Acoustic Measurement of Multisubtidal Internal Modes Generated in Hiroshima Bay, Japan
Acoustic Measurement of Multisubtidal Internal Modes Generated in Hiroshima Bay, Japan
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DOI：
10.1109/joe.2009.2014933
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发表时间：
2009-05
影响因子：
4.1
通讯作者：
H. Nguyen;A. Kaneko;Ju Lin;Keisuke Yamaguchi;N. Gohda;Yoshio Takasugi
中科院分区：
文献类型：
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作者：
H. Nguyen;A. Kaneko;Ju Lin;Keisuke Yamaguchi;N. Gohda;Yoshio Takasugi
在日本广岛湾，尽管由于许多牡蛎养殖筏以及一系列用于种植牡蛎的垂直线串在海湾上广泛分布，导致严重的数据缺口，但通过7个声学站进行的海岸声层析成像（CAT）实验成功地测量了潮汐下的多重内部模态。本文分析了单向和互向传输速率较好的5条传输线的走时数据，重点分析了声速（与温度成正比）的潮下变化。在1.0 ~ 4.0 h的周期范围内观测到显著的多潮下内部模态。为了确定内部模态的源区域，估计其传播速度和方向，对成功传输线沿线距离平均声速的时间序列数据进行了功率谱和交叉谱分析。周期为3.8 ~ 4.2、2.0 ~ 2.3和1.4 ~ 1.5 h的波分别为长内波的第二、第三和第四模态，第一模态属于半日潮。结果表明，内模源区位于层析场东北角的窄通道内，模态从源区向外辐射，满足本研究确定的传播参数（周期、相位速度和传播方向）。也可以通过点温度传感器测量潮下内模的传播参数，将点温度传感器安装在水产养殖筏上，并进行适当的布置。然而，应该注意的是，层析成像技术可以通过沿每条射线路径的空间平均值来确认温度变化。
A coastal acoustic tomography (CAT) experiment with seven acoustic stations was successfully carried out to measure multisubtidal internal modes, generated in Hiroshima Bay, Japan, in spite of severe data gaps due to many oyster aquaculture rafts, accompanied by an array of vertical wire strings for growing oysters and distributed widely over the bay. The travel-time data acquired along five transmission lines with better data acquisition rates in one-way or reciprocal directions are analyzed, focusing on subtidal variations of sound speed (proportional to temperature). Significant multisubtidal internal modes are observed in the period range of 1.0-4.0 h. To specify the source region of internal modes and to estimate their propagation speed and direction, the power-spectral and cross-spectral analyses are applied to the time-series data of range-averaged sound speed along the successful transmission lines. Waves of period ranges 3.8-4.2, 2.0-2.3, and 1.4-1.5 h are identified as the second, third, and fourth modes of long internal waves, respectively, and the first internal mode is attributed to the semidiurnal tide. It is suggested that the source region of internal modes is located in the narrow channel at the northeastern corner of the tomography site and the modes radiate out from the source region, satisfying the propagation parameters (period, phase speed, and propagation direction) determined by this study. The propagation parameters of the subtidal internal modes can also be measured by point temperature sensors, attached to aquaculture rafts with an appropriate arrangement. However, it should be noted that the tomographic technique can confirm temperature variations through a spatial average along each ray path.