Date of Award

Fall 2018

Project Type

Thesis

Program or Major

Ocean Engineering

Degree Name

Master of Science

First Advisor

John E Hughes Clarke

Second Advisor

Andrew Armstrong

Third Advisor

Giuseppe Masetti

Abstract

Internal waves are a common phenomenon associated with stratification developed in shallow tidal seas during summer time. From a hydrographic point of view, they result in very rapid undulations in the main velocline which, if not accounted for, will result in significant refraction errors in multibeam echo sounder data. Mechanical sound speed profiling, both static and mobile, cannot sample this structure adequately (Hughes Clarke, 2017). Thus, an alternate means of detecting and accounting for that variability is needed.

Within the oceanographic community, it has long been recognized that a distinct acoustic volume scattering layer is often associated within or close to major oceanographic boundaries. This has been noted to reflect a combination of temperature/salinity microstructure and zooplankton around the pycnocline depth. Several weeks of multibeam survey on the Irish continental shelf were undertaken during which multispectral acoustic scattering data from a Simrad EK60 scientific echo sounder were acquired together with profiles from a Moving Vessel Profiler.

This thesis proposes and implements a method to determine the evolving sound speed structure by processing the images derived from the EK60 echo sounder. This is done by extracting the scattering layer depth and finding the correlations with the velocline found in each of the discrete MVP profiles. Thus, a continuously evolving estimate of the local sound speed structure is derived. From this, by calculating the associated depth bias in the seafloor modeling caused by the difference in sound speed structure between the last actual profile and the estimate at each ping, a visual indication of the need for a new in situ measurement is made. In this manner, the sound speed structure may be monitored to adjust the spatial and temporal resolutions of the profile casts more efficiently.

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