SUMMARY

Linear arrays are usually deployed for passive surface-wave investigations because of their high efficiency and convenience. In populated urban areas, it is almost impossible to set up a 2-D array in terms of the restriction from the existing infrastructures. The limited azimuthal coverage, however, lacks the ability to attenuate velocity overestimation caused by directional noise sources. We came up with a novel idea to compensate the azimuthal coverage by adding two more offline receivers to a conventional linear array, which is called pseudo-linear-array analysis of passive surface waves (PLAS). We used a beamforming algorithm to capture noise sources distribution and extract accurate dispersion curves. We used array response function to explain the superiority of the pseudo-linear array over the linear array and present the basic workflow of PLAS. Synthetic tests and field examples demonstrated the feasibility of PLAS to measure unbiased dispersion image. Comparison with mostly used passive surface wave methods (refraction microtremor, multichannel analysis of passive surface waves, spatial autocorrelation method, frequency–wavenumber analysis) suggested that PLAS can serve as an alternative passive surface wave method, especially in urban areas with restricted land accessibility and short-time acquisition demands.

中文翻译：

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基于波束形成的无源表面波伪线性阵列分析

概要

线性阵列由于其高效和方便而通常被部署用于被动表面波研究。在人口稠密的城市地区，就现有基础设施的限制而言，几乎不可能建立二维阵列。但是，有限的方位角覆盖范围不足以减弱由方向性噪声源引起的速度过高估计的能力。我们提出了一种新颖的想法，可以通过向传统的线性阵列中添加两个以上的脱机接收器来补偿方位角覆盖，这称为无源表面波的伪线性阵列分析（PLAS）。我们使用波束成形算法来捕获噪声源分布并提取准确的色散曲线。我们使用数组响应函数来解释伪线性数组相对于线性数组的优越性，并介绍了PLAS的基本工作流程。综合测试和现场实例证明了PLAS测量无偏色散图像的可行性。与最常用的无源表面波方法（折射微震，无源表面波的多通道分析，空间自相关方法，频率-波数分析）的比较表明，PLA可以用作替代的无源表面波方法，尤其是在土地可及性受限和短时采集需求。