Brooks Laura A, Gerstoft Peter
Marine Physical Laboratory, Scripps Institution of Oceanography, La Jolla, California 92093, USA.
J Acoust Soc Am. 2009 Feb;125(2):723-34. doi: 10.1121/1.3056563.
Approximation of Green's functions through cross-correlation of acoustic signals in the ocean, a method referred to as ocean acoustic interferometry, is potentially useful for estimating parameters in the ocean environment. Travel times of the main propagation paths between hydrophone pairs were estimated from interferometry of ocean noise data that were collected on three L-shaped arrays off the New Jersey coast while Tropical Storm Ernesto passed nearby. Examination of the individual noise spectra and their mutual coherence reveals that the coherently propagating noise is dominated by signals of less than 100 Hz. Several time and frequency noise normalization techniques were applied to the low frequency data in order to determine the effectiveness of each technique for ocean acoustic applications. Travel times corresponding to the envelope peaks of the noise cross-correlation time derivatives of data were extracted from all three arrays, and are shown to be in agreement with the expected direct, surface-reflected, and surface-bottom-reflected interarray hydrophone travel times. The extracted Green's function depends on the propagating noise. The Green's function paths that propagate horizontally are extracted from long distance shipping noise, and during the storm the more vertical paths are extracted from breaking waves.
通过海洋中声信号的互相关来近似格林函数，这种方法被称为海洋声学干涉测量法，它在估计海洋环境参数方面可能很有用。水听器对之间主要传播路径的传播时间是根据在热带风暴欧内斯托在新泽西海岸附近经过时，在新泽西海岸外的三个L形阵列上收集的海洋噪声数据的干涉测量法估算出来的。对各个噪声谱及其相互相干性的检查表明，相干传播的噪声主要由频率低于100赫兹的信号主导。为了确定每种技术在海洋声学应用中的有效性，对低频数据应用了几种时间和频率噪声归一化技术。从所有三个阵列中提取了与数据的噪声互相关时间导数的包络峰值相对应的传播时间，结果表明这些传播时间与预期的直接、表面反射和表面-底部反射的阵列间水听器传播时间一致。提取的格林函数取决于传播的噪声。水平传播的格林函数路径是从远距离航运噪声中提取的，而在风暴期间，更垂直的路径是从破浪中提取的。
