Van Uffelen Lora J, Worcester Peter F, Dzieciuch Matthew A, Rudnick Daniel L
Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093, USA.
J Acoust Soc Am. 2009 Jun;125(6):3569-88. doi: 10.1121/1.3117430.
Multimegameter-range acoustic data obtained by bottom-mounted receivers show significant acoustic energy penetrating several hundred meters into geometric shadow zones below cusps (caustics) of timefronts computed using climatological databases [B. D. Dushaw et al., IEEE J. Ocean. Eng. 24, 202-214 (1999)]. This penetration is much larger than predicted by diffraction theory. Because these receivers are horizontal arrays, they do not provide information on the vertical structure of the shadow-zone arrivals. Acoustic data from two vertical line array receivers deployed in close proximity in the North Pacific Ocean, together virtually spanning the water column, show the vertical structure of the shadow-zone arrivals for transmissions from broadband 250-Hz sources moored at the sound-channel axis (750 m) and slightly above the surface conjugate depth (3000 m) at ranges of 500 and 1000 km. Comparisons to parabolic equation simulations for sound-speed fields that do not include significant internal-wave variability show that early branches of the measured timefronts consistently penetrate as much as 500-800 m deeper into the water column than predicted. Subsequent parabolic equation simulations incorporating sound-speed fluctuations consistent with the Garrett-Munk internal-wave spectrum at full strength accurately predict the observed energy level to within 3-4-dB rms over the depth range of the shadow-zone arrivals.
由海底接收器获取的多兆米级声学数据显示，显著的声能穿透到了几百米深处，进入到使用气候学数据库计算得到的时前峰（焦散）波峰下方的几何阴影区[B. D. 杜肖等人，《IEEE海洋工程学报》24，202 - 214（1999年）]。这种穿透深度比衍射理论预测的要大得多。由于这些接收器是水平阵列，它们无法提供关于阴影区波至垂直结构的信息。在北太平洋近距离部署的两个垂直线列阵接收器获取的声学数据，实际上覆盖了整个水柱，展示了来自停泊在声道轴（750米）和略高于海面共轭深度（3000米）处的250赫兹宽带声源、距离为500千米和1000千米的传输信号的阴影区波至的垂直结构。与不包含显著内波变化的声速场抛物方程模拟结果相比，实测时前峰的早期分支始终比预测结果多穿透水柱500 - 800米。随后纳入与加勒特 - 蒙克内波谱完全一致的声速波动的抛物方程模拟，在阴影区波至的深度范围内，能将观测到得能量水平准确预测到均方根误差在3 - 4分贝以内。
