Numerical Acoustical Monitoring of the Second Mode Internal Solitary Wave near Dongsha Atoll

本文旨在探討以干涉模型頻移方式察測東沙島礁近域孤立內波第二重力模態的可能性。研究係以數值模式針對東沙島礁的南中國海北側的大陸架棚淺水海域，並以此海域之現場實測孤立內波資料進行分析。為了計算三維環境中的聲場係以垂直模態與水平射逼近方式來達成。定置的傳音途徑係轉向垂直於內波偏愛的傳動方向，海床上置放一聲源與數個聲音接受器。聲音接受器被分別置放於水平折射顯著及無相關性的不同範圍。數值模式分析結果顯示當第二孤立內波模態跨越傳音途徑時，一些聲波波導出現聚焦現象，一些則在水平面出現反聚焦現象。研究結果顯示，只要在水平折射效應微弱時，孤立內波的第二模態參數才能從聲波接受訊號波譜的頻移分析中被成功地重新建構。

關鍵字

孤立內波；第二重力模態；頻移；東沙島礁

並列摘要

The possibility of monitoring second gravity mode internal solitons near the Dongsha Atoll by using interference pattern frequency shifts is discussed. The investigation is carried out for the shelf of the nothern South China Sea near the Dongsha Atoll by means of numerical modeling. We use the data of the in-situ internal solitons measurements in this area. The ”vertical modes and horizontal rays” approach is implemented to calculate the low frequency sound fields in the 3D environment. Stationary acoustic path is oriented at the right angle to the preferred internal wave propagation direction. A sound source and receivers are deployed at the sea bottom. Sound receivers are located at the different ranges where horizontal refraction is pronounced, and where it is insignificant. Numerical experiments demonstrate that some of acoustic waveguide modes are focused, and others are defocused in the horizontal plane when the second mode soliton propagates across the acoustic path. It is shown that the second mode internal solitary wave parameters can be successfully reconstructed from the frequency shifts in the spectrum of received signals only if horizontal refraction effects are weak.

並列關鍵字

internal soliton ； second gravitional mode ； frequency shift ； Dongsha Atoll

國際替代計量

Numerical Acoustical Monitoring of the Second Mode Internal Solitary Wave near Dongsha Atoll

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