Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA.
J Acoust Soc Am. 2011 Sep;130(3):1173-87. doi: 10.1121/1.3605565.
A study of 400 Hz sound focusing and ducting effects in a packet of curved nonlinear internal waves in shallow water is presented. Sound propagation roughly along the crests of the waves is simulated with a three-dimensional parabolic equation computational code, and the results are compared to measured propagation along fixed 3 and 6 km source/receiver paths. The measurements were made on the shelf of the South China Sea northeast of Tung-Sha Island. Construction of the time-varying three-dimensional sound-speed fields used in the modeling simulations was guided by environmental data collected concurrently with the acoustic data. Computed three-dimensional propagation results compare well with field observations. The simulations allow identification of time-dependent sound forward scattering and ducting processes within the curved internal gravity waves. Strong acoustic intensity enhancement was observed during passage of high-amplitude nonlinear waves over the source/receiver paths, and is replicated in the model. The waves were typical of the region (35 m vertical displacement). Two types of ducting are found in the model, which occur asynchronously. One type is three-dimensional modal trapping in deep ducts within the wave crests (shallow thermocline zones). The second type is surface ducting within the wave troughs (deep thermocline zones).
本文研究了浅水中一包弯曲非线性内波的 400 Hz 聚焦和波导效应。利用三维抛物线方程计算程序对大致沿波峰传播的声音进行了模拟，并将结果与沿固定的 3 公里和 6 公里声源/接收器路径的测量结果进行了比较。测量是在东沙岛东北的南海大陆架上进行的。在建模模拟中，时变三维声速场的构建是由与声数据同时采集的环境数据指导的。计算的三维传播结果与现场观测吻合较好。模拟允许识别弯曲内重力波内的时变声前向散射和波导过程。在源/接收器路径上经过高强度非线性波时，观察到强烈的声强增强，在模型中得到了再现。这些波是该地区的典型波（35 米垂直位移）。在模型中发现了两种类型的波导，它们是异步发生的。一种是在波峰（浅层温跃层区）内的深波导中的三维模态俘获。第二种是在波谷内的表面波导（深层温跃层区）。
