SCALED TANK EXPERIMENTS: SEABED AND TARGET SCATTERING AT HIGH FREQUENCIES

Abstract: Emergent technologies such as Autonomous Underwater Vehicles and bistatic sonars offer immense leverage to the modern applications of underwater acoustics. However, high-frequency scattering processes need to be better understood, especially in complex, multiple-target environments (e.g. dumpsites or highly cluttered seabeds). Sea trials are paramount in providing acoustic measurements to validate scattering models and show the different processes involved, but they are expensive, difficult to conduct, and fraught with difficulties. Laboratory experiments are complementary, because of the fully controlled environment and the repeatability of the measurements. The imaging frequencies (> 10 kHz) to be investigated, and the finite dimensions of the tanks usually employed, mean that these experiments need to be scaled. Our article will first present the differences between sea trials and tank experiments, the various parameters that need to be scaled, and the physical validity of the choices made in each case. We shall then illustrate this by presenting some scaled experiments conducted in our facilities at the University of Bath, in a large water tank containing several sediment trays representative of continental margin seabeds. The first series of scaled experiments correspond to acoustic propagation and penetration in th