Performance of a Horizontally Scanning Doppler Sonar Near Shore

In August 1990, tests were performed to investigate the usefulness of a horizontally scanning Doppler acoustic technique in shallow water. Comparisons of radial velocity estimates from a vertical fan beam versus a horizontally aimed pencil beam indicate no degradation attributable to multiple reflections from the surface and bottom. Further tests, in which ping-to-ping phase-coherent means are examined, indicate negligible stationary backscatter from the bottom. Tests in which the acoustic beams were directed shoreward indicate that an extremely dense bubble cloud formed by plunging breakers produces an impenetrable “wall” at the breakpoint, at acoustic frequencies near 195 kHz. Useful velocity estimates (one component) are obtainable everywhere seaward of the breakpoint of the incoming surf. The spatially extensive velocity estimates offered by this technique provide enormous potential for the study of horizontal currents and wave-current interactions in shallow water. ____________________________