Multipath tracking and acoustical oceanography measurements in a stratified coastal tidal channel
Barton, Alan Dodd
MetadataShow full item record
A high-frequency (67 kHz) acoustical scintillation experiment was carrier out in the northern entrance to Hood Canal, Puget Sound, WA. This experiment made use of a 4-transmitter and 4-receiver array contigured in a T-shape. The two-dimensional feature of this array was designed to measure both along-channel small-scall properties as a result of advection and vertical properties as a result of acoustic regraction from temperature/salinity stratification. With long path lengths and stratified conditions, acoustic propagation resulted in multipath arrivals which were separable for most of the measurement period. A maximum likelihood estimation algorithm is developed that tracks both the direct path signal at approximately 25-30 m depth and the upward refracted signal into the near surface and calculates amplitude, phase, and travel time for each. The acoustical signals are then inverted to estimate alon channel flow properties, turbulent effective refractive index levels, and changes in stratification. Along-channel flows exceed 60 cm s -1 on strong ebb and the acoustic measurements agree with a tidal model of the currents. Both scalar and vector contributions to the turbulence are analyzed, and show that scalar variability dominates the scattering. The vertical acoustic arrival angle to first order appears to be a sensitive indicator of stratification changes. Finally, analysis of a near surface path shows that surface waves are the dominant contributor to the acoustic amplitude and phase fluctuations and horizontal coherence measurements remain high during a time of weak winds.