Using broadband acoustic signals and modal behavior to assess scales of ocean variability in shallow water waveguides

The sound speed fields of the continental shelf water column are anisotropic and have “fronts” related to propagating internal wave packets. The angle between a broadband acoustic signal’s source–receiver propagation track and the propagating “fronts” affects its modal composition. If the temporal variability of the modal behavior of the acoustic signals are monitored in time and space, one might identify the fluid process that causes the changes to the sound speed field. In this paper, we first present a heuristic view of how the modal properties of broadband signals can be affected by the sound speed field variability caused by propagating internal wave packets. We then present three days of acoustic field data acquired on vertical and horizontal arrays placed in ~100 m of water about 20 km from the location of acoustic signal sources. Temporal changes in the received acoustic signal's modal composition will be compared to numerical simulations. The changes in modal composition will be correlated to internal wave induced variability in the horizontal refraction of the signals.