Monitoring of Tectonic Deformation by Mining Satellite Image Time Series

National audienceCet article présente une nouvelle approche pour l'analyse de séries d'images satellite InSAR (Interferometric Synthetic Aperture Radar) et son application au monitoring de fluage le long d'une faille sismique active majeure. Les données InSAR permettent de mesurer les déformations du sol entre deux dates sur de grandes zones géographiques, mais la précision des mesures reste limitée par le bruit du aux variations en temps et en espace des conditions atmosphériques. L'approche proposée combine des techniques d'analyse d'images satellite et des techniques de fouille de données. Elle permet de traiter des séries d'images satellite InSAR de façon non supervisée, même avec des conditions atmosphériques variables, et fournit aux experts des cartes d'évolutions décrivant les déformations du sol. Des résultats expérimentaux sur une série d'images ENVISAT de la faille de Haiyuan (zone Nord-Est du plateau tibétain) sont présentés. Les cartes obtenues montrent un glissement asismique continu superficiel le long d'une portion de la faille, ce qui est consistant avec les modèles géophysiques actuels

Phase separation in model colloidal liquids by Brownian dynamics simulations.

The technique of Brownian Dynamics simulation has been used to follow the evolution of model colloidal systems during phase separation in the liquid-vapour and solid-vapour regions of the phase diagram. Systems of monodisperse spherical particles interacting via LJ m:n type potentials were quenched in temperature from the one-phase region into the two phase region. Various structural and rheological properties were followed as the systems evolved, including the radial distribution functions, the small angle scattering peak of the structure factor, the interaction energy and the linear response rheology. The scaling behaviour of these quantities was found to be similar to that observed in light scattering experiments following the phase separation of colloidal systems. The aggregate structure could not be represented well by a single fractal dimension. Some evidence of fractal structure was found early in the phase separation, however the reversibility of the interactions allowed for a high degree of restructuring which led to a collapse of the initially tenuous structure into dense aggregates. The local structure was sensitive to the range of the interaction potential - as the potential became more short-ranged, increasing evidence of crystallisation of the denser phase was apparent from the form of g(f). Particles with 12:6 interactions formed structures displaying the rheological strength associated with an elastic gel. However restructuring was continual, resulting in a dense compact structure. The short-range 36:18 potential retained a tenuous gel-like structure and displayed an arrest of phase separation on long lengthscales. However, the particles did not have the interaction strength necessary to give significant rigidity to the system. This suggests that to form an arrested state with elastic gel-like rheology it would be necessary to have a more permanent form of interaction, in addition to the short-range reversible interactions used in this work

Phase separation in model colloidal liquids by Brownian dynamics simulations.

The technique of Brownian Dynamics simulation has been used to follow the evolution of model colloidal systems during phase separation in the liquid-vapour and solid-vapour regions of the phase diagram. Systems of monodisperse spherical particles interacting via LJ m:n type potentials were quenched in temperature from the one-phase region into the two phase region. Various structural and rheological properties were followed as the systems evolved, including the radial distribution functions, the small angle scattering peak of the structure factor, the interaction energy and the linear response rheology. The scaling behaviour of these quantities was found to be similar to that observed in light scattering experiments following the phase separation of colloidal systems. The aggregate structure could not be represented well by a single fractal dimension. Some evidence of fractal structure was found early in the phase separation, however the reversibility of the interactions allowed for a high degree of restructuring which led to a collapse of the initially tenuous structure into dense aggregates. The local structure was sensitive to the range of the interaction potential - as the potential became more short-ranged, increasing evidence of crystallisation of the denser phase was apparent from the form of g(f). Particles with 12:6 interactions formed structures displaying the rheological strength associated with an elastic gel. However restructuring was continual, resulting in a dense compact structure. The short-range 36:18 potential retained a tenuous gel-like structure and displayed an arrest of phase separation on long lengthscales. However, the particles did not have the interaction strength necessary to give significant rigidity to the system. This suggests that to form an arrested state with elastic gel-like rheology it would be necessary to have a more permanent form of interaction, in addition to the short-range reversible interactions used in this work

Fouille de données spatio-temporelles appliquée aux séries d'images satellite

National audiencePas de résum

Fouille de données spatio-temporelles appliquée aux séries d'images satellite

National audiencePas de résum

Fouille de données spatio-temporelles appliquée aux séries d'images satellite

National audiencePas de résum

Iterative Summarization of Satellite Image Time Series

International audienc

Iterative Summarization of Satellite Image Time Series

International audienc