Simulation on large scale of acoustic signals for array processing

International audienceDue to operational constraints for underwater data acquisition, simulating realistic sonar data, like images, swath bathymetry profiles or interferometric signals, is crucial for tuning detection and classification algorithms according to sensors settings, sea-bottom nature and topography. Moreover, the robustness of any performance estimation or prediction can be greatly enhanced, as soon as such a simulation tool provides a modular and flexible underwater world representation (multiple sensors, environments and acquisition conditions). For signal and array processing, it is essential not only to generate the signal energy backscattered by a resolution cell, but also to produce a phase information that conveys its theoretical statistical properties. To this end, this paper proposes a Brownian motion-based approach to generate complex Gaussian signals from the contribution of a set of extended single scatterers inside a resolution cell. The resulting process preserves the conservation of energy when integrating on surfaces, as well as the decorrelation between different areas of the sea bottom, and the right interference between two sensors for interferometric applications

Super-resolution-based snake model—an unsupervised method for large-scale building extraction using airborne LiDAR Data and optical image

Automatic extraction of buildings in urban and residential scenes has become a subject of growing interest in the domain of photogrammetry and remote sensing, particularly since the mid-1990s. Active contour model, colloquially known as snake model, has been studied to extract buildings from aerial and satellite imagery. However, this task is still very challenging due to the complexity of building size, shape, and its surrounding environment. This complexity leads to a major obstacle for carrying out a reliable large-scale building extraction, since the involved prior information and assumptions on building such as shape, size, and color cannot be generalized over large areas. This paper presents an efficient snake model to overcome such a challenge, called Super-Resolution-based Snake Model (SRSM). The SRSM operates on high-resolution Light Detection and Ranging (LiDAR)-based elevation images—called z-images—generated by a super-resolution process applied to LiDAR data. The involved balloon force model is also improved to shrink or inflate adaptively, instead of inflating continuously. This method is applicable for a large scale such as city scale and even larger, while having a high level of automation and not requiring any prior knowledge nor training data from the urban scenes (hence unsupervised). It achieves high overall accuracy when tested on various datasets. For instance, the proposed SRSM yields an average area-based Quality of 86.57% and object-based Quality of 81.60% on the ISPRS Vaihingen benchmark datasets. Compared to other methods using this benchmark dataset, this level of accuracy is highly desirable even for a supervised method. Similarly desirable outcomes are obtained when carrying out the proposed SRSM on the whole City of Quebec (total area of 656 km2), yielding an area-based Quality of 62.37% and an object-based Quality of 63.21%

Robust Building-based Registration of Airborne LiDAR Data and Optical Imagery on Urban Scenes

The motivation of this paper is to address the problem of registering airborne LiDAR data and optical aerial or satellite imagery acquired from different platforms, at different times, with different points of view and levels of detail. In this paper, we present a robust registration method based on building regions, which are extracted from optical images using mean shift segmentation, and from LiDAR data using a 3D point cloud filtering process. The matching of the extracted building segments is then carried out using Graph Transformation Matching (GTM) which allows to determine a common pattern of relative positions of segment centers. Thanks to this registration, the relative shifts between the data sets are significantly reduced, which enables a subsequent fine registration and a resulting high-quality data fusion

Forward looking sonar data simulation through tube tracing

International audienceSimulating realistic sonar data is crucial for tuning detection and classification algorithms according to environment and acquisition characteristics. Moreover, robustness of performances estimation and prediction applications can be greatly enhanced as soon as such a simulation tool provides both a modular underwater world representation (multiple sensors, environments and acquisition conditions) and a selection of several computational engines (ray theory, parabolic equation, ...). Therefore, we developed such a framework for simulators, allowing both scene design and computational engine choice. Within it, two engines (one for rays, one for tubes) has been successfully implemented and realistic simulations obtained, as shown in the presented simulated sonar images. This paper introduces the simulation of a new imaging sensor (DIDSON acoustic camera) showing the extensibility of the proposed framework while providing realistic and specific front-looking simulated images. Moreover, in order to bypass the scene resolution given by the facet sizes, some georeferenced perturbations are introduced in order to model sub-facet behaviors and produce more realistic responses from the scene with micro and macro textures on the output images

Interferometric signal sonar data simulation through tube tracing

International audienceSimulating realistic sonar data is crucial for tuning detection and classification algorithms according to environment and acquisition characteristics. Moreover, robustness of performances estimation and prediction applications can be greatly enhanced as soon as such a simulation tool provides both a modular underwater world representation (multiple sensors, environments and acquisition conditions) and a selection of several computational engines (ray theory, parabolic equation ...). Therefore, we developed such a framework for simulators, allowing both scene design and computational engine choice. Within it, two engines (one for rays, one for tubes) has been successfully implemented and realistic simulations obtained, as shown in the presented simulated sonar images. Moreover, a first attempt in simulating interferometric signals has also been carried out introducing extended scatterers in order to integrate phenomena like sensor decorrelation

Potential of underwater sonar systems for port infrastructure inspection

International audienceDue to their involvement in several development areas (economy, industry, tourism, etc.) the maintenance and control of port infrastructure is of prime interest. Currently, quay inspection is carried out by divers using underwater cameras. Besides being time consuming, this approach displays several drawbacks: high cost, divers insecurity and lack of precision mainly due to a lack of visibility in turbid water. Therefore, new innovative methods are required to overcome these limitations. Sonar technology is a suitable alternative for quay inspection. It is a rapid and safe way to detect various defects in quay. It provides acoustic image whose quality is much higher than that of images supplied by optical means. The capability and performances of these acoustic systems still remain to be assessed. This is the focus of the proposed research work that will be addressed in this paper. The main purpose is to design and develop a method that will enable the detection and characterization of quay defects using acoustic images

Sonar data simulation & performance assessment through tube ray tracing

International audienceSimulating realistic sonar data is crucial for tuning detection and classification algorithms according to environment and acquisition characteristics. Moreover, robustness of performances estimation and prediction applications can be greatly enhanced as soon as such a simulation tool provides both a modular underwater world representation (multiple sensors, environments and acquisition conditions) and a selection of several computational engines (ray theory, parabolic equation ). Therefore, we developed such a framework for simulators, allowing both scene design and computational engine choice. Within it, a tube engine has been successfully implemented and realistic simulations obtained. Moreover, the engine keeps track of the full propagation history of the simulated acoustic wave allowing mission planning & debriefing to take benefit from this knowledge for environment assessment applications (mine hunting, for instance). Indeed, sea bottom regions non-observed during a survey (either planned or performed) can be computed, outlining areas of potential threats, for instance. Thus, bringing that non-statistical information to CAD/CAC systems may enhance the reliability of their outputs

Underwater environment restitution through sonar images and swath bathymetry rendering

International audienceAccurately simulating sonar images and swath bathymetry profiles enables to render the reality of the underwater environment. This approach is strongly motivated by the operational constraints for data acquisition. Such a tool is especially attractive for tuning algorithms (i.e. detection and classification ones) according to sensors settings and sea-bottom nature and relief. Therefore, we developed such a simulator relying on acoustical ray tracing techniques tailored for considering specific underwater propagation properties (multi-path sound propagation, sound velocity profiles, adaptive ray oversampling to modelize acoustic lobe configuration). It aims at rendering data similar to what real sensors provide in a natural contest. In the proposed approach, the virtual environment gathers both static and dynamic behaviours, namely simulator inputs may be a priori known or updated all along time. Sea-ground truth is provided by either a real elevation map or fractal simulation allowing a fine macro-relief description (flat, rocky patch, rippled sea-bottom). In addition, micro-relief is modelled through sea-bed textures resulting from adequate spatial layouts of ground resolution cells. Sets of natural or manufactured bottom-laying items may be introduced using mesh descriptions (ship wreck, ...) or structured geometric primitives (anchors, pipelines...). Furthermore, the material of the previous inputs tunes their acoustic response. Taking into account carrier trajectory and attitude along time warrants multi-sensor realistic outputs. A great interest of our parallel and modular implementation is an easier incorporation in a more global rendering system. However, its interface proposes real time visualisation of the acquired environment through windows showing current sonar images, swath bathymetry, vehicle attitude and trajectory. Given this flexibility, a promising 3D sea-bottom and objects reconstruction method already benefit from this simulator virtual reality

Sonars cartographiques et interférométrie associée

National audienceL'interférométrie est une technique qui prend une place de plus en plus importante dans les applications sonars et en particulier pour les sonars cartographiques. Ceci s'explique par la simplicité de mise en ?uvre de cette technique et le gain de précision qu'elle apporte. Cet article propose d'analyser les fonctionnements de différents types de sonars cartographiques, en particulier les sonars latéraux et multifaisceaux. Dans un premier temps sont analysés les fonctionnements spécifiques de ceux-ci, en mode classique puis en mode interférométrique. Si cette technique s'adapte très bien à ces appareils de télédétection, le traitement des données nécessite quelques précautions avant de pouvoir reconstruire de manière tridimensionnelle, l'environnement du fond sous marin. Ces précautions concernent les hypothèses de base à respecter ainsi que la prise en considération de l'impact du bruit sur la qualité de la phase interférométrique. En définitive, l'interférométrie reste une technique simple qui permet d'accroître les performances des outils de télédétection sous marine