Les impacts géomorphologiques de la déglaciation dans la région du Skagafjörður (Islande septentrionale)

Located north of Iceland, the Skagafjörður area has experienced an ice shrinking during the Late Weichselian deglaciation.This period of transition from glacial to non-glacial conditions was characterized by significant impacts on reliefs and slope dynamics. The slope instabilities induced by the deglaciation operate in the form of: (i) slope deformations (i.e. gravitational spreading) and (ii) slope failures (i.e. mass-movements). This thesis is devoted to these slope readjustments which occurred in context of deglaciation. Accordingly, the thesis is related to the paraglacial geomorphology which focuses on “non glacial earth surface processes, sediment accumulations, landforms, landsystems and landscapes that are directly conditioned by glaciation and deglaciation” (Ballantyne, 2002). Two major uncertainties remains about: (i) the relationship between slopeinstabilities, both in the form of gravitational spreading and mass-movement, and the sequence of deglaciation, and (ii)the influence of paraglacial slope instabilities in the shaping of the erosional landforms usually attributed to the action ofglacial erosion processes (i.e. cirques and troughs). Main results carried out during this research highlight: (i) asignificant influence of paraglacial gravitational spreading and mass-movement respectively in the carving of troughsand cirques and (ii) a potential influence of gravitational spreading as a precursor of mass-movement, throughoutthe progressive degradation of slope stability induced by the gravitational deformation which may ultimately result inrock-slope failures.Située au nord de l’Islande, la région littorale du Skagafjörður a connu, au cours de la déglaciation du Weichsélien Tardif, une fonte massive des édifices glaciaires. Cette période de déglaciation a eu des impacts importants sur les reliefs et les dynamiques de versant. Les instabilités qui ont affecté les versants au cours de cette séquence s’expriment selon deux modalités principales : (i) les réajustements par déformation (i.e. les étalements gravitaires) et (ii) les réajustements par glissement (i.e. les mouvements de masse). C’est à l’étude de ces réajustements de versants qui opèrent en contexte de déglaciation qu’est consacrée cette thèse. A ce titre, elle s’inscrit dans le cadre de la géomorphologie paraglaciaire qui a pour objet les « processus de surface, formations, formes et géosystèmes qui sont directement conditionnés par la glaciation et la déglaciation » (Ballantyne, 2002). Ces réajustements paraglaciaires de versant sont abordés autour de deux questions : (i) le rôle de la déglaciation dans la mise en place des réajustements de versants et (ii) le rôle des réajustements de versantsdans le façonnement des auges et des cirques glaciaires. Les résultats des recherches réalisés dans le cadre de cette thèse font apparaître : (i) une influence significative des instabilités paraglaciaires de versant (i.e mouvements de masse et étalements gravitaires) dans le façonnement et l’érosion des reliefs des milieux froids et (ii) un rôle potentielde la dynamique d’étalement gravitaire dans la dégradation progressive de la stabilité des pentes en contexte de déglaciation qui conduit, in fine, au déclenchement des mouvements de masse

Guiding Active Contours for Tree Leaf Segmentation and Identification

International audienceIn the process of tree identi cation from pictures of leaves in a natural background, retrieving an accurate contour is a challenging and crucial issue. In this paper we introduce a method designed to deal with the obstacles raised by such complex images, for simple and lobed tree leaves. A rst segmentation step based on a light polygonal leaf model is first performed, and later used to guide the evolution of an active contour. Combining global shape descriptors given by the polygonal model with local curvature-based features, the leaves are then classi ed over nearly 50 tree species

A Model-Based Approach for Compound Leaves Understanding and Identification

International audienceIn this paper, we propose a specific method for the identification of compound-leaved tree species, with the aim of integrating it in an educational smartphone application. Our work is based on dedicated shape models for compound leaves, designed to estimate the number and shape of leaflets. A deformable template approach is used to fit these models and produce a high-level interpretation of the image content. The resulting models are later used for the segmentation of leaves in both plain and natural background images, by the use of multiple region-based active contours. Combined with other botany-inspired descriptors accounting for the morphological properties of the leaves, we propose a classification method that makes a semantic interpretation possible. Results are presented over a set of more than 1000 images from 17 European tree species, and an integration in the existing mobile application Folia is considered

Understanding Leaves in Natural Images - A Model-Based Approach for Tree Species Identification

International audienceWith the aim of elaborating a mobile application, accessible to anyone and with educational purposes, we present a method for tree species identification that relies on dedicated algorithms and explicit botany-inspired descriptors. Focusing on the analysis of leaves, we developed a working process to help recognize species, starting from a picture of a leaf in a complex natural background. A two-step active contour segmentation algorithm based on a polygonal leaf model processes the image to retrieve the contour of the leaf. Features we use afterwards are high-level geometrical descriptors that make a semantic interpretation possible, and prove to achieve better performance than more generic and statistical shape descriptors alone. We present the results, both in terms of segmentation and classification, considering a database of 50 European broad-leaved tree species, and an implementation of the system is available in the iPhone application Folia

Précision du monitorage non invasif de l'hemoglobinémie par oxymétrie pulsée chez les patients admis en réanimation pour hemorragie digestive grave

BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

A paraglacial rock-slope failure origin for cirques: a case study from Northern Iceland

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Is gravitational spreading a precursor for the Stífluhólar landslide (Skagafjörður, Northern Iceland)?

International audienceIn Iceland, the Late Weichselian deglaciation led to paraglacial topographic readjustments in the form of extensivedeep-seated gravitational slope deformation (DSGSD) and large rockslope failures (landslides and rock-avalanches).Here we provide age estimates for the Stí" uhólar landslide (Tröllaskagi Peninsula, Northern Central Iceland),which indicate that this occurred between the end of the Late Weichselian deglaciation (15-13 ka cal. yr. BP) and8200 ± 1400 cal. yr. BP. Our surface observations also suggest that the Stífluhólar landslide was probably initiatedby propagation and connection of DSGSD failure planes. This observation suggests that the DSGSD can act as aprecursor for landsliding in paraglacial settings. However, further investigations are still required to fully assess therole of DSGSD as a landslide precursor, both at the local and at a regional scale. Comparisons with other examplesof paraglacial rock slope failures in Northern Iceland and in the world suggest that DSGSD is not the main orsuficient precondition for large landslides. The landslide of Stífluhólar occurred due to some combination offavorable preconditioning, predisposing and triggering controls. Predisposing controls include: the favourable dipof the bedding planes in the basaltic bedrock and the presence of intercalated poorly cohesive layers of palagonitebetween the lava layers, probably acting as basal sliding planes for the landslide

Gravitational spreading of mountain ridges coeval with Late Weichselian deglaciation: impact on glacial landscapes in Tröllaskagi, Northern Iceland

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Guiding Active Contours for Tree Leaf Segmentation and Identification

International audienceIn the process of tree identi cation from pictures of leaves in a natural background, retrieving an accurate contour is a challenging and crucial issue. In this paper we introduce a method designed to deal with the obstacles raised by such complex images, for simple and lobed tree leaves. A rst segmentation step based on a light polygonal leaf model is first performed, and later used to guide the evolution of an active contour. Combining global shape descriptors given by the polygonal model with local curvature-based features, the leaves are then classi ed over nearly 50 tree species