Impact on acoustic propagation by internal waves and tides in the region of shelf and slope.

Abstract

Internal waves (IWS) and tidal activities were investigated in the South China Sea (SCS) and the northeastern seas of Taiwan. These oceanic processes cause large fluctuations and impact on underwater acoustic propagation. These effects include two-dimensional (2-D) and three-dimensional (3-D) effects. The 2-D and 3-D effects are related to the angle between the directions of sound propagation and IW front. When the IW front are from 20 to 90 deg with respect to the acoustic propagation direction, acoustic mode coupling is the dominant factor which could be sufficiently predicted by the N×2D simulations. Acoustic energy is exchanged between modes and is re-distributed among the water columns. However, when the angles between the wave front and the acoustic wave propagation are 0–20 deg, the horizontal refraction effect dominates over mode coupling and the fully 3-D calculation is needed. The acoustic energy would be refracted, as a consequence, resulting in energy focusing and defocusing. These effects are clearly seen by the series of data collected in the SCS and the region of Northern East of Taiwan. Computer modeling results are used to manifest experiment data results in this research. [This work is supported by National Science Council of Taiwan.]