval. In cloudy cases the transition of reflected radiance from open water to sea ice is not instantaneous but horizontally smoothed. In general, clouds reduce the reflected radiance above bright surfaces in the vicinity of open water, while it is enhanced above open sea. This results in an overestimation of to up to 90% in retrievals of the optical thickness. This effect is investigated. Using observations and three-dimensional radiative transfer simulations, this effect is quantified to range to up to 2200 m distance to the sea-ice edge (for dark-ocean albedo of αwater = 0.042 and sea-ice albedo of αice = 0.91 at 645 nm wavelength) and to depend on macrophysical cloud and sea-ice properties. The retrieved fields of cloud optical thickness are statistically investigated. Auto–correlation functions and power spectral density analysis reveal that in case of clouds with prevailing directional cloud structures, cloud inhomogeneities cannot be described by a universally valid parameter. They have to be defined along and across the prevailing cloud structures to avoid uncertainties up to 85%. / Im folgenden wird die Entwicklung und Anwendung neuer Ableitungsverfahren von Wolkenparametern, basierend auf bodengebundener und flugzeuggetragener spektraler Strahldichtemessungen über heterogenen Untergründen, vorgestellt und das Fernerkundungspotential abbildender Spektrometer evaluiert. Die spektralen Strahldichtefelder wurden während zweier internationaler Feldkampagnen im sichtbaren Wellenlängenbereich (400–970 nm) mit hoher räumlich Auflösung (<10m) gemessen. Bodengebundene Messungen wurden genutzt, um hohe Eiswolken zu beobachten und flugzeuggetragenen um arktischen Stratus zu beobachten. Aus den Messungen werden räumlich hochaufgelöste wolkenoptische Dicken abgeleitet und anschließend horizontale Wolkeninhomogenitäten untersucht. Die Ableitung der wolkenoptischen Dicke birgt je nach Messkonfiguration verschiedene Unsicherheiten. Eine Reduzierung der Unsicherheiten wird durch die Vorgabe einer Eiskristallform zur Verbesserung der Ableitung der optischen Dicke hoher Eiswolken erreicht. Diese werden unabhängig aus den winkelabhängigen, in das gemessene Strahldichtefeld eingeprägten Eigenschaften der Streuphasenfunktion, abgeleitet. Bei Vernachlässigung dieser Information und Wahl der falschen Eiskristallform, treten Fehler in der abgeleiteten optischen Dicke von bis zu 90% auf. Bei der Fernerkundung von arktischem Stratus beeinflusst die sehr variable Bodenalbedo die Genauigkeit der Ableitung der optischen Dicke. Beim Übergang von Meereis zu Wasser, findet die Abnahme der reflektierten Strahldichte im bewölktem Fall nicht direkt über der Eiskante, sondern horizontal geglättet statt. Allgemein reduzieren Wolken die reflektierte Strahldichte über Eisflächen nahe Wasser, während sie über dem Wasser erhöht wird. Dies führt zur Überschätzung der wolkenoptischen Dicke über Wasserflächen nahe Eiskanten von bis zu 90 %. Dieser Effekt wird mit Hilfe von Beobachtungen und dreidimensionalen Strahlungstransferrechnungen untersucht und es wird gezeigt, dass sein Einfluss noch bis zu 2200 m Entfernung zur Eiskante wirkt (für Meeresalbedo 0.042 und Meereisalbedo 0.91 bei 645 nm Wellenlänge) und von den makrophysikalischen Wolken- und Meereiseigenschaften abhängt. Die abgeleiteten Felder der optischen Dicke werden statistisch ausgewertet, um die Inhomogeneität der Wolken zu charakterisieren. Autokorrelationsfunktionen und Leistungsdichtespektren zeigen, dass Inhomogenitäten von Wolken mit vorranging richtungsabhängiger Struktur nicht mit einem allgemeingültigen Parameter beschrieben werden können. Es sind Inhomogenitätsmaße entlang und entgegen der jeweiligen Wolkenstrukturen nötig, um Fehler von bis zu 85% zu vermeiden.

Tropical forests, which provide important ecosystem functions and services, are increasingly threatened by anthropogenic pressures. This has resulted in an urgent need to understand tree species diversity of those forests. Where knowledge of that diversity is largely from the botanical surveys and local ecological studies, data must inevitably be up-scaled from point observations to the landscape and regional level if a holistic perspective is required. This thesis explores aspects of the spatio-temporal heterogeneity of canopy reflectance patterns over the forests of French Guiana, in order to assess whether this information could help defining an ecologically consistent forest typology. To gain insight into both the spatial and temporal heterogeneity of French Guiana’s forests, instrumental artefacts affecting the satellite data first had to be addressed. Data used in this study represent the spectral response of forest canopies, and the way in which such data are captured makes them susceptible to the ‘bi-directional reflectance distribution function’ (BRDF). BRDF indicates that objects do not reflect light in equal proportions in all directions (isotropically). Thus, forest canopies will reflect light anisotropically depending on factors including canopy roughness, leaf optical properties and inclination, and the position of the sun relative to the sensor. The second chapter of this thesis examines how BRDF affects the canopy reflectance of forests in French Guiana, and how not correcting for BRDF affects spectral classifications of those forests. When monthly reflectance data corrected for the artefact are examined, these suggest seasonally-occurring changes in forest structure or spectral properties of French Guiana’s forests. The third chapter of this thesis thus examines temporal effects of BRDF, and used cross-regional comparisons and plot-level radiative transfer modelling to seek to understand the drivers of the monthly variation of the forests’ canopy reflectance. For the latter, the Discrete Anisotropic Radiative Transfer (DART) model was used along with aerial laser scanning (ALS) observations over different forest structures, indicating that the observed variation in reflectance (and derivatives known as vegetation indices) could not be explained by monthly variations in solar direction. At the regional scale, it was also demonstrated that forests in the Guiana Shield possess temporal variation distinct from forests in central Africa or northern Borneo, forests also lying just above the Equator. Had the observed temporal variation in vegetation indices been the result of BRDF, it would have been expected that the forests in the three zones would have similar patterns of variation, which they did not. Central African forests appear to have their greening synchronized with rainfall, whereas forests in the Guianas appear synchronized with the availability of solar radiation. Further analysis of the vegetation index time-series of observations also indicated that different types of forests in French Guiana possess distinct patterns of temporal variation, suggesting that tropical forest types can be discriminated on the basis of their respective “temporal signatures.” That was exploited in the fourth chapter of the thesis, which maps forests in French Guiana based on their combined spatio-temporal canopy reflectance patterns and by so doing presents a novel way of addressing forest typology, based on ecologically meaningful information. The thesis presented demonstrates that it is possible to adequately address remote sensing data artefacts to examine patterns of spatial and temporal variation in tropical forests. It has shown that phenological patterns of tropical rainforests can be deduced from remote sensing data, and that forest types can be mapped based on spatio-temporal canopy reflectance patterns. It is thus an important contribution to understand the ecology of tropical forests in French Guiana and to improve the toolbox of scientists dealing with the identification of spatio-temporal patterns observable in forests at the landscape level.

In der vorliegenden Arbeit werden optische Schichteigenschaften von Zirren durch räumlich und zeitlich kombinierte flugzeuggetragene Messungen zusammen mit Strahlungstransfersimulationen untersucht. Diese räumlich koordinierten Strahlungs– und Mikrophysikmessungen oberhalb, unterhalb und innerhalb des Zirrus werden mittels eines Forschungsflugzeuges (Learjet 35A) in Kombination mit einem Schleppkörper namens AIRTOSS (AIRcraft TOwed Sensor Shuttle) realisiert. AIRTOSS wird dabei vom Flugzeug aus mittels einer Winde abgelassen und wieder eingeholt. Die maximale Seillänge beträgt 4 km. Im Rahmen des AIRTOSS–ICE–Projekts (Inhomogeneous Cirrus Experiment) wurden während zweier Messkampagnen über der Nord– und Ostsee im Frühjahr und Spätsommer 2013 flugzeuggetragene Beobachtungen der Zirruseigenschaften durchgeführt. Beispielmessungen eines Messfluges werden in dieser Arbeit gezeigt, welche den Nutzen der simultanen Strahlungsmessungen mittels zweier Messplattformen aufzeigen. Aus den Messungen der spektralen Flussdichten oberhalb und unterhalb des Zirrus werden die optischen Schichteigenschaften wie Transmissivität, Reflektivität und Absorptivität und die Albedo der Wolkenschicht ermittelt. Die flugzeuggetragenen Untersuchungen werden durch Sensitivitätsstudien gestützt, basierend auf einem eindimensionalen Strahlungstransfermodell. Dies dient der Charaktierisierung des Einflusses variierender, optischer und mikrophysikalischer Zirruseigenschaften (Eiskristallform, Partikelgröße und optische Dicke) auf die optischen Schichteigenschaften und den solaren Strahlungsantrieb des Zirrus. Weitere Studien zeigen den Einfluss einer darunterliegenden Flüssigwasserwolke auf die Zirruseigenschaften. Eine niedrige Wolkenschicht führt zu Abweichungen der Schichteigenschaften des Zirrus von 85%. Die Nichtberücksichtigung niedriger Wolken unterhalb einer Zirrusschicht führt zu einer deutlichen Überschätzung des Strahlungsantriebs des Zirrus um Faktor 5. / In this thesis cirrus optical layer properties are investigated by truly collocated measurements and supplementary radiative transfer simulations. The close collocation of the radiative and microphysical measurements, above, beneath and inside the cirrus, is obtained by using a research aircraft (Learjet 35A) in tandem with a towed platform called AIRTOSS (AIRcraft TOwed Sensor Shuttle). AIRTOSS can be released from and retracted back to the research aircraft by means of a cable up to a distance of 4 km. Data were collected in two field campaigns above the North and Baltic Sea in spring and late summer 2013 in the framework of the AIRTOSS–ICE (AIRTOSS – Inhomogeneous Cirrus Experiment) project. Exemplary, results from one measuring flight are discussed also to illustrate the benefits of collocated sampling. The spectral optical layer properties of cirrus are derived from simultaneous and vertically collocated measurements of spectral upward and downward solar irradiance above and below the cloud layer and concurrent in situ microphysical sampling of the ice particle size distributions. From the irradiance data the optical layer properties (transmissivity, reflectivity, and absorptivity) and the cloud top albedo of the observed cirrus layer are obtained. These airborne observations are supported by sensitivity studies using one–dimensional radiative transfer modelling to characterize the effect of varying cirrus optical and microphysical properties (ice crystal shape, particle size, and cloud optical thickness) on the cirrus optical layer properties, as well as on the solar cirrus radiative forcing. Further studies show the impact of an underlying low–level liquid water cloud on the mentioned cirrus properties. A low–level cloud causes differences in the layer properties of the cirrus by 85%. If low–level clouds below cirrus are not considered the solar cooling due to the cirrus is significantly overestimated by up to a factor of 5.

En physique du transport, en particulier en physique du transfert radiatif, la méthode de Monte-Carlo a été développée à l'origine comme la simulation de l'histoire d'un grand nombre de particules, dont on déduit des observables moyennes. Cette méthode numérique doit son succès à plusieurs qualités : une gestion naturelle des espaces des phases aux nombreuses dimensions, une erreur systématique nulle par rapport au modèle physico-mathématique, les intervalles de confiance donnés avec les résultats, une capacité à prendre en compte simultanément de nombreux phénomènes physiques, la possibilité de calcul de sensibilités simultané, et une parallélisation aisée. En cinétique des gaz, les particules collisionnent entre elles et non pas avec un milieu extérieur ; on dit que leur transport est non-linéaire. Ces collisions mutuelles mettent en défaut l'approche évoquée ci-dessus de la méthode de Monte-Carlo ; car pour simuler des trajectoires indépendantes de multiples particules et ainsi estimer leur distribution, il faut connaître au préalable exactement cette même distribution...Cette thèse fait suite à celles de Jérémi DAUCHET (2012) et de Mathieu GALTIER (2014), consacrées au transfert radiatif. Entre autres travaux, ces auteurs montraient comment la méthode de Monte-Carlo peut s'accommoder de non-linéarités, en gardant son formalisme et ses spécificités habituelles. Les non-linéarités alors franchies étaient respectivement une loi de couplage chimie/luminance, et la dépendance de la luminance envers le coefficient d'absorption. On essaie dans ce manuscrit d'outrepasser la non-linéarité du transport. Pour cela, nos principaux outils sont un suivi des particules en remontant le temps, basé sur des formulations intégrales des équations de transport, formulations largement inspirées des algorithmes dits à collisions nulles. Nous montrons, sur plusieurs exemples académiques, que nous avons en effet étendu la méthode de Monte-Carlo à la résolution de l'équation de Boltzmann. Ces exemples sont aussi l'occasion de tester les limites de ce que nous avons mis en place. Les résultats les plus marquants sont certainement l'absence totale de maillage dans la méthode numérique, ainsi que sa capacité à calculer correctement les quantités de particules de haute énergie cinétique (toujours peu nombreuses par rapport au total, en cinétique des gaz). Au-delà des exemples fournis, ce manuscrit est voulu comme un essai de formalisme et une exploration des bases de la méthode développée. L'accent est mis sur les raisonnements menant à la mise au point de la méthode, plutôt que sur les implémentations particulières qui ont été abouties. La méthode est encore, aux yeux de l'auteur, largement susceptible d'être retravaillée. En particulier, les temps maximaux sur lesquels l'évolution des particules est calculable, qui constituent la faiblesse principale de la méthode numérique développée, peuvent sûrement être augmentés. / In transport physics, especially in radiative transfer physics, the Monte-Carlo method has been originally developed as the simulation of the history of numerous particles, from which are deduced mean observables. This numerical method owes its success to several qualities : a natural management of many-dimensional phase space, a null systematic error away from the mathematical and physical model, the confidence intervals given with the results, an ability to take into account simultaneously numerous physical phenomenons, the simultaneous sensitivities calculating possibility, and an easy parallelization. In gas kinetics, particles collide each other, not with an external fixed medium ; it is said that their transport is non-linear. These mutual collisions put out of action the aforesaid approach of the Monte-Carlo method ; because in order to simulate the independent trajectories of multiple particles and thus estimate their distribution, this distribution must beforehand be exactly known...This thesis follows on from those of Jérémy DAUCHET (2012) and of Mathieu GALTIER (2014), dedicated to radiative transfer physics. Between other works, these authors have shown how the Monte-Carlo method can bear non-linearities, while keeping its customary formalism and specificities. The then overcome non-linearities were respectively a chemistry/irradiance coupling law, and the dependence of the irradiance toward the absorption coefficient. We try in this manuscript to overcome the non-linearity of the transport. In this aim, our main tools are a reverse following of particles, based on integral formulations of the transport equations, formulations largely inspired from the so-called null collisions algorithms. We show, on several academic examples, that we have indeed extended the Monte Carlo method to the resolution of the Boltzmann equation. These examples are also occasions to test the limits of what we have built. The most noteworthy results are certainly the absence of any mesh in the numerical method, and its capacity to calculate correctly the high-speed particles quantities (always rare compared to the total, in gas kinetics). Beyond the given examples, this manuscript is wanted as a formalism attempt and an exploration of the developed method basics. The focus is made on the reasoning leading to the method, rather than on particular implementations which have been realized. In the eyes of the author, the method is still largely reworkable. In particular, the maximal times on which the evolution of particles is computable, which constitute the main weakness of the developed numerical method, can surely be increased.

The K-distribution method is a fast approximative method used for calculating thermal infrared radiative transfer in the atmosphere, as opposed to the traditional Line-by-line method, which is precise, but very time-costly. Here we consider the atmosphere to consist of homogeneous and plane-parallel layers in local thermal equilibrium. This lets us use efficient upwards recursion for calculating the thermal infrared radiative transfer and ultimately the outgoing irradiance at the top of the atmosphere. Our specific implementation of the K-distribution method revolves around changing the integration space from the wavenumber domain to the g domain by employing Gauss-Legendre quadrature in two steps. The method is implemented in MATLAB and is shown to be several thousand times faster than the traditional Line-by-line method, with the relative error being only 3 % for the outgoing irradiance at the top of the atmosphere.

L'objectif de ce projet de recherche est la mise au point et l'utilisation de charges inorganiques barrière aux rayonnements infrarouge pour la préparation de matériaux d'enduction à base de plastisols PVC. Dans un premier temps, cette étude a été consacrée à la caractérisation rhéologique, morphologique et optique de la matrice PVC et à l'élaboration de nouvelles formulations, en incorporant dans le plastisol des charges commerciales de natures chimiques différentes (nacre, billes de verre, alumine, oxyde de Zinc, TiO2 …). Ensuite, des mesures radiatives sur des films de plastisols chargés à différents taux massiques ont été réalisées dans le but de sélectionner les charges présentant les meilleures performances optiques. Enfin, les formulations optimales ont été enduites sur un textile polyester et la stabilité des revêtements soumis à des rayonnements UV a été suivie par plusieurs techniques analytiques. Diverses caractérisations mécaniques, esthétiques et morphologiques sont venues compléter cette étude. Dans un second temps, un modèle de transfert radiatif permettant de simuler la propagation du rayonnement dans les systèmes de protection développés a été testé / This project aims to develop new filled PVC plastisol composite offering enhanced optical properties. Different types of inorganic fillers were tested and added to the PVC matrix. Rheological, morphological and optical characterization of the PVC matrix and development of new formulations by incorporation of different fillers (nacre, glass beads, alumina, zinc oxide, TiO2 ...) were the subject of the first phase of the project. Then, radiative measurements on plastisol films loaded at different mass ratios were performed in order to select the fillers having the best optical performance. The second phase was dedicated to the validation and the testing of the optimal formulations coated on polyester textile substrate. Different analytic technics were used in order to rank the UV stabilization as a function of the tested formulations. In addition, mechanical, aesthetic and morphological characterizations were used to complete this study. Finally, radiative transfer model was developed to simulate the radiative behavior of the different formulations

Indiana University-Purdue University Indianapolis (IUPUI) / This dissertation focuses on quantification of submicroscopic iron of different sizes, mineral abundance and grain size of lunar soils using Hapke's radiative transfer model. The main objective is to explore implications of these results for assessing the relative importance of solar wind implantation versus micrometeorite impacts for lunar space weathering as well as three hypotheses (solar wind deflection, comet impact and dust transport) for swirl formation on the Moon. Results from this study can help to make connections between ordinary chondritic meteorites and asteroids, and put physical and chemical constraints on heating processes in the early solar system.

Wegen der zunehmenden Menge an LIBS-Daten von der Marsoberfläche sowie deren speziellen Herausforderungen bei der Analyse untersucht diese Arbeit, wie die Modellierung und Simulation von solchen LIBS-Spektren genutzt werden kann. Das Ziel ist es, Einblicke in die Eigenschaften von LIBS-Plasmen auf dem Mars zu erhalten und Modelle zu entwickeln, die bei der Analyse von realen Missionsdaten helfen können. Die Modellierung basiert sich auf einem stationären Plasma im lokalen thermischen Gleichgewicht (LTE). Das Plasma wird dabei in eine Reihe homogener Zonen unterteilt und Spektren werden mit dem Strahlungstransfer entlang einer eindimensionalen Sichtlinie durch diese Plasmazonen simuliert. Die Ergebnisse dieser Arbeit zeigen, dass auf LTE basierende Modelle gut auf LIBS-Spektren angewendet werden können, die unter Marsbedingungen gemessen wurden. Für zeitaufgelöste Daten kann die Anpassung eines Zwei-Zonen-Modells verwendet werden, um Einblicke in das Plasma zu erhalten und um die Elementkonzentrationen mit einer höheren Genauigkeit zu bestimmen, als es mit der Saha-Boltzmann-Methode möglich wäre. Allerdings sollten Nicht-Gleichgewichtseffekte in den frühesten und spätesten Phasen der Plasmalebensdauer berücksichtigt werden. Für zeitlich integrierte Spektren, wie sie bei aktuellen Marsmissionen gemessen werden, sind Anpassungen durch ein Zwei-Zonen-Modell aufgrund von zu langen Rechenzeiten nicht durchführbar. Stattdessen kann durch die Methode der spektralen Entmischung eine Überlagerung von Spektren unterschiedlicher Temperaturen und Dichten verwendet werden. Diese Methode ermöglicht keine direkten quantitativen Bestimmungen der Elementkonzentrationen, ist aber ein hervorragendes Werkzeug, um einen Überblick über die große Menge an Informationen zu erhalten, die in den Spektren enthalten sind. / Motivated by existing challenges in analysing LIBS spectra and the increasing quantity of Martian LIBS data, this thesis investigates the modelling and simulation of LIBS spectra for the application to LIBS data in Martian atmospheric conditions. This is done with the aim of providing insights into the characteristics of Martian LIBS plasmas as well as developing tools to assist the analysis of real mission data. The modelling of LIBS spectra is based on a stationary plasma in local thermal equilibrium (LTE). The plasma is then divided into a series of homogeneous zones and spectra are simulated using radiative transfer along a one-dimensional line-of-sight through the plasma zones. The results of this thesis show that spectral modelling based on LTE can be well applied to LIBS data in Martian atmospheric conditions. For time-resolved data, fits of a two-zone plasma model can be used to obtain insights into the plasma as well as improved concentration estimates compared to the Saha-Boltzmann plot method. However, attention to non-equilibrium effects should be given at the earliest and latest stages of the plasma lifetime. For time-integrated spectra, i.e. real mission data, fits of the two-zone model are not feasible due to too long computation times. Instead, a superposition of spectra of different temperatures and densities, i.e. the spectral unmixing method, can be used. Although not directly allowing for quantitative concentration estimates, the method is a great tool to overview the large amount of information contained in the spectra.

No description available.