Design of the acoustic tomography system for velocity measurement with an application to the coastal sea.

Abstract

An acoustic tomography system has been designed with an aim to long-term velocitymeasurement in coastal oceans. In this system, Travel times of sound waves propagatingreciprocally between two acoustic stations are measured accurately by using I kHz pulsesignals from GPS (global positioning system). The S/N ratio of signals received is remarkablyincreased by use of the M sequence (maximum period sequence) and arrayed hydrophones.Beamforming also makes it possible to determine the incident angle of signalsreaching the arrayed hydrophones. This system was successfully applied to a 10-km scalevelocity measurement in the Seto Inland Sea, Japan. Path-averaged velocities estimatedfrom the reciprocal transmission data were in satisfactory agreement with the result of the ADCP (acoustic Doppler current profiler) measurement which had been carried out at thesame site for cross comparison. This study provides us a promising step to the full-scalecoastal tomography experiment, performed by a number of acoustic stations which surroundthe coastal regions such as bays and straits.