Performance optimised reverberation modelling for real-time synthesis of sidescan sonar imagery

In this thesis a novel performance optimised approach to sidescan sonar simulation is described. Seminal approaches to sonar simulation reported in the literature are seen to produce visually realistic results that are verified using statistical and spectral methods. The problem is that the computational implementations of the underlying acoustic models are numerically intensive to an extent that prohibits real-time implementation. It is shown in this thesis that for sonar imaging simulations, the principal performance-limiting factor is the method of processing applied to the highly intricate and excessively detailed polygonal mesh required to accurately model seafloor reverberation. By current techniques, discovery of ensonifed facets at each ping requires direct interrogation of each facet constructing the seafloor mesh to determine its contribution to the backscattered imagery. The inherent computational bottleneck significantly arrests the runtime performance delivered by the simulation. From a literature review it emerged that the performance-related challenges to be overcome in sonar simulation have direct parallels with those encountered in the field of 3D graphics rendering when processing object models for interactive visualisation. Several schemes presented in the computer graphics literature to address this issue are identified in this thesis as suitable candidates to accelerate sonar simulation. A novel sidescan sonar simulator is then implemented by incorporating a mesh abstraction pipeline within the simulation process to dynamically adapt the local seafloor geometry according to its spatial proximity to the roving sonar fanbeam footprint. In the resulting transitional multi-resolution mesh, the ensonifed swathe is described at its full original resolution and geometry, while non-ensonifed regions are described by orders of magnitude fewer geometric primitives. The new approach to sonar simulation is experimentally tested and the results show it to offer a performance acceleration translating to an orders of magnitude improvement in simulation response times. Most important, it is also shown that the increased simulation throughput effectively translates current sonar simulation technology from offline to online application while affecting no degradation to the integrity of simulator-generated imagery