Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2011
Description:
This thesis describes the physics of fully three-dimensional low frequency acoustic interaction
with internal waves, bottom sediment waves and surface swell waves that are
often observed in shallow waters and on continental slopes. A simple idealized model
of the ocean waveguide is used to analytically study the properties of acoustic normal
modes and their perturbations due to waves of each type. The combined approach
of a semi-quantitative study based on the geometrical acoustics approximation and
on fully three-dimensional coupled mode numerical modeling is used to examine the
azimuthal dependence of sound wave horizontal reflection from, transmission through
and ducting between straight parallel waves of each type. The impact of the natural
crossings of nonlinear internal waves on horizontally ducted sound energy is studied
theoretically and modeled numerically using a three-dimensional parabolic equation
acoustic propagation code. A realistic sea surface elevation is synthesized from the directional
spectrum of long swells and used for three-dimensional numerical modeling
of acoustic propagation. As a result, considerable normal mode amplitude scintillations
were observed and shown to be strongly dependent on horizontal azimuth, range
and mode number. Full field numerical modeling of low frequency sound propagation
through large sand waves located on a sloped bottom was performed using the
high resolution bathymetry of the mouth of San Francisco Bay. Very strong acoustic
ducting is shown to steer acoustic energy beams along the sand wave’s curved crests.
Description:
Office of Naval Research for the financial
support of this work.
Keywords:
Acoustic models
;
Internal waves
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
