Underwater environment restitution through sonar images and swath bathymetry rendering
Résumé
Accurately 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.