The mode view of long-range propagation through oceanic internal waves

Abstract

For long-range acoustic propagation in the ocean, calculation of internal wave effects by ray tracing is far from accurate. Full wave methods must be used. An unperturbed normal mode simulation has been developed for this case. Simulations have been carried out with a single-mode starting field, with a sound speed profile measured in the 2010 Philippine Sea experiment, and internal waves consistent with measurements at the same region and same time. Modes were chosen that turn around half way between the sound axis and the surface. The frequency is 100 Hz, appropriate for long-range propagation experiments. Ensemble averaged mode intensities are consistent with transport theory results, but the individual mode intensities as a function of range are very inconsistent with a random walk ("diffusion") in mode number space.