Seabed characterization using ambient noise and compact arrays on an autonomous underwater vehicle

Abstract

Estimating the seabed geoacoustic properties at various fidelity levels has been a research topic for several decades. The majority of the applied seabed characterization techniques often require significant involvement of surface vessels, complex experimental setup and human interaction. Technical advances in underwater autonomy and the development of energy efficient electronics provide new opportunities to optimize underwater environmental surveys in particular of the seabed. In 2012, the CMRE conducted the GLASS'12 experiment in the Mediterranean Sea with the objective to investigate the feasibility of utilizing a hybrid autonomous underwater vehicle equipped with a compact nose array for long-duration seabed characterization over large areas. The vehicle has the capability of operating in traditional propulsion and glider mode, and the nose-mounted array consists of a 5-element vertical and 4-element tetrahedral array. The sound sources used as information carrier were ambient noise, e.g. sea surface generated noise and loud distant sources of opportunity. The experimental setup together with the newly developed autonomous equipment will be presented and examples of inferred reflection loss and sub-bottom profiling from the ambient noise are compared to ground truth measurements.

Recursive Bayesian synthetic aperture geoacoustic inversion in the presence of motion dynamics

“…4 and 37) [see Eqs. (18) and (19)- (22)]. A way of generating these metrics is Monte Carlo integration and importance sampling.…”

“…Using Eqs. 21, (22), (27), and (28), Fig. 5 shows both one-dimensional (1-D) (along the diagonal) and two-dimensional (2-D) (off-diagonal) marginal PPDs.…”

“…20 AUV-based inversions recently have been gaining research interest due to their operational attractiveness. [21][22][23][24] The theory of waveguide Doppler and modal propagation is reviewed briefly in Sec. II, followed by the formulation of the inversion problem.…”