Sonar images and swath bathymetry simulations for environment restitution through acoustical ray tracing techniques
Résumé
Due to operational constraints for underwater data acquisition, simulating realistic sonar images and swath bathymetry profiles is crucial for tuning detection and classification algorithms according to sensors settings and sea-bottom nature and relief. Therefore, we developped such a simulator relying on acoustical ray tracing techniques tailored for considering specific underwater propagation properties. It aims at rendering data similar to what real sensors provide in a natural context. In the proposed approach, the virtual environment gathers fractal simulated or real elevation map for sea-ground truth, sets of natural or manufactured bottom-laying items and sea-bed textures resulting from adequate spatial layouts of ground resolution cells. Moreover, taking into account carrier trajectory and attitude along time warrants multi-sensor realistic outputs. Thus, sonar images generation involves specular and diffused backscattering components, multi-path sound propagation, adaptative ray oversampling to modelize acoustic lobe configuration. Concerning swath bathymetry charts, response of scattering cells allows to estimate elevation profiles through differential phase returns simulation. Indeed, a geometrical computation provides an ideal differential phase on which are applied various noise laws corresponding to behaviours learned from real data. A parallel conception and implementation of the algorithms give delightful results for training sonar images processings (fuzzy segmentation, detection, classification, symbolic registration, ...). Given the simulator flexibility, a promizing 3D sea-bottom and objects reconstruction method takes benefit of information issued from multiple points of view.