Reliable acoustic path (RAP) is a direct path used for sound propagation between a shallow source and a deep receiver in deep water. The RAP environment can provide a high signal-to-noise ratio (SNR) environment for source localization, so it has been widely studied for underwater passive detection. Active detection can be used for source localization during the descent of a vertical line array (VLA). However, the flow noise originating from the pressure fluctuations in the turbulent boundary layer (TBL) during the descent degrades the detection performance of the VLA. This paper presents a calculation of the response of the cylindrical hydrophones to axisymmetric turbulent wall pressure and the physical properties of flow noise. The flow noise was calculated using the wavenumber-frequency spectrum analysis method, which is based on Carpenter’s TBL pressure spectrum. The results show that the energy of the flow noise is concentrated mainly in low frequencies and it increases and spreads toward high frequencies with increasing stream velocity. The conclusions have been verified with experimental data. In addition, the noise correlation between two hydrophones will undergo oscillatory decay as the hydrophone spacing increases. The above findings will be beneficial for signal processing of an active sonar array.

中文翻译：

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深水下降过程中垂直线阵的流噪声频谱分析

可靠声学路径 (RAP) 是用于在深水中的浅声源和深接收器之间进行声音传播的直接路径。RAP环境可以为源定位提供高信噪比（SNR）的环境，因此被广泛研究用于水下无源检测。主动检测可用于垂直线阵列 (VLA) 下降期间的源定位。然而，下降过程中湍流边界层（TBL）中的压力波动引起的流动噪声降低了VLA的检测性能。本文介绍了圆柱水听器对轴对称湍流壁压力的响应和流动噪声物理特性的计算。使用波数频谱分析方法计算流动噪声，这是基于 Carpenter 的 TBL 压力谱。结果表明，流动噪声的能量主要集中在低频，随着水流速度的增加，它会增加并向高频扩散。结论已通过实验数据得到验证。此外，随着水听器间距的增加，两个水听器之间的噪声相关性会发生振荡衰减。上述发现将有利于有源声纳阵列的信号处理。随着水听器间距的增加，两个水听器之间的噪声相关性将发生振荡衰减。上述发现将有利于有源声纳阵列的信号处理。随着水听器间距的增加，两个水听器之间的噪声相关性将发生振荡衰减。上述发现将有利于有源声纳阵列的信号处理。