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

Abstract

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 four different cylinders (fluid-filled and solid aluminium, air-filled and solid stainless steel, respectively) and two 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 L4 norm of the time-domain signals at each aspect. Using appropriate ranges of multistatic configurations and imaging each target at three distinct aspects (45° apart), it is possible to successfully distinguish between similar targets with distinct contents and/or material, even in cluttered terrains.

Multistatic acoustic characterization of seabed targets

“…This aligns with Blondel's multistatic classification results, 13 which showed that different bistatic angles provided different information on target characteristics over the three aspect angles he examined.…”

“…Simulation studies have been conducted in the multistatic space for spherical and cylindrical targets by Schmidt, Zampolli, and others to explore the implications of multiple mobile sources and receivers in a sonar network. [9][10][11] Tank and pond experiments by Dobbins, Blondel, Waters, and others [12][13][14][15][16] looked at different aspect angles on targets in a partial investigation of the multistatic scattering space. Ji et al describe simulation and tank experiments that include data collection on cylinders to examine impact of aspect and bistatic angle on scattering over a limited range of bistatic angles.…”

“…25 In the most relevant prior work, classification of target in the multistatic space using the L4 norm versus scattering angle was investigated by Blondel in tank experiments. 13 Blondel looked at scattering for three target aspect angles and multiple corresponding bistatic angles for targets with different composition, and found differences between the targets when multiple bistatic angles were observed. He also observed that the bistatic angle impacted the strength of the classification.…”