Short-Range Acoustic Propagation Variability on a Shelf Area with Strong Nonlinear Internal Waves

During April 2007 a six-day long experiment was conducted to measure internal waves and their acoustic effects at a continental shelf site in the Northern South China Sea. The site is slightly west of the edge of the shelf. At the shelf edge, large internal waves originating in the Luzon Strait area enter shallow water from deep water, undergoing rapid dissipation and wave shape evolution. A moored acoustic source transmitted 400-Hz pulses 3.0 and 6.0 km to two moored vertical line arrays, with geometry such that the propagation path was roughly parallel to the crests of the strongest passing internal waves, so that strong horizontal refraction effects are expected. Internal-wave characteristics and effects of the internal waves on the sound propagation, both observed and modeled, are shown here.