Grigorieva Natalie S, Fridman Gregory M, Mercer James A, Andrew Rex K, Wolfson Michael A, Howe Bruce M, Colosi John A
St Petersburg State Marine Technical University, St Petersburg, Russia.
J Acoust Soc Am. 2009 Apr;125(4):1919-29. doi: 10.1121/1.3082112.
Propagation of energy along the sound channel axis cannot be formally described in terms of geometrical acoustics due to repeated cusped caustics along the axis. In neighborhoods of these cusped caustics, a very complicated interference pattern is observed. Neighborhoods of interference grow with range and overlap at long ranges. This results in the formation of a complex interference wave--the axial wave--that propagates along the sound channel axis like a wave belonging to a crescendo of near-axial arrivals. The principal properties of this wave are calculated for the actual space-time configuration realized during a 2004 long-range propagation experiment conducted in the North Pacific. The experiment used M-sequences at 68.2 and 75 Hz, transmitter depths from 350 to 800 m, and ranges from 50 to 3200 km. Calculations show that the axial wave would be detectable for an optimal geometry-both transmitter and receiver at the sound channel axis--for a "smooth" range-dependent sound speed field. The addition of sound speed perturbations--induced here by simulated internal waves--randomizes the acoustic field to the extent that the axial wave becomes undetectable. These results should be typical for mid-latitude oceans with similar curvatures about the sound speed minimum.
由于沿声道轴存在重复的尖点焦散，能量沿声道轴的传播无法用几何声学进行形式化描述。在这些尖点焦散的邻域内，会观察到非常复杂的干涉图样。干涉邻域随距离增长，并在远距离处重叠。这导致形成一个复杂的干涉波——轴向波，它沿声道轴传播，就像属于近轴向到达的渐强波一样。针对2004年在北太平洋进行的一次远程传播实验中实现的实际时空配置，计算了该波的主要特性。该实验使用了68.2赫兹和75赫兹的M序列，发射器深度为350至800米，距离为50至3200千米。计算表明，对于“平滑”的距离依赖声速场，在最佳几何配置（发射器和接收器都位于声道轴）下，轴向波是可检测的。添加由模拟内波引起的声速扰动会使声场随机化，以至于轴向波变得不可检测。对于声速最小值处具有相似曲率的中纬度海洋，这些结果应该是典型的。
