Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2000
Description:
A channel characterization experiment for the underwater acoustic communication channel was
carried out at Scripps Pier in May 1999. The experiment investigated acoustic transmission in
very shallow water and breaking waves. In analyzing the data, several questions arose.
The majority of the acoustic channel probe data was corrupted by crosstalk in the receiver array
cable. This thesis investigates methods to correct for the effects of the crosstalk, to attempt to
recover the channel probe data. In selected regions, the crosstalk could be removed quite effectively
using a linear least-squares method to estimate the crosstalk coefficients. The bulk of the data
could not be corrected, however, primarily due to crosstalk from a receiver channel which was not
recorded, and hence could not be well estimated.
A second question addressed by this thesis is concerned with acoustic propagation in shallow water
under bubble clouds. The breaking waves injected air deep into the water column. The resulting
bubble clouds heavily attenuated acoustic signals, effectively causing total dropouts of the acoustic communication channel. Due to buoyancy, the bubbles gradually rise, and the communication
channel clears. The channel clearing was significantly slower than predicted by geometric ray
acoustic propagation models, however. Proposed explanations included secondary, unobserved,
breaking events causing additional bubble injection; delayed rising of bubbles due to turbulent
currents; or failure of the geometric ray model due to suppression by bubble clouds of acoustic
signals which are not along the geometric ray paths. This thesis investigated the final hypothesis,
modeling the acoustic propagation in Scripps Pier environment, using the full wave equation modeling package OASES. It was determined that the attenuation of the propagating acoustic signal
is not accurately predicted by the bubble-induced attenuation along the geometric ray path.
Description:
For financial support, thanks to the National Science Foundation for funding me on a Graduate
Research Fellowship, and thanks to the WHOI Education Office for supplementing that fellowship.
Keywords:
Underwater acoustics
;
Acoustic surface waves
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
Permalink
