Sediment Acoustics: Wideband Model, Reflection Loss and Ambient Noise Inversion

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Abstract : Long-term goals are physically sound models of acoustic interaction with the ocean floor including penetration, reflection and scattering in support of MCM and ASW needs. The objectives are: (1) Consolidation of the BIC08 model of sediment acoustics, its verification in a variety of sediment types, parameter reduction and documentation in preparation for transition. (2) A new model of sediment reflection based on a mixture of models suitable for shallow water sonars. (3) Coupling of BIC08 to rough surface scattering models. APPROACH (1) Consolidation of the BIC08 model: This model contains plausible physical processes. It is based on the Biot-Stoll grain contact squirt flow and shear viscous drag (BICSQS) model, which includes squirt flow at the grain-grain contacts [Chotiros, Isakson 2004], combined with improvements in squirt flow modeling, the frame virtual mass extension to account for the random grains rotation [Chotiros, Isakson 2007], and the high-frequency viscous drag correction [Chotiros, Isakson 2008]. The approach is to reconcile common parameters in the different components, and consolidate the input parameters to reduce the parameter count. Further tests are planned to continue to test it against experimental measurements and extend it to a wider variety of ocean sediments, through participation in future shallow-water and sediment acoustics experiments. New experimentation methods are envisioned, including the exploitation of ambient noise for bottom characterization using a compact, partially buried array. (2) A new model of sediment reflection: This is a new approach to modeling ocean sediments that recognizes that the sediment is often patchy. The reflection measurements from the SAX04 experiment [Isakson, Chotiros, Camin, Piper 2010] are an extreme example. This suggests a new approach to modeling bottom reflection as a random process, in which each bottom bounce contains both a deterministic as well as a random component.