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Presenter: Li Zhou
Supervisor: Dr. Adam Zielinski

Date: Fri, August 20, 2010
Time: 09:00:00 - 10:00:00
Place: EOW 430

ABSTRACT

ABSTRACT:

Positioning an underwater object with respect to a reference point is required in diverse areas in ocean scientific and engineering undertakings. Underwater acoustic positioning systems are designed to operate from a reference point and employ external transducers or transducer arrays as aids for positioning. Traditional positioning methods rely on measuring of time-of-flight of an acoustic signal travelling from the target to the reference platform, by means of the cross-correlation method. The positioning accuracy of conventional underwater positioning systems varies from a few centimetres to meters, depending on the operating range, operating depth, and working frequency. A novel positioning method was proposed which takes advantages of a tether cable between the reference platform and the target. This method conducts positioning via continuous phase measurement between a reference signal and the acoustic signal transmitted by the target. We name it as the Positioning-based-on-Phase-Measurement (PPM) method. Under ideal conditions, the positioning error of the PPM method is proportional to the phase measurement error, with a fraction of the transmitted signal's wavelength.The PPM method can be used to position an underwater moving object such as a remotely operated vehicle (ROV) or a bottom crawler. It can also be used to measure the ocean currents speed over a path, or to monitor the movements of tectonic plates. We will investigate the environmental fluctuations in practical underwater medium and their effects on the positioning accuracy. Scale-down experiments in air using ultrasonic transmission were conducted and verified the effectiveness of the proposed positioning method.