Marine Physical Laboratory, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0238, USA.
J Acoust Soc Am. 2012 Feb;131(2):1079-86. doi: 10.1121/1.3676700.
Ambient acoustic noise fields in the ocean are generally three dimensional in that they exhibit vertical and horizontal directivity. A model of spatially homogeneous noise is introduced in which the directionality is treated as separable, that is, the overall directionality of the field is the product of the individual directivities in the horizontal and vertical. A uni-modal von Mises circular distribution from directional statistics is taken to represent the noise in the horizontal, whilst the vertical component is consistent with a surface distribution of vertical dipoles. An analysis of the coherence and cross correlation of the noise at two horizontally aligned sensors is developed. The coherence function involves a single integral over finite limits, whilst the cross-correlation function, derived on the assumption that the noise has been pre-whitened, is given by an integral with limits that depend on the correlation delay time. Although the cross-correlation function does not exhibit delta functions that could be identified with the Green's function for propagation between the two sensors in the field, it does drop abruptly to zero at numerical time delays equal to the travel time between the sensors. Hence the noise could be used to recover the sound speed in the medium.
海洋中的环境噪声场通常是三维的，因为它们表现出垂直和水平指向性。本文介绍了一种空间均匀噪声模型，其中方向性被视为可分离的，即场的整体方向性是水平和垂直方向上的各向异性的乘积。从方向统计学中采用单峰冯·米塞斯圆形分布来表示水平方向上的噪声，而垂直分量与垂直偶极子的表面分布一致。对两个水平对准的传感器处噪声的相干性和互相关进行了分析。相干函数仅涉及有限极限的单个积分，而互相关函数则是基于噪声已白化的假设推导出来的，其积分的极限取决于相关延迟时间。尽管互相关函数没有可以与场中两个传感器之间传播的格林函数对应的冲激函数，但它确实在数值延迟时间等于传感器之间的传播时间时突然降为零。因此，噪声可用于恢复介质中的声速。
