Twenty-first century outer continental shelf and shelfbreak acoustics research: Methods, tools, and progress

New findings in outer-shelf and shelfbreak acoustics have been enabled by experimental and computational advances over the last 25 years. The details of sound field variability caused by highly dynamic conditions often found in this regime have become measurable through advances in data collection technology. Furthermore, these details can now be computationally modeled more realistically. The coupling of more plentiful data and higher fidelity modeling has uncovered many new behaviors. It has also allowed us to quantify the effects on sound level and phase structure (coherence) of many outer-shelf physical features, as well as the temporal aspects of these variations. Key tools have been vessel dynamic positioning, underwater position finding, small mobile platforms, high-capacity multichannel receive arrays, data-assimilating regional ocean dynamical models, nonlinear wave modeling, and three-dimensional acoustic propagation modeling. Examples from the published work of the authors, and the work of others, of how these advances have fostered new knowledge of specific processes will be presented, as well as present-day challenges inspired by recent findings.