Date of Award

Winter 2008

Project Type

Thesis

Program or Major

Ocean Engineering

Degree Name

Master of Science

First Advisor

Thomas C Weber

Abstract

An acoustic experiment was carried out in October 2007 in Portsmouth Harbor, New Hampshire, to measure the effects of environmental variability on acoustic range measurements over a distance of 948 meters. A fixed source and receiver measured the one-way travel time and signal level fluctuations over four days. Wind, sound speed, tidal data, and current speed predictions were used to assess their effects on the acoustic measurements. The environmental data collected during this experiment showed variability at many scales, both temporally and spatially throughout the harbor. The acoustic data revealed the presence of multipath arrivals, with 2-3 strong arrivals for each transmitted ping. A simple geometric model was used, along with ray-tracing, to describe fluctuations in arrival time and signal level. Acoustic travel times between a fixed source and receiver were converted to range measurements and compared with GPS-derived ranges. This study provides a basis for understanding the capabilities and limitations of acoustic travel time measurements in Portsmouth Harbor, or similar dynamic multipath environments. Results showed an overall spread in range of between five and eight meters over the total range of 948 meters, with greater precision and accuracy possible with additional processing.

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