Rapid distinction of dumpsite objects using Multiple-Aspect Scattering - Results from scaled tank experiments

Toxic dumpsites on the seafloor are causing increasing environmental concern, but traditional sonar imaging strains to distinguish objects in unconsolidated sediments, in particular in cluttered terrains. Scaled tank experiments were conducted with 4 different cylinders (fluid-filled and solid aluminium, air-filled and solid stainless steel, respectively) and 2 seabed types (silt and gravel), using the facilities at the University of Bath. The setup was a 10:1 scaled version of the EC-SITAR sea trials site in the Stockholm Archipelago (Sweden). The main aim of these experiments was to design efficient surveying strategies, later used at sea. Our studies showed large variations depending on the aspect of these targets and their bistatic imaging configuration. These variations can be directly related to the shapes of the targets (e.g. dimensions, presence of ribs), their content (hollow or solid) and the material of the shells (e.g. stainless steel or aluminium). They are quantified using the combined L norm of the time-domain signals at each aspect. Using appropriate ranges of multistatic configurations and imaging each target at 3 distinct aspects (45° apart), it is possible to successfully distinguish between similar targets with distinct contents and/or material, even in cluttered terrains.