Three-dimensional numerical simulation of sound waves propagating near the west coast of Brittany

Abstract

Numerical results of sound wave propagation in a realistic three-dimensional (3-D) oceanic environment are reported. The region of interest is the west coast of Brittany, near the harbor of Brest, France. The numerical simulations were performed running a fully 3-D parabolic equation based code considering omnidirectional point sources emitting at low frequencies (e.g. 50—100 Hz) and located in the water column near the entrance of the strait linking the roadstead of Brest to the Atlantic Ocean (also known as 'Goulet de Brest'). Numerical simulations clearly show that, depending on position of the acoustic sources, sound waves can be strongly affected by out-of-plane propagation effects resulting from complicated multiple reflections off the sloping bottom and channeling effects due to the three-dimensionally varying bathymetry in this particular region, and hence can predict interesting modal arrivals at specific receivers (with typical source-receiver distances of 30 km), not predicted by two-dimensional models. Note that the 3-D effects predicted here for a realistic marine environment are very similar to the ones described in detail for (now classical) benchmark problems (e.g. 3-D wedge and 3-D canyon test cases), though the environmental parameters are different. Several source depths and positions are investigated.