Title

The influence of oceanic internal waves on the phase stability of broadband acoustic transmission at long range

Date of Award

1999

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Michael G. Brown, Committee Chair

Abstract

Instantaneous phase stability in acoustic wavefields measured during the 1994 Acoustic Engineering Test (AET) is examined. AET is one of several preliminary Acoustic Thermometry of Ocean Climate (ATOC) experiments conducted in the past several years. Internal waves are assumed to be the mechanism responsible for phase decorrelation over time scales of ten to thirty minutes. The AET experiment had a center frequency of 75 Hz and a 3 megameter path length. Comparison of numerical simulations to experimental results provide insight into how internal waves scatter sound and can be used to constrain statistical descriptors of realistic deep ocean internal wave fields. Ray-based wavefield simulations are performed using both Deterministic Ray Theory (DRT) and Stochastic Ray Theory (SRT), while full wave simulations are performed using the co insensitive parabolic equation model. This work complements recent similar inference studies of Colosi et al. (1994) and Heaney (1997) on other preliminary ATOC experiments. Working within the framework of the Garrett-Munk internal wave spectrum, phase coherence time, which was observed to be roughly ten to fifteen minutes in the AET experiment, is found to be dependent on the vertically integrated potential energy density, &egr;, and the bounds on the horizontal wavenumber spectrum, k min and kmax. Results suggest that phase coherence is insensitive to mode number cutoff, jmax . Two manifestations of the phase decorrelation observed in simulations are studied. Temporal wavefront wander as defined by Flatte et al. (1979) is examined over the decorrelation period as a function of the horizontal wavenumber spectrum. Intermittent structure that appears and disappears throughout the wavefront on time scales of ten to thirty minutes is examined. This intermittent structure is observed in both full wave modeling and DRT but not SRT.

Keywords

Engineering, Marine and Ocean; Physics, Acoustics

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9934281