Hierarchical Segmentation of Polarimetric SAR Images Using Heterogeneous Clutter Models

International audienceIn this paper, heterogeneous clutter models are used to describe polarimetric synthetic aperture radar (PolSAR) data. The KummerU distribution is introduced to model the PolSAR clutter. Then, a detailed analysis is carried out to evaluate the potential of this new multivariate distribution. It is implemented in a hierarchical maximum likelihood segmentation algorithm. The segmentation results are shown on both synthetic and high-resolution PolSAR data at the X- and L-bands. Finally, some methods are examined to determine automatically the "optimal" number of segments in the final partition

Integrating electromagnetic and hydrodynamic models for the characterization of radar targets in marine environment

The paper describes a simulation methodology for radar targets in marine environment. Our approach is based on a new model, called "Scattering Center Set Unified Representation", which is able to approximate the backscattered radar target echo for any aspect angle. This model is fast to calculate and has the advantage to take into account the partial or total target concealing due to the sea waves. It associates to any target aspect a scattering center set. An amplitude map accounts for each scattering center anisotropy and geometrical visibility. A virtual model is then used for describing the target motion and its concealing by the sea waves. The influence of the sea clutter is also taken into account. The radar signatures used in our simulations have been measured in the anechoic chamber of ENSIETA for four scale-reduced naval targets. The paper also presents some imagery and classification results, which are aimed to illustrate the other side of the naval target characterization problem.L'article présente une méthodologie de simulation d'échos de cibles radar en environnement marin. La procédure est basée sur un nouveau modèle, appelé « Ensemble de Points Brillants en Représentation Unifiée » (EPB-RU), qui permet d'approcher le signal écho d'une cible radar pour l'ensemble de ses orientations. Ce modèle est rapide à calculer et a l'avantage de prendre en compte le masquage partiel ou total de la cible par les vagues de la mer. Il associe à chaque orientation de la cible un ensemble de points brillants (EPB). Pour chaque point brillant du modèle, une carte d'amplitude prend en compte son anisotropie et sa visibilité en fonction de l'angle de visée. Un modèle virtuel combiné mer-navire est utilisé pour décrire le mouvement de la cible et le masquage introduit par les vagues de la mer. L'influence du fouillis de mer est également prise en compte. Les signatures radar utilisées dans nos simulations correspondent à quatre maquettes de cibles navales mesurées dans la chambre anéchoïde de l'ENSIETA. L'article présente aussi quelques résultats d'imagerie radar et de classification, qui illustrent l'aspect inverse du problème de la caractérisation des cibles navales dans leur environnement

Advanced Sea Clutter Models and their Usefulness for Target Detection

International audienceRobust naval target detection is of significant importance to national security, to navigation safety, and to environmental monitoring. Here we consider the particular case of high resolution coastal radars, working at low grazing angles. The robustness of detection heavily relies on the appropriate knowledge of two classes of backscattered signals: the target echo, and the sea echo. The latter, usually regarded as a noise, is known as the sea clutter. This particular combination, of high resolution and low grazing angles, raises considerable challenges to radar processing algorithms. Specifically, the probability density function governing the sea clutter amplitude is no more Gaussian and a lot of effort has been aimed at characterizing it. Three approaches are reviewed here: the stochastic, texture and chaotic models. While the stochastic models represent an essay to extend classical detection theory to radars operating in marine environment, the other two models represent entirely new paradigms. Since each model has its strengths and weaknesses and more testing on real data is required to credibly validate any of the proposed models, a definitive conclusion is far from reach. However, critical comments, as well as experimentally supported conclusions are presented in the paper

Superresolution Algorithms for Spatial Extended Scattering Centers

International audienceScattering centers model (SCM) is usually considered for modeling target backscattered signal in high-resolution radar. In this case the impulse response of each scattering center is represented by a time-delayed Dirac pulse. Some of most popular superresolution imagery techniques, such as MUSIC or ESPRIT, are well-matched to this model. Under this hypothesis, they outperform Fourier-based techniques in terms of both spatial and dynamic resolutions. However, the behavior of real-world targets is often very different from that of the SCM. Indeed, their reflectivity function is not confined just to several perfectly localized scattering centers, but it can be rather approximated by a set of scattering regions having different spatial extent. SCM becomes then inappropriate and the superresolution methods may provide unexpected results. Furthermore, the amplitude information is difficult to interpret in this case. In this paper we propose an extension of two superresolution methods, MUSIC and ESPRIT, to cope with extended scattering centers (ESC). According to this model, the impulse response of an ESC is not a Dirac pulse, but a window of finite support. Besides the position, the size (spatial extent) of this window is also recovered. This additional information about the target structure can be used for increasing ATR (automatic target recognition) accuracy and robustness

Modèles statistiques complexes dans le contexte de l'imagerie SAR polarimétrique

National audiencePolarimetry extends the dimensionality of SAR data (to 3 or 4), so the necessity to have multivariate statistic (and non-Gaussian, because of the high resolution) distributions as models for PolSAR data: such are the SIRV (Spherically Invariant Random Vectors). However, as the statistic model becomes so complicated, correctly estimating its parameters gets difficult. More, although they are versatile, the SIRV models are not guaranteed to match the PolSAR data. To evaluate the pertinence of those models with respect to the PolSAR data, through one of their most important statistic property, namely the circularity, it is the purpose of this paper

Multi-Target Tracking Via High-Order Moment Analysis

International audienc

Current Economic and Financial Crisis – New Issues or Returning to the Old Problems? Paradigms, Causes, Effects and Solutions Adopted

At the ideological level, the current crisis, as the others in history, has triggered an intellectual debate among several applicable ideas: ultra-liberal theory of the "invisible hand" of Adam Smith, Keynes's theory of state interventionism and even neo-Marxist theories. Globalization, with all its core components, generates a chain reaction when the phenomenon occurs, either positive or negative. The origin of the current financial crisis should be sought in the effects of massive cross-border capital flows and the use of more complex derivatives. Reaching the saturation of the three engines of economic growth worldwide in the period after the collapse of the socialist bloc is another important cause of all the failures that currently exist worldwide. Acquisition of toxic assets from bank balance sheets, their recapitalization and takeover by the state, but also the reinforcement of the prudential supervision of capitalization, liquidity and risk management system, improved transparency and speed the process of evaluating or reinforcing authorities' response to risk, can be considered short or long term anti-crisis measures, as appropriate

Current Economic and Financial Crisis – New Issues or Returning to the Old Problems? Paradigms, Causes, Effects and Solutions Adopted

At the ideological level, the current crisis, as the others in history, has triggered an intellectual debate among several applicable ideas: ultra-liberal theory of the "invisible hand" of Adam Smith, Keynes’s theory of state interventionism and even neo-Marxist theories. Globalization, with all its core components, generates a chain reaction when the phenomenon occurs, either positive or negative. The origin of the current financial crisis should be sought in the effects of massive cross-border capital flows and the use of more complex derivatives. Reaching the saturation of the three engines of economic growth worldwide in the period after the collapse of the socialist bloc is another important cause of all the failures that currently exist worldwide. Acquisition of toxic assets from bank balance sheets, their recapitalization and takeover by the state, but also the reinforcement of the prudential supervision of capitalization, liquidity and risk management system, improved transparency and speed the process of evaluating or reinforcing authorities’ response to risk, can be considered short or long term anti-crisis measures, as appropriate

Intégration des modèles électroniques et hydrodynamiques pour la caractérisation des cibles radar en environnement marin

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Some Radar Imagery Results Using Superresolution Techniques

International audienc