Design and testing of an acoustic ultra-short baseline navigation system

by Brian Hearne Tracey Submitted to the Department of Ocean Engineering on 30 July 1992 in partial fulfillment of the requirements for the Degree of Master of Science in Ocean Engineering An ultra-short baseline acoustic navigation system has been developed which is capable of determining bearing to a sound source with an error of less than 1° in typical operational conditions. The system has a demonstrated ability to operate in an environment in which multipath interference is significant. A DSP microprocessor is used to process signals received by two hydrophones from a 26 kHz toneburst sound source. This processing power is used to implement features not commonly available with commercial systems. The system has the capability to make an on-line measurement of the signal-tonoise ratio, which can be used to estimate the confidence which should be placed in the data. Estimates of phase difference and signal power are generated many times within each received pulse, so the effects of multi path interference throughout the pulse can be observed. Results of tests at several ranges are presented, and compared to performance models developed in the thesis. System performance is quantified, and an effort is made to understand the effects of multipath arrivals. Technical Supervisor: James G. Bellingham Title: Research Engineer, MIT Sea Grant Underwater Vehicles Lab Thesis Supervisor: Henrik Schmidt Title: Professor of Ocean Engineering