Application of acoustic tomography in shallow waters

This paper briefly introduces a state-of-the-art timeof- travel sensor that enables application of acoustic tomography for measuring range-averaged current velocity in extremely shallow waters. The system is called Fluvial Acoustic Tomography and has been developed in Hiroshima University. The paper presents two experiments, the first of which aims at evaluating FAT accuracy in measuring mean flow direction and velocity in an estuarine environment characterized by strong stratification. Second study investigates the applicability of FAT for long-term continuous monitoring of tidal currents in a narrow strait, where is a potential site for installation of a small tidal turbine. During each experiment a set of reference data was collected using a moving-boat ADCP. The results obtained in the first campaign indicate remarkable consistency between FAT and ADCP. It was found that the relative error in the mean flow directions reported by FAT and ADCP did not exceed 10%. The results obtained in the second experiment indicate the agreement between tomographically derived velocities with ADCP in coastal areas. The results also signify the importance of angularity error involved in recovering flow velocity when FAT with only one raypath is used.