Acoustic travel time perturbations due to an internal tide and internal wave field in the Barents Sea.

158 Pages·1993·5.3 MB·en_US

by  Ray, Douglas Scott.

vULfcYKNOXLIBRAR.
NAVAL POSTGRADUATE SCHOOI
.^NfEREY CA 93943-5101

Acoustic Travel Time Perturbations due to an Internal
Tide and Internal Wave Field in the Barents Sea
by
Douglas Scott Ray
B.S. Mechanical Engineering
United States Naval Academy (1980)
Submitted in partial fulfillment of the requirements for the degree of
OCEAN ENGINEER
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
and
WOODS HOLE OCEANOGRAPHIC INSTITUTION
August 1993
©
Douglas Scott Ray, MCMXCIII. All rights reserved.
The author hereby grants to MIT, WHOI and the U.S. Government permission to
reproduce and to distribute copies of this thesis document in whole or in part.

DUDLEY KNOX LIBRARY
NAVAL POSTGRADUATE SCHOOI
MONTEREY CA 93943-5101
Acoustic Travel Time Perturbations due to an Internal
Tide and Internal Wave Field in the Barents Sea
by
Douglas Scott Ray
Submitted to the Department of Ocean Engineering, Massachussetts Institute of
Technology,
and the Joint Program in Oceanography and Oceanographic Engineering,
Massachussetts Institute of Technology/Woods Hole Oceanographic Institution
on August 6, 1993, in partial fulfillment of the
requirements for the degree of
OCEAN ENGINEER
Abstract
Travel time perturbations of adiabatic normal modes due to an internal tide and
internal mode field in the Barents Sea are examined. A formalism for the travel time
perturbation due to a change in sound speed is presented. Internal tide and internal
wave amplitude spectra are calculated from Brancker temperature loggers which were
deployed on moorings in the Barents Sea during the August 1992 Barents Sea Polar
Front Experiment. In particular, the first three internal wave mode amplitudes are
estimated from the four Brancker temperature loggers on the southwest mooring of
the array. Modal perturbations in acoustic pulse travel time and the travel time
covariance are calculated and compared for consistency to a simple ray model. These
perturbations are small for the modal arrivals that the vertical acoustic array which
was deployed is expected to resolve. The third internal wave mode has the largest
impact on the acoustic arrivals, per unit amplitude, but the first internal wave mode
dominates the scattering due to having a much larger amplitude overall.
Thesis Supervisor: Dr. James F. Lynch
Title: Associate Scientist
Woods Hole Oceanographic Institution