Date of Award

Spring 2021

Project Type

Thesis

Program or Major

Ocean Engineering

Degree Name

Master of Science

First Advisor

Anthony Lyons

Second Advisor

Gabriel Venegas

Third Advisor

Jennifer Dijkstra

Abstract

When examining the acoustic response of the seafloor, scattering strength is assumedto be temporally invariant. However, the state of the seafloor in terms of roughness and sediment heterogeneity is not temporally invariant. Changes in both seafloor roughness and sediment heterogeneity are known to correlate with changes in scattering strength. This thesis is a preliminary investigation into the temporal variability of scattering strength. The data for this thesis was collected in three separate experiments at two different sites: 24-30 September, 2020 offshore of New Castle Island; 02-23 October, 2020 offshore of New Castle Island; and 27 October, 2020–12 November, 2020 offshore of Star Island. Analysis of the data from 02-23 October revealed the New Castle Island site to have a range of scattering strengths of at least 5 dB across all frequencies. Lower grazing angles have ranges in excess of 10 dB. The Star Island data from 27 October–12 November and the New Castle Island data from 24–30 September did not show as much variability. The variability for both data sets was frequently within an uncertainty of 1.25 dB. This does not mean there was no variability, as changes in scattering strength of 3-4 dB over time scales of days were observed in both data sets. Causes for the variability in scattering strength and reasons for the differences in variability among the experiments were examined, but definitive conclusions were not reached. The work described by this thesis provides the groundwork for more detailed and extensive experiments that will be performed over the next two years.

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