Beamforming through an anisotropic, time-varying internal wave field

Abstract

Shallow-water environments commonly exhibit complex spatial and temporal variations in temperature and salinity caused by internal wave activity. These quantities map into a sound-speed distribution that can significantly distort both the amplitude and phase of an acoustic field propagating through the environment. This presentation describes computer simulation results on the effect of an anisotropic, time-varying internal wave field on plane wave beamforming of a point source within a shallow-water waveguide. The (azimuthal) anisotropy is described by a solitary wave packet propagating through the region. A 3D parabolic equation code was used to propagate a 400-Hz signal through this space and time-evolving environment. Beamformed power, parametrized by receiver depth and an azimuthal angle, is illustrated for horizontal arrays and presented in terms of beam space, time, and range from the source. When the packet enters the region between source and receiving array, significant periodic beam wander and beam splitting are seen; such effects are shown to be related to horizontal refraction of energy from individual internal wave depressions forming the solitary wave packet. [Work supported by the Office of Naval Research.]