Quantitative high-resolution acoustic imaging of the seafloor

Quantifying the properties of the seafloor interface and near surface (a few tens of meters) is of considerable interest to science as well as industry. Scales of interest range from the order of tens of kilometers (survey size) down to less than a centimeter. These scales can be probed using an AUV equipped with a broadband source and a short streamer. The data are processed for energy (rather than peak) reflection coefficients and scattering cross-section versus bi-static angle. In order to tackle spatial scales ranging over 8 orders of magnitude of, it is useful to divide the parameter space into deterministic and stochastic parameters. The energy reflection coefficients contain information on deterministic properties including sound speed, density and attenuation vs depth in the upper tens of meters of sediment. Vertical resolution is a function of depth, but typically of order 0.1 m near surface. The statistical properties of the smaller scales, i.e., seafloor roughness and/or volume heterogeneities are obtained from the bi-static scattering data. Physics-based models are used to relate the sediment micro-structure (the Buckingham model) and sediment fluctuations (the Von Karman spectrum) to the acoustic observables. Quantitative parameter and inter-parameter uncertainties are obtained from Bayesian methods for both deterministic and stochastic parameters.