Real-Time Offshore Coastal Acoustic Tomography Enabled With Mirror-Transpond Functionality

Abstract

Real-time offshore coastal acoustic tomography (CAT) with mirror-transpond functionality is the most recent feature added to CAT to transfer travel-time data obtained in an offshore subsurface station to a shore station in real time, forming a round-trip travel time by original transmission and subsequent mirror transmission. The minimum unit, composed of one land and one offshore system, was operated to validate the performance of CAT with mirror-transpond functionality (MCAT) in the feasibility experiment, which was carried out in April 2017 in the Nekoseto Strait of the Seto Inland Sea, Japan. The root-mean-square error (RMSE) of the hourly mean range-average currents calculated from the original-original and original-mirror reciprocal travel-time pairs was 0.05 ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , significantly smaller than the variation range of the semidiurnal tidal current (0.2-0.3 ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) dominant at the experimental site. The RMSE for the residual current was also significantly smaller than its variation range. This study suggests the feasibility of using a compact MCAT array composed of one land and three offshore stations.