Page 36 - Fall2019

Computational Acoustics in Oceanography
There are many motivations for modeling underwater noise. All human uses of active underwater sound (using gener- ated sound signals) are subject to the signal-to-noise ratio at the receivers. If fully masked by noise, the sound is not usable. Additionally, marine mammals and other creatures are affected by underwater sound, both natural and anthro- pogenic. The levels of anthropogenic sound reaching marine mammals in their natural habitats can be estimated using verified noise models. One can easily imagine sound from multiple sources of known location, such as ships and break- ing ocean waves from gales, each being modeled as outgoing in three dimensions, with the power from each summed everywhere to produce 3-D maps of noise. At the present time, noise models use ocean propagation conditions taken from ocean models (Figure 5), which, of course, do not fully match reality. This means that modeled noise fields will have uncertainty, to be evaluated most reliably with experiments.
Summary
We hope to have provided insight into the reasons why computed acoustic fields are so commonly incorporated into many types of oceanographic research. Both naturally occurring and man-made sounds can be used to learn about processes in the sea. Detailed knowledge of how the sound moves through the ocean, obtainable in many situations with computational methods, allows more of the information in the sound signals to be tapped for research purposes.
Acknowledgments
We thank the US Office of Naval Research for support. Timothy F. Duda acknowledges additional support from the Walter A. and Hope Noyes Smith Chair for Excellence in Oceanography award at WHOI (2019).
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