Deep Water Acoustics
Technical Report,01 Jan 2013,31 Mar 2016
University of Washington - Applied Physics Laboratory Seattle United States
Pagination or Media Count:
A mechanism is presented by which the observed acoustic intensity is made to vary due to changes in the acoustic path that are caused by internal-tide vertical fluid displacements. The position in range and depth of large-scale caustic structure is determined by the background sound-speed profile. Internal tides cause a deformation of the background profile, which changes the positions of the caustic structuresintroducing slow intensity changes at a fixed position in depth and range. Parabolic equation and Hamiltonian ray-tracing calculations indicate that internal tides could cause enhanced variability in the intensity in the form of slow changes. Furthermore, the calculations demonstrate how large-scale perturbations to the index of refraction can result in intensity fluctuations--contrary to conclusions of previous theoretical work.