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École doctorale Sciences de l'univers, de l'environnement et de l'espace (Toulouse)

Overview
Works: 390 works in 678 publications in 2 languages and 679 library holdings
Roles: Other, Degree grantor, 996
Publication Timeline
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Most widely held works by de l'environnement et de l'espace (Toulouse) École doctorale Sciences de l'univers
Enveloppes circumstellaires des étoiles chaudes actives : modélisation et observations à haute résolution angulaire du phénomène Be et B[e] by Jamal Bittar( )

2 editions published in 2001 in French and held by 4 WorldCat member libraries worldwide

Etude de la circulation océanique en Méditerranée Occidentale à l'aide d'un modèle numérique à haute résolution : influence de la submésoéchelle by Pierre Damien( Book )

3 editions published in 2015 in French and held by 3 WorldCat member libraries worldwide

The North Western Mediterranean Sea is one of the few regions in the world where open-ocean deep convection occurs. The local cyclonic circulation brings weakly stratified waters close to the surface, that can, under special atmospheric conditions (winter strong cold winds and high heat loss rates), lead to vertical diapycnal mixing. This convection phenomenon is the origin of newly formed winter waters: Winter Intermediate Water (WIW) and new Western Mediterranean Deep Waters (nWMDW). When the strong forcing stops, the restratification of the mixed patch occurs by lateral advection of surrounding lighter waters. Mesoscale and submesoscale structures play an important role during these events, both by the sinking and the spreading of the new water formed. The SYMPHONIE model was implemented at 1km resolution over the north-western Mediterranean where recent convective years were simulated. The first objective was to review the capabilities of the high resolution model to reproduce the oceanic response to strong atmospheric cooling in terms of water formation and to resolve the submesoscale structures. To do so, comparisons were performed with the available data set. The activity of the small scale structures and the role they played were highlighted in a context of winter mixed layer deepening. The ageostrophic dynamic developed by submesoscale contributes to the enhancement of vertical velocities and lateral dispersion of properties leading to a global increase of surface layer density. As a consequence, the dense water formation and the ventilation of the deep basin is favored. For the first time, the formation of Submesoscale Coherent Vortices (SCVs) during deep convection events was documented in a realistic high resolution numerical simulation of the oceanic circulation in the north-western Mediterranean Sea. Anticyclonic and cyclonic eddies were formed presenting lifetimes exceeding one year and reflecting very slow diffusive processes between their core and their surroundings. These eddies were typical of SCVs observed in deep convection areas so far, which were found to participate in the spreading of a significant proportion (30%) of the newly formed waters and were of much importance for the ventilation of the deep basin
Analysis of the interstellar dust polarized emission with the Planck Satellite Survey data by Dana Alina( Book )

3 editions published in 2015 in English and held by 3 WorldCat member libraries worldwide

Cette thèse est dédiée à l'étude de la polarisation de la poussière interstellaire et est principalement basée sur l'analyse des données du satellite Planck. Tout d'abord, nous caractérisons le biais sur les paramètres de polarisation déduits des données. Nous avons mis en évidence que ce biais dépend non seulement du niveau de bruit, mais également de la corrélation entre les bruits sur les paramètres de Stokes. Nous avons développé des méthodes optimisées d'estimation de la fraction de polarisation, de l'angle de polarisation et de la fonction de dispersion de l'angle de polarisation, qui tiennent compte de la forme des matrices de covariance du bruit. Nous avons montré pour la première fois que le comportement du biais sur la fonction de dispersion d'angle est non trivial, et nous avons proposé une méthode pour évaluer la limite supérieure du biais que nous avons appliqué aux données Planck de la bande à 353 GHz. Nous avons étudié la corrélation entre la fraction de polarisation et la fonction de dispersion d'angle, ainsi que la corrélation entre la fraction de polarisation et la densité de colonne de gaz, sur de grandes fractions du ciel. Ceci nous a permis de mettre en évidence que la structure à 3 dimensions du champ magnétique affecte fortement la fraction de polarisation observée. Lorsque la direction du champ magnétique change le long de la ligne de visée ou dans le faisceau du télescope, on observe que la fraction de polarisation diminue. Nous avons comparé ce résultat à des simulations numériques basées sur la MHD magnétohydrodynamique). Une dépendance similaire de la fraction de polarisation avec la géométrie du champ magnétique y est observée. La diminution de la fraction de polarisation avec la densité de colonne était observée dans les nuages moléculaires dans des études précédentes. Nous avons généralisé ce résultat comme étant également caractéristique du milieu diffus à grande échelle. En combinaison avec les résultats des simulations MHD où un comportement similaire est observé, ceci indique que la diminution de la fraction de polarisation est principalement due aux changements de direction du champ magnétique le long de la ligne de visée. Nous avons pour la première fois déterminé la limite inférieure de la fraction de polarisation maximale réelle bservée avec Planck. Cette limite pourrait correspondre au niveau de polarisation intrinsèque de la poussière interstellaire dans les conditions les plus favorables de la géométrie du champ magnétique. De plus, la comparaison entre la polarisation en émission et en extinction nous a permis d'établir le rapport entre la fraction de polarisation dans les domaines sub-millimétrique et visible. Ce résultat apporte une contrainte forte pour de futurs modèles de la poussière interstellaire. Enfin, nous avons effectué une étude préliminaire sur les propriétés en polarisation des associations de coeurs froid détectés avec Planck. Cette analyse statistique nous permet de confirmer la diminution de la fraction de polarisation dans ces milieux, par rapport à l'environnement local à grande échelle. Nous discutons son origine en termes de perte d'efficacité de l'alignement des grains dans ces associations de coeurs denses
Utilisation de la signature LA-ICPMS des quartz et des micas pour la reconstitution du fonctionnement d'un système magmatique et hydrothermal polyphasé. Application au complexe Sn-W d'Echassières (Massif central, France) by Loïs Monnier( Book )

3 editions published between 2018 and 2019 in French and held by 3 WorldCat member libraries worldwide

The Echassières area in the French Massif Central hosts a large number of economic to sub-economic magmatic (Sn, Li, Ta, Nb) and hydrothermal (W, Sn, Sb) mineralizations. This thesis produced new mineralogical and fluid inclusion data from various of the W-Sn mineralized hydrothermal systems, studied the trace chemical signature of several strategic gangue minerals (mostly quartz, but also micas and topaz) and processed the data using a spectrum of multivariate statistical approaches, obtained new U-Pb dating on rutile, zircon and monazite. Integration of all results made it possible to recognize the occurrence of three major mineralizing hydrothermal events in this region, which took place during three distinct periods of the variscan orogenic cycle (pre-Tournaisian, Visean and Westphalian). These mineralizations could be related to the intrusion of three distinct magmatic bodies, each with a specific paragenesis, yet, all leading to wolframite and cassiterite crystallization
Un modèle de transport et de chimie atmosphérique à grande échelle adapté aux calculateurs massivement parallèles by Alexis Praga( Book )

4 editions published between 2015 and 2016 in French and held by 3 WorldCat member libraries worldwide

Cette thèse présente un modèle bi-dimensionnel pour le transport atmosphérique à grande échelle, nommé Pangolin, conçu pour passer à l'échelle sur les achitectures parallèles. La version actuelle comporte une advection 2D ainsi qu'un schéma linéaire de chimie et servira de base pour un modèle de chimie-transport (MCT). Pour obtenir la conservation de la masse, un schéma en volume finis de type van Leer a été retenu pour l'advection et étendu au cas 2D en utilisant des opérateurs alternés. La conservation de la masse est assurée en corrigeant les vents en amont. Nous proposons une solution au problème "des pôles" de la grille régulière latitude-longitude grâce à une nouvelle grille préservant approximativement les aires des cellules et couvrant la sphère uniformément. La parallélisation du modèle se base sur l'advection et utilise un algorithme de décomposition de domaines spécialement adapté à la grille. Cela permet d'obtenir l'équilibrage de la charge de calcul avec MPI, une librairie d'échanges de messages. Pour que les performances soient à la hauteur sur les architectures parallèles actuelles et futures, les propriétés analytiques de la grille sont exploitées pour le schéma d'advection et la parallélisation en privilégiant le moindre coût des flops par rapport aux mouvement de données. Le modèle est validé sur des cas tests analytiques et comparé à des schémas de transport à l'aide d'un comparatif récemment publié. Pangolin est aussi comparé au MCT de Météo-France via un schéma linéaire d'ozone et l'utilisation de coordonnées isentropes
Les sources responsables de la réionisation vues par MUSE by David Bina( Book )

2 editions published in 2016 in French and held by 2 WorldCat member libraries worldwide

Significant efforts have been put for the past two decades to understand the formation process of structure in the early Universe. The recent technological advances in the observational field allow for observing galaxies further and further, even the ones responsible for the cosmic reionization which occurred during the first billion years of the Universe. The main goal of this thesis was to impose constraints on the nature and the abundance of the sources responsible of the cosmic reionization. More specifically, the study was focused on the star-forming galaxies that have a Lyman-alpha emission (LAE) between z ~ 3 and 6.7. This thesis has been conducted within the framework of the MUSE consortium, a brand new instrument installed on the VLT in January 2014, as part of the exploitation of the Guaranteed Time (GTO). This thesis work has enabled us to confirm the unrivalled power of MUSE concerning the detection and the study of weak extragalactic sources without any preselection. We have observed four lensing clusters which magnify the incident light and make it possible to detect faint sources, at the expense of a decrease of the volume of the observed Universe. At first we started with the study of the galaxy cluster Abell 1689 in order to build up a methodology we intend to apply on other galaxy clusters. By comparing the volume density of the detected LAEs to the luminosity functions (LF) coming from the literature, we have reached the following conclusion : the slope of the power law from the Schechter function is smaller than alpha <= -1.5, which means that the number of LAEs increases drastically towards the faint luminoities. Then we have applied the new-build method to the other galaxy clusters of our sample observed with MUSE. The LAEs we have detected and measured in this sample are roughly ten times fainter than the ones observed in blank fields thanks to the lensing effect (39 < log(Lya) < 42.5). About one third of them lacks a counterpart in the continuum up to AB ~ 28 on the HST images and couldn't have been seen on targeted surveys. The final catalog includes more than 150 LAEs, this amount has enabled us to study the contribution of the faintest ones and also the evolution of the slope according to the redshift. The results of this work seem to confirm that the slope alpha is close to -2 for all the 2.9 < z < 6.7 LAEs. Furthermore, one can notice the evolution of alpha from -1.8 to -1.95 between z ~ 3-4 and z ~ 5-7, an original result and irrespective of the data set used to complement the present sample towards the bright region of the LF. The integral of the LF allows for working out the ionizing photons density emitted by these LAEs and for determining their relative impact on the cosmic reionization. In the future, the depth of the James Webb Space Telescope (JWST) observations will improve the limits of galaxy detection, certainly up to z ~ 8. The use of near-IR spectrographs such as MOSFIRE/Keck, KMOS/VLT or the very recent EMIR/GTC already provides the confirmation of z >= 7 candidates. This thesis brought new constraints on the faint-end part of the LF of LAEs for a redshift up to z ~ 6, which represents a beginning with respect to all we can do in the coming years for redshifts up to z ~ 7-8
Recherche de Jupiters chauds autour d'étoiles jeunes by Louise Yu( Book )

2 editions published in 2019 in English and held by 2 WorldCat member libraries worldwide

The past 25 years have seen the detection of about 400 hot Jupiters (hJs), giant exoplanets similar to Jupiter but orbiting their star a hundred times closer than Jupiter does the Sun. These puzzling planets are believed to have formed far from their star before migrating inwards, however the physical processes that drive this orbital transfer are still poorly constrained by observations. This question, essential to our understanding of planetary system formation, has profound implications for the architecture of these systems, and in particular for the probability of forming planets like the Earth in the habitable zone of stars. In order to better constrain the early orbital evolution of planetary systems, we analyze data collected within the frame of the MaTYSSE programme to search for hJs around weak-line T Tauri stars (wTTSs), i.e. very young Sun-like stars that stopped accreting. The main goal of MaTYSSE is to characterize the high magnetic activity of wTTSs. This activity makes hJ detection difficult, indeed, we look for hJs with the velocimetry technique, but the strong presence of magnetic dark spots and bright plages on the surface of wTTSs adds a jitter in the radial velocities (RVs), of much greater amplitude than that expected of a hJ signature. In this thesis, we model the magnetic activity of wTTSs TAP 26 and V410 Tau and filter the activity jitter out of their RVs. We also present the MaTYSSE results for star V830 Tau, for comparison. Using Zeeman-Doppler Imaging on spectropolarimetric data sets to reconstruct surface brightness distributions and magnetic topologies, we derive spot-and-plage coverages of 10 - 18 % and field strengths of 300 - 600 G. All three stars exhibit intrinsic variability not explained by differential rotation. The activity jitter is modelled with two independent methods: deriving it from our ZDI maps, or applying Gaussian Process Regression to the raw RVs. Both methods concur on the detection of a hJ around V830 Tau and another around TAP 26. The ~2 Myr V830 Tau b has a M sin i of 0.57 ± 0.10 MJup and orbits at 0.057 ± 0.001 au from its star (orbital period 4.93 d). Due to the observing window, the orbital period of TAP 26 b cannot be uniquely determined; the case with highest likelihood is a hJ with M sin i = 1.66 ± 0.31 MJup on an orbit of semi-major axis 0.0968 ± 0.0032 au (orbital period 10.79 ± 0.14 d).[...]
Impact du forçage pluviométrique sur les inondations du fleuve Niger à Niamey : Etude à partir de données satellitaires et in-situ by Claire Cassé( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

Since the development of satellite based remote sensing in the 1970s, many missions have been dedicated to monitoring the terrestrial atmosphere and surfaces. Some of these satellites are dedicated to the Tropics with specific orbits. Megha-Tropiques (MT) is devoted to the water and energy cycle in the tropical atmosphere and provides an enhanced sampling for rainfall estimation in the tropical region. This PhD work was initiated within MT hydro-meteorological activities, with the objective of assessing the hydrological potential of satellite rainfall products in the Tropics. The world most important rivers lay in tropical areas where the in situ observation networks are deficient. Alternative information is therefore needed for water resource management and alert systems. The present work focuses on the Niger River a basin which has undergone drastic climatic variations leading to disasters such as droughts and floods. Since 1950, the Niger has been through 3 main climatic periods: a wet period (1950-1960), a long and intense drought period (1970-1980) and since 1990 a partial recovery of the rainfall. These climatic variations and the anthropic pressure, have modified the hydrological behaviour of the basin. Since 2000, the middle Niger River has been hit by an increase of floods hazards during the so-called Red flood period. In Niamey city, the highest river levels and the longest flooded period were recorded in 2003, 2010, 2012 and 2013, leading to heavy casualties and property damage. This study combines hydrological modelling and a variety of rainfall estimation products (satellite and in-situ) to meet several objectives: (i) the simulation of the Niamey Red flood and the detection of floods (during the recent period 2000-2013) (ii) the study of the propagation of satellite rainfall errors in hydrological modelling (iii) the evaluation of the role of rainfall variability, and surface conditions, in the changes of the Red flood in Niamey since the 50s. The global model ISBA-TRIP, is run with a resolution of 0.5° and 3h, and several rainfall products were used as forcing. Products derived from gauges (KRIG, CPC), pure satellite products (TAPEER, 3B42RT, CMORPH, PERSIANN) and mixed satellite products adjusted by rain gauges (3B42v7, RFE2, PERSIANN-CDR). This work confirms the hydrological potential of satellite rainfall products and proposes an original approach to overcome their biases. It highlights the need for documenting the errors associated with the rainfall products and the error structure. Finally, the hydrological modelling results since the 1950s have given a new understanding of the relative role of rainfall and surface conditions in the drastic increase of flood risk in Niamey
La question de la remédiation environnementale résultant de l'exploitation artisanale, à petite échelle du diamant : cas de l'Union du fleuve Mano by Koffi Kouadio Michel Yoboue( Book )

2 editions published in 2017 in French and held by 2 WorldCat member libraries worldwide

L'exploitation artisanale, à petite échelle du diamant se pratique dans tous les pays de l'Union du Fleuve Mano (Côte d'Ivoire, Guinée, Libéria et Sierra Leone) de façon rudimentaire et parfois de façon informelle. L'exploitation minière artisanale du diamant offre cependant une importante stratégie de subsistance aux communautés locales car elle constitue l'activité principale de la plupart des travailleurs mineurs dans l'Union du Fleuve Mano (UFM). Il ressort de nos études de terrain et des enquêtes auprès des artisans mineurs que ce type d'exploitation minière a des impacts directs sur les galeries forestières, le sol et les cours d'eau. De plus, nous montrons que la réduction des impacts environnementaux engendrés par l'exploitation artisanale, à petite échelle de diamants n'est pas ressentie comme une nécessité ni comme une préoccupation majeure au sein de la communauté des artisans mineurs. Il y a souvent de la part des artisans mineurs un manque de compréhension des problèmes environnementaux et une insuffisante capacité à y faire face, comme le révèle notre étude menée sur trois sites Bobi, Toubabouko et Tortiya en Côte d'Ivoire. Les aires protégées au titre de leurs biodiversités, qui revêtent une importance écologique et socioéconomique majeure pour les populations des pays de la région de l'UFM, subissent malheureusement des pressions importantes du fait de cette exploitation minière artisanale du diamant. D'autant que bien souvent la population des artisans mineurs des sites enquêtés se révèle être en situation socio-économique très précaire et être souvent préoccupée par sa survie dans des conditions très difficiles. Ces dernières années, le Processus de Kimberley a pris l'initiative de concentrer sa réflexion et son action sur les questions environnementales. En 2012, la Déclaration de Washington, relative à l'intégration du développement de l'extraction artisanale et à petite échelle de diamants dans la mise en application du Processus de Kimberley, a souligné l'importance de prendre en considération les ramifications et conséquences environnementales de l'extraction minière artisanale. Dans cette optique, une enquête auprès des artisans mineurs en Côte d'Ivoire et une auto-évaluation de cette déclaration effectuée en 2014 en Côte d'Ivoire ont permis de comprendre que le cadre juridique, social, institutionnel et politique, constaté dans l'État Ivoirien, n'était pas toujours adapté au règlement des problèmes sociaux des artisans mineurs ni au règlement des questions environnementales soulevées par leurs activités minières. Ce travail de diagnostic de la déclaration devrait servir de modèle aux autres États de l'UFM. Les impacts des activités minières artisanales sur l'environnement existent donc mais il semble aussi que la remédiation des sites miniers artisanaux soit possible. En effet, le secteur de l'exploitation artisanale, à petite échelle de diamants a besoin de procédures de remédiation environnementale simples et de protocoles adaptés au niveau d'éducation des artisans mineurs et de leurs réalités financières. A ce sujet, la Sierra Leone a été un terrain privilégié d'expérimentation de la remédiation des sites miniers abandonnés à travers des projets gouvernementaux et des projets pilotes comme "Life after diamonds: Land Reclamation for Agriculture and Advocacy Pilot Initiative ". Ces projets ont contribué à protéger l'environnement et à améliorer les conditions socio-économiques des exploitants miniers. Cependant ces projets de remédiation quoique salutaires, ont eu aussi des limites qui méritent d'être prises en compte dans les futures initiatives des autres pays de l'UFM
Etude des réponses temporelle et spectrale de l'instrument ECLAIRs pour la mission SVOM by Armelle Bajat( Book )

2 editions published in 2018 in French and held by 2 WorldCat member libraries worldwide

La mission Franco-chinoise SVOM (Space based multi-band Variable astronomical Object Monitor), est dédiée à l'étude des sursauts ƴ, intenses et brèves bouffées de photons en X et ƴ, associées à la formation catastrophique de trous noirs. SVOM embarquera en 2021 quatre instruments observant du visible jusqu'aux rayonnements ƴ. ECLAIRs, télescope principal, est une caméra à masque codé capable de détecter et localiser, environ 200 sursauts pendant les trois années de vie de la mission. Son plan de détection compte 6400 détecteurs CdTe à contact Schottky, qui sont regroupés en matrice de 32 formant un module. Le plan est divisé en huit secteurs électroniquement indépendants, composés chacun de 25 modules. Chaque électronique est dédiée à la lecture et au codage du temps, de la position, de la multiplicité et des énergies des événements détectés sur un secteur. La validation des fonctionnalités de l'électronique de lecture a permis de s'assurer du bon codage des événements, d'estimer les limites de l'électronique et de construire un modèle analytique de correction efficace des événements perdus. Une application à une courbe de lumière d'un sursaut brillant a permis de valider théoriquement ce modèle et des mesures réalisées sur le prototype ont permis de le valider expérimentalement. D'autre part, un modèle complet de la réponse spectrale a été construit afin de caractériser chaque détecteur pavant le secteur du prototype et d'estimer la réponse du plan de détection des photons mono-énergétiques. Les processus physiques des interactions rayonnement-matière ont été simulés ainsi qu'un modèle de perte de charges puis une convolution gaussienne permet de considérer le bruit électronique. Ce modèle, comptant six paramètres libres, est ajusté à des spectres réalisés sur le prototype. L'étude des paramètres extraits caractérise les performances de chaque détecteur dans toutes les configurations de tension et de t peaking et permet d'optimiser les performances de l'instrument
Impacts de l'anthropisation sur la diversité odonatologique au sein des cours d'eau : vers une meilleure prise en compte des espèces de la directive habitats faune flore by Alice S Denis( Book )

2 editions published in 2018 in French and held by 2 WorldCat member libraries worldwide

In a context of global biodiversity crisis, reconciling the development of wealth-generating industry and agriculture with nature conservation is a crucial issue. Economic stakeholders are legally obliged to apply the mitigation hierarchy doctrine and thus "avoid, mitigate, and compensate" for their project's impacts. However, for invertebrate protected species, and particularly dragonfly species, basic knowledge on their ecology and population dynamics is lacking. It is thus difficult to accurately anticipate the impacts and propose efficient avoidance and compensation measures. This is particularly true on rivers, which are ecosystems under high pressure owing to their utility for human beings (e.g. water and food resources, transport, energy production, leisure). The aim of this work is to improve knowledge of three protected riverine species of dragonflies: the Orange-spotted emerald Oxygastra curtisii (Dale, 1834), the Pronged clubtail Gomphus graslinii Rambur, 1842, and the Splendid cruiser Macromia splendens (Pictet, 1843), and to provide better assessment methods to evaluate the impacts of the anthropisation of streams on their populations. We sought in particular (1) to improve environmental impact assessments and management of these species within Natura 2000 sites by proposing a standardised survey protocol, (2) to assess the consequences of habitat change, especially water temperature warming, on their phenology and morphology, and (3) to describe and evaluate the impacts of weirs and hydroelectric dams on their populations. This work took place in the Midi-Pyrénées region in southern France, where populations of these three species are still present. It was carried out in close partnership with the Conservatoire d'Espaces Naturels de Midi-Pyrénées, which coordinates the Regional Action Plan for Odonata, and the Functional Ecology Laboratory EcoLab to ensure direct transfer of the scientific knowledge acquired to the ecosystems managers, economic stakeholders and public authorities responsible for biodiversity conservation
Paléomagnétisme et pétrogenèse des unités paléoprotérozoïques de l'évènement Uatumã au nord du craton amazonien by Paul Yves Jean Antonio( Book )

2 editions published in 2017 in English and held by 2 WorldCat member libraries worldwide

Un volumineux magmatisme anorogénique a recouvert une large partie (1.500.000 km2) du craton Amazonien à 1880 Ma et définit une province magmatique felsique qu'on appelle l'événement Uatumã. L'objectif de ce travail est d'étudier le paléomagnétisme ainsi que la pétrologie de ces roches afin de préciser le cadre spatio-temporel de cet événement et de définir la place du craton Amazonien au sein du Supercontinent Columbia. Deux régions d'études localisées dans le sud-ouest du craton Amazonien (Pará) ont permis de collecter les échantillons nécessaires : (1) la région de Tucumã où 16 filons felsiques, 7 filons mafiques, un filon gabbroïque et 3 sites du socle archéen ont été collectés. (2) la région de São Felix do Xingu où on a échantillonné 7 sites de laves rhyolitiques, 2 sites d'ignimbrites, un filon felsique et un site de brèches volcaniques qui appartiennent à la formation Santa Rosa. 6 sites de la formation Sobreiro (roches volcanoclastiques andésitiques) ainsi qu'un filon felsique de la suite Velho Guilherme ont aussi été collectés. Un des résultats majeurs de la pétrologie des filons felsiques de Tucumã (1880.9 ± 6.7 Ma U-Pb sur zircon) a été de montrer qu'ils représentent le système filonien associé à la formation volcanique Santa Rosa. L'aimantation rémanente des filons felsiques est portée par la magnétite et l'hématite. Cette hématite est syn- à post-magmatique et sa formation, à partir des fluides hydrothermaux, peut être quantifiée grâce certaines propriétés magnétiques. Les désaimantations (en champ alternatif, thermiques) montrent une composante A caractéristique de direction nord-ouest avec une inclinaison positive dont la moyenne par site donne un pôle paléomagnétique localisé à 52.9°S, 76.4°E (A95= 10.4°, K= 13.52). Une réaimantation régionale mésozoïque en relation avec les filons de la CAMP (Central Atlantic Magmatic Province) est observée dans cette région. Les meilleurs résultats paléomagnétiques ont été obtenus dans la région de São Felix de Xingu. Deux nouveaux pôles paléomagnétiques primaires, ont été déterminés: (i) Le pôle SF1 (319.7°E, 24.7°S, N= 10; A95= 16.9°) est obtenu pour des andésites et des rhyolites datés à 1877.4 ± 4.3 Ma (U-Pb zrn, LA-ICPMS), son origine primaire est confirmée par un test de contact inverse (> 1853 Ma). La pétrographie montre que la minéralogie magnétique de cette composante est l'hématite formée par des fluides hydrothermaux syn- à post-magmatiques. (ii) Le pole SF2 (220.1°E, 31.1°N, N= 15; A95= 9.7°) est déterminé par l'aimantation rémanente du filon felsique de la Suite Velho Guilherme, mais aussi par l'aimantation secondaire dans les échantillons de la formation Santa Rosa et Sobreiro. Un âge de 1853.7 ± 6.2 Ma (U-Pb zrn, LA-ICPMS) est calculé pour le filon felsique portant SF2, dont l'origine primaire est confirmée par un test de contact positif. Les pôles SF1 et SF2 sont très différents, malgré une différence d'âge de seulement ~25 Ma. Des résultats paléomagnétiques similaires ont été obtenus pour les pôles de même âge dans d'autres cratons (Inde, Supérieur (Laurentia), Slave (Laurentia), Kalahari, Baltica et Sibérie), et peuvent être expliqués par un événement de Vrai Dérive Polaire (VDP). Cette époque (~1880 Ma) est marquée par une forte activité du manteau, qui aboutit à la formation du Supercontinent Columbia, autour de 1850 - 1800 Ma. La formation de superpanaches est une conséquence possible de l'assemblage du supercontinent et de l'effet d'isolation thermique du manteau qui en résulte, ou bien lui est concomitante. Les superpanaches peuvent provoquer des perturbations de densité modifiant le tenseur inertiel de gravité de la Terre. Un rapide événement de Vrai Dérive Polaire (VDP) peut ainsi avoir eu lieu, ce qui va déplacer rapidement les continents et les superpanaches vers l'équateur. Ces événements peuvent être liés à une réorganisation du manteau dans son ensemble à la suite d'une période de faible activité magmatique entre 2400 et 2200 Ma
Etude de la rétrodiffusion altimétrique pour la caractérisation des surfaces et de l'humidité des sols en Afrique de l'Ouest by Christophe Fatras( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

Le satellite altimétrique interférométrique SWOT, dont le lancement est prévu pour 2020, devrait pour la première fois permettre une couverture globale en quelques jours d'un radar proche-nadir en utilisant la bande de fréquence Ka. Or, l'utilisation d'une telle bande de fréquence est encore mal documentée pour l'hydrologie continentale. En particulier, le contraste du coefficient de rétrodiffusion sur les sols et sur les surfaces en eau pour des angles de visée nadir et proche nadir est une problématique majeure. C'est ce qui fait l'objet de ces travaux de thèse. Dans un premier temps, l'étude de la variation des coefficients de rétrodiffusion en provenance d'altimètres en bandes C et Ku et de diffusiomètres utilisant les mêmes bandes de fréquence sur l'Afrique de l'Ouest a montré qu'il existe un lien quantifiable entre l'humidité du sol et le coefficient de rétrodiffusion. En région semi-aride ce lien se manifeste via une hausse des coefficients de rétrodiffusions durant la saison humide par rapport à la saison sèche. L'analyse avec des données annexes d'humidité du sol et de précipitations a pu également montrer que le radar nadir détecte plus précisément les changements d'humidité du sol par rapport à la diffusiométrie radar à visée latérale. Dans le but de mieux comprendre la rétrodiffusion en bande Ka, très peu documentée, deux campagnes de mesures radar ont été réalisées, l'une sur des surfaces en eau à rugosité contrôlée, l'autre sur un terrain contrôlé en rugosité et humidité du sol. En parallèle, un programme de simulation de la rétrodiffusion altimétrique a été développé pour pouvoir analyser les effets d'un faible nombre de variables sur des sols réalistes, dans le but de simuler les variations du coefficient de rétrodiffusion. Ces mesures et ces simulations ont ensuite pu être comparées aux séries temporelles issues du satellite altimétrique AltiKa, fonctionnant en bande Ka et lancé en février 2013, sur différents sites représentatifs des régions bio-climatiques d'Afrique de l'Ouest. Il en ressort que la bande Ka présente une forte sensibilité aux changements d'humidité du sol. Il est également montré que les coefficients de rétrodiffusion en provenance d'AltiKa sur les sols et sur l'eau peuvent être similaires au nadir
Observation satellitaire et modélisation de l'albédo des forêts sur le territoire français métropolitain : dynamiques temporelles et impacts radiatifs by Carole Planque( Book )

2 editions published in 2018 in French and held by 2 WorldCat member libraries worldwide

The forests impact the climate but their effect is uncertain, in particular in the areas with temperate climate. In temperate forests, biogeochemical and biophysical processes can present either a cooling or a warming effect on climate. A first step to improve the evaluation of the climatic effect of forests is to go forward with the modeling of all biogeochemical and biophysical processes in LSMs ("Land Surface Models") used in the atmospheric models used for numerical weather forecast and climate predictions. Surface albedo is identified as a key variable of the impact of forests in terms of radiative forcing. However, surface albedo is represented in a simplified way in LSMs and is, more often than not, non-evolutive. In this context, the objective of this PhD work is to contribute to the improvement of surface albedo modeling in LSMs. A step forward was to identify the biophysical variables which drive the surface albedo of forests in space and time, using satellite observations. A predictive model of the forest albedo was developed considering the spatial resolution used in LSMs. Mainland France was selected as a study area from 2001 to 2013. It was shown that over this period, 94.4% of the forest area presented a relatively stable seasonal albedo cycle, from one year to another. Among the remaining 5.6%, changes in albedo were induced by sudden changes in the vegetation cover, but also in some forests by an increase in greenness. With the aim of identifying the variables which drive the seasonal variations of the surface albedo of forests, a new method was developed to split satellite-derived surface albedo into soil and vegetation albedo values. Soil albedo showed inter- and intra-annual temporal dynamics which are correlated with top soil moisture. The temporal variability of the average soil albedo can be described by its standard deviation, which is of 0.016. In comparison, the values obtained with preexisting methods range from 0 to 0.004. In addition, the seasonal cycle of soil albedo is consistent with the rainfall regime: the yearly maximum average monthly albedo matches the months with less precipitation. This was the case for 68% of forest pixels, against 32% using surface albedo instead of soil albedo. The median values of the vegetation (soil) albedo were estimated with an uncertainty of 2% (10%). These disaggregated albedo values (soil and vegetation) were used to produce average annual cycles. The latter are used to force the predictive model of the forest albedo which is based on LSMs' simulated variables. The validation was conducted using MODIS satellite-derived surface albedo observations. Average error values of 12% and 8% were obtained in the VIS and the NIR spectral domains, respectively (R of 0.63 in the VIS). This is an improvement with respect to pre-existing methods (R of 0.45 in the VIS). Disaggregating surface albedo showed that the effect of temperate forests on the radiative budget depends on season, forest type and soil type. Over mainland France, 77.3% of the forests present a radiative impact which can lead to a warming effect during the summer. If the increase in greenness detected in some forests were to spread to all French forests, the average radiative impact during the summer could be as large as 0.187± 0.04 W.m-2. The disaggregation method developed during this PhD work is under implementation in the operational chain of the EUMETSAT LSA-SAF service. Thanks to this implementation it could be eventually possible to parameterize disaggregated albedo values in LSMs. This will allow the assimilation of surface albedo observations in LSMs
Characterization of heavy precipitation on Corsica by Phillip Scheffknecht( Book )

2 editions published in 2016 in English and held by 2 WorldCat member libraries worldwide

Heavy precipitation is one of the primal meteorological reasons for property damage, injuries, and deaths. In the framework of the Hydrological Cycle of the Mediterranean (HyMeX) program, heavy precipitation is analyzed throughout the entire Mediterranean basin with a special focus on the northwestern Mediterranean. This work studies in particular the mechanisms of high precipitation events (HPEs) on Corsica. For this purpose, a 31 year (1985 - 2015) climatology of HPEs on Corsica is presented. In addition, three HPEs during autumn 2012 are analyzed in detail using observations and numerical modeling. A climatology of 173 events shows that the eastern half of Corsica, specifically the orography, is most affected by high precipitation events. The months from September to December, most of all October, are identified as most prone to heavy precipitation events over Corsica. A principal component analysis is used to classify the events into three categories, which correspond to warm autumn and cold winter Mediterranean cyclones as well as a mixed category which contains also larger scale Atlantic cyclones. The heaviest precipitation is observed when warm moist southeasterly flow encounters the Corsican orography. In addition, three case studies are presented, each with different mechanisms involved. A stationary cyclone on 4 September 2012 led to widespread precipitation over Corsica with the most intense rain observed over the east of the island, along the coast and the orography. On 31 October, a fast moving cyclone caused a multi-phase event, which was characterized by low level wind turning from southeast to west while precipitation gradually changed from convective along the orography in the east of the island to stratiform mainly over the west and southwest. The last event, 23 October 2012, was comprised of a line convective cells which formed over stationary lee side convergence southeast of Corsica. The convective cells were advected toward the island by the mid- and upper level southeasterly wind. These conditions allowed the convective line to remain stationary, resulting in a highly localized and relatively short event. The findings confirm that the numerical model Meso-NH is well capable of simulating such events with satisfactory precision at a grid spacing of 2.5 km. However, the studies also underline the importance of well captured initial conditions. Additionally, the spatial distribution of precipitation is highly dependent on the representation of the orography in the model as well as the horizontal grid spacing and is improved when using a horizontal grid spacing of 500 m instead
Evaluation de la ressource en eau associée au manteau neigeux sur le Mont Liban à partir d'observations et de la modélisation by Abbas Fayad( Book )

2 editions published in 2017 in English and held by 2 WorldCat member libraries worldwide

Lebanon's water resources are under increasing pressure due to economic development, demographic growth, unsustainable water resource management, and climate change. The Mount- and Anti-Lebanon Mountains are natural water towers for Lebanon as they play an important role in enhancing orographic precipitation. Due to the influence of the Mediterranean climate, most precipitation above 1200 m a.s.l. falls as snow during winter season. As a result, snowmelt is an important contributor to the national water balance. In particular, snowmelt from Mount-Lebanon feeds the karst groundwater systems, which provide key water resources to the coastal region. Despite the importance of the snow cover in the Lebanese mountains, the actual snowpack spatial and temporal variability and its contribution to the spring and river discharges in Lebanon remains poorly constrained. The objective of this work is to reduce this lack of knowledge using a combination of in situ measurements, remote sensing observations and modelling of the snowpack in Mount-Lebanon. 1. We first present an extensive review of the literature about the snow hydrological processes in Mediterranean-like mountain regions. Many studies - mainly from Western USA and Southern Europe mountains - emphasize the strong impact of the interannual Mediterranean climate variability on the snowpack dynamics. The high incoming solar radiation is an important driver of the snowpack energy balance, but the contribution of heat fluxes is stronger at the end of the snow season. Snow sublimation and rapid densification are important processes to consider. Hybrid approaches combining weather station data with optical remote sensing of the snow extent through modelling are recommended to tackle the lack of spatially-distributed observations of the meteorological forcing. 2. Then, we introduce an original dataset on the snow cover in Mount-Lebanon for the period 2013-2016. We collected field observations of the snow height (HS), snow water equivalent (SWE), and snow density between 1300 and 2900 m a.s.l. in the western slope of Mount-Lebanon. In addition, continuous meteorological data were acquired by three automatic weather stations located in the snow dominated region of Mount-Lebanon. The MODIS snow product was used to compute the daily snow cover area in three snow dominated basins. We find that HS and SWE have large variances and that snow density is high. The strong correlation between HS and SWE may be useful to reduce the amount of field work for future operational monitoring. 3. Using these data we set up a distributed snowpack energy balance in the Mount- Lebanon at 100 m resolution. The model is validated at different scales using the observed SWE, snow density, HS and SCA. A simulation with very limited adjustments to the default parameterization is found to correctly capture most of the observations. This simulation allows the estimation of the SWE evolution and snow melt in the three study basins between 2013 and 2016. This research highlighted the importance of conducting simultaneous field surveys and meteorological observations to gain insights into the physical processes driving snowpack evolution in Mount-Lebanon. Finally, the influence of snow erosion by wind and the influence of dust deposits on snowmelt, remains less known, and are warrant for future research
Apport des données multispectrales (hyperfréquences, thermique, optique) pour le suivi hydrique des cultures : application aux couverts de blé et de tournesol by Benoît Cheul( Book )

2 editions published in 2019 in French and held by 2 WorldCat member libraries worldwide

The south-west of France has been identified as a region for which climate change effects will be the harder to mitigate. Agriculture is already representing 41% of the water use in the Adour-Garonne watershed and will have to adapt to the effects of climate change on the water cycle: more irregular precipitations, lowering of the rivers rate of flow... New methods for monitoring will be necessary for the responsible use of water. Loss to the atmosphere is the major constraint of the water budget in agricultural areas. This evapotranspiration flux is part of the coupled water and energy budget of the surface; in particular, it allows one to identify water stress events. The estimation of evapotranspiration flux at a large scale relies on remote sensing images or a modeling of exchanges at the surface, sometime both. The wavelength domains used allow sampling of different surface properties. Microwave used in radar is sensitive to the target geometry and its water content. It is also insensitive to cloud cover. Visible images are used to monitor vegetation development with spectral indexes. Thermal infrared gives information of surface temperature and can detect water stress. The combined use of these three wavelength domains, each with its respective strength, in a water and energy budget modeling scheme could allow to better monitor surface processes. This study focuses on the complementarities of the three wavelength domains in a case of wheat and sunflower monitoring in south west of France over the year 2010. It is focused on the spatial and temporal variability of a visible based vegetation descriptor (the GAI: Green Area Index), surface temperature (Ts) and C-band backscattering coefficient over 13 fields of wheat and 6 fields of sunflower. This variability allows us to select various parameterizations of the water and energy budget model SEtHyS. The study is organized as follow: - We first studied the sensitivity of C-band backscattering coefficient to the spatial and temporal variability of 2 surface properties: top soil moisture and GAI. The 4 radar polarizations as well as 2 polarization ratios are covered. - We adapted the [surface temperature-vegetation index] method for a temporal use of the entire remote sensing dataset. Using this method we retrieved an index we called RTVDI (Relative Temperature Vegetation Difference Index) which we used to rank fields and extract patterns. - We finally used the SEtHyS model to try and reproduce the RTVDI variability previously observed. The first approach is realized using the model in direct mode to identify sensitive parameters for water budget modeling. The radar sensitivity study confirmed the vegetation monitoring ability of C-band radar. Thresholds on height allowed identifying periods when radar is sensitive to top soil moisture. The modified trapezoid method allowed selecting groups of fields with variable hydric properties.[...]
Analyse des effets directionnels dans l'infrarouge thermique dans le cas des couverts végétaux continus : modélisation et application à la correction des données spatiales by Clément Duffour( Book )

2 editions published in 2016 in French and held by 2 WorldCat member libraries worldwide

Remotely-sensed data in thermal infrared (TIR) are an essential source of information to estimate surface fluxes and to monitor the functioning of agro-ecosystems. However, surface temperature measurements are prone to directional effects ('hot spot' phenomenon)which may result in an error up to 10°C. They have to be taken into account in the framework of operational applications. The work proposed here aims at modelling the directional anisotropy of continuous vegetated canopies in order to develop operational methods for correcting land surface temperature measurements carried out by TIR satellites. This work is mainly motivated by the CNES projects aiming at developing a new TIR spatial mission combining both high spatial resolution and high revisit time capacities. Two steps were carried out. The first is based on the use of the deterministic SVAT model SCOPE (Soil Canopy Observation, Photochemistry and Energy fluxes), able to simulate directional radiances at top of canopy in both optical and TIR domains. In this thesis, it is validated against experimental measurements and its ability to successfully simulate TIR directional anisotropy demonstrated. Then it is used to study the sensitivity of anisotropy to canopy structure, water status of soil and vegetation, meteorological forcing and solar and observer angular configurations. The consequences of the combined features of satellites orbits, geographical position of the scanned sites and acquisition date on anisotropy are discussed. In the second part, we propose a simplified parametric model (called 'RL'). SCOPE is used as a data generator. The RL model is deemed suitable and able to correctly reproduce directional signatures both in terms of geometry (hot spot position) and amplitude of these effects. A comparison with the only one parametric model previously used in TIR remote sensing (Vinnikov's approach) confirms the good capacities of the RL model. The RL model is thus a potential candidate to the future satellite processing chains
Representing past and future hydro-climatic variability over multi-decadal periods in poorly-gauged regions : the case of Ecuador by Bolivar Erazo( Book )

2 editions published in 2020 in English and held by 2 WorldCat member libraries worldwide

This thesis investigates methods to represent the past and future hydro-climatic variability in space and over time in poorly-gauged regions. It proposes a complete and reproducible procedure applied to the continental Ecuador to deal with observed and simulated hydro-climatic data in order to represent past variability and project the potential impact of climate change on water resources by the end of the 21st century. Up-to-date techniques were identified in a literature review and were integrated in a chain protocol to obtain continuous space-time series of air temperature, precipitation and streamflow over past and future multi-decadal periods. Three central chapters are dedicated to this objective according to the following topics: (1) regionalization of air temperature and precipitation from in situ measurements by comparing deterministic and geostatistical techniques including orographic corrections; (2) streamflow reconstruction in various catchments using conceptual hydrological models in a multi-model, multi-parameter approach; and (3) hydro-climate projections using climate model simulations under a high range emission scenario. Climate regionalization revealed the importance of calibrating parameters and of assessing interpolated fields against independent gauges and via hydrological sensitivity analyses. Streamflow reconstruction was possible with the regionalized climate inputs and the combined simulations of three hydrological models evaluated in contrasting climate conditions. Future medium term (2040-2070) and long term (2070-2100) hydro-climatic changes were analysed with confidence intervals of 95% using scenarios from nine climate models and transferring the model parameters calibrated for streamflow reconstruction. Analysis of hydro-climatic variability over the period 1985-2015 showed a slight increase in temperature, while precipitation variability was linked to the main modes of El Niño and La Niña phases at inter-annual scale and to the displacement of the inter-tropical convergence zone (ITCZ) at seasonal scale. Under climate change, a general increase in temperature (+4.4 °C) and precipitation (+17%) is expected by the end of the 21st century, which could lead to between +5% and 71% increase in mean annual streamflow depending on the catchments. These results are discussed in terms of significance for water management before suggesting future hydrological research such as regionalizing streamflow, better quantifying uncertainties and assessing the capacity to meet future water requirements
Structure verticale des tourbillons de mésoéchelle dans les quatre grands systèmes d'upwelling de bord est by Cori Pegliasco( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

Merging ~10 years of altimetry maps and vertical profiles provided by Argo floats, we aim to study in details the eddy's surface characteristics and vertical structure in the 4 major Eastern Boundary Upwelling Systems (EBUS : Peru-Chile, California, Canaries and Benguela), sharing similar large-scale dynamics. Our main results show that the eddies detected on altimetry maps in the 4 EBUS have close physical properties, with a lot of small-scale structures (radius < 40km, amplitude < 1cm and lifetime < 30 days). In contrast, the few eddies sampled by Argo floats have larger dimensions (radius of ~90-140 km, amplitude of ~3-7 cm) and longer lifetimes (6-10 months). The major bias with the analyzed vertical structure is the over representation of these large-scale eddies. The temperature and salinity anomaly mean profiles acquired by Argo floats surfacing within eddies reveals a strong heterogeneity between each of the 4 EBUS, but also within them. The eddies' vertical structure is strongly influence by the local hydrology and dynamics. For example, the subsurface-intensified eddies of the PCUS tend to be located in the Southern part of this EBUS, while the surface-intensified eddies are preferentially located near the Northern boundary of the subtropical gyre. In the CALUS, we can identify Cuddies in some coastal sub-regions, but in this EBUS, most of the eddies are intensified at the base of the pycnocline, with a reversal of the salinity anomaly compared to the surface layers. In the CANUS, the Cape Verde frontal zone separates distinct subsurface-intensified eddies and some Meddies in the North, from the Southern part, where eddies are surface-intensified. In the same way, the Angola-Benguela Front of the BENUS separates the surface-intensified eddies in the North from strong, deep-reaching anomalies in the South. The Southern-most part of the BENUS is also a preferential pathway for the large Agulhas Rings and their associated cyclones. The respective contributions of isopycnal advection and vertical displacement improve the description of these very diverse structures. The presence of several eddy-types, with distinct thermohaline properties (surface or subsurface-intensified, deep vertical extend, intense or not, etc.) is confirmed by the study of eddies generated in the coastal area of each EBUS. Their Lagrangian analysis allows us to describe the temporal evolution of their vertical structure, which shows an unexpected temporal homogeneity. This manuscript presents different efficient tools used to analyze the surface characteristics, the thermohaline properties and the temporal evolution of mesoscale eddies in the 4 major EBUS, highlighting their diversity
 
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