IMIS

The experiment involved reciprocal transmissions at 30 s intervals for 4 days with two 7 kHz broadband transceivers. To determine the origin and potential interpretive value of the frequent multiple arrivals in the unstratified, highly-turbulent flow conditions, we performed a series of simulations with the Bellhop3D model. We demonstrate that the multiple arrivals mainly arise from out-of-plane sound propagation p aths resulting from the effects of the local bathymetry. The maximum mean difference between FAT-estimated currents and the coincident moving-vessel ADCP transects is found to be less than 10%. Comparisons are also made between velocity spectra during the full flood and ebb determined using the FAT velocities and the vertically-averaged velocities from a bottom-mounted ADCP deployed in a later experiment. The spectra exhibit similar shapes in the frequency and wavenumber overlap regions, indicating that FAT is able to detect macro-turbulence. Good agreement is also obtained between the sound-speed estimates based on travel time and those from in-situ temperature and salinity data.