Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
Noiselab, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0238, USA.
J Acoust Soc Am. 2020 Dec;148(6):3836. doi: 10.1121/10.0002926.
The Green's function retrieval in media with horizontal boundaries usually only considers the extraction of direct and reflected waves but ignores the virtual head waves, which have been observed experimentally from ocean ambient noise and used to invert for geometric and environmental parameters. This paper derives the extraction of virtual head waves from ocean ambient noise using a vertically spaced sensor pair in a Pekeris waveguide. Ocean ambient noise in the water column is a superposition of direct, reflected, and head waves. The virtual head waves are produced by the cross-correlations between head waves and either reflected waves or other head waves. The locations of sources that contribute to the virtual head waves are derived based on the method of stationary phase. It is the integration over time of contributions from these sources that makes the virtual head waves observable. The estimation of seabed sound speed with virtual head waves using a vertical line array is also demonstrated. The slope of the virtual head waves is different from that of direct and reflected waves in the virtual source gather; it is therefore possible to constructively stack the virtual head waves. The predictions are verified with simulations.
在具有水平边界的介质中，格林函数的反演通常只考虑直达波和反射波的提取，而忽略了虚拟首波，这些波已经从海洋环境噪声中观测到，并被用于反演几何和环境参数。本文推导了利用 Pekeris 波导中垂直间隔传感器对从海洋环境噪声中提取虚拟首波的方法。水柱中的海洋环境噪声是直达波、反射波和首波的叠加。虚拟首波是由首波与反射波或其他首波的互相关产生的。根据定相法可以推导出对虚拟首波有贡献的声源的位置。正是这些声源的时间积分使得虚拟首波可以被观测到。本文还演示了利用垂直线列对虚拟首波进行海底声速估计。虚拟源汇聚中的虚拟首波斜率与直达波和反射波不同；因此，可以对虚拟首波进行建设性地叠加。预测结果与模拟结果进行了验证。
