Accessing the diffracted wavefield by coherent subtraction
Accessing the diffracted wavefield by coherent subtraction
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DOI：
10.1093/gji/ggx291
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发表时间：
2017-10
影响因子：
2.8
通讯作者：
B. Schwarz;D. Gajewski
中科院分区：
文献类型：
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作者：
B. Schwarz;D. Gajewski
衍射具有独特的性质，在通常的实践中仍然很少被利用。除了包含关于散射几何形状的亚波长信息或指示小尺度结构复杂性之外，与反射相比，它们提供上级照明。虽然衍射可以在所有尺度和大多数现实介质中发生，但相应的特征通常具有较低的振幅，并且可能被更突出的波场分量所掩盖。人们广泛观察到，自动叠加起到了方向滤波器的作用，有利于获得最相干的波至。与其他作品相比，通常旨在将求和算子转向较弱的贡献，我们利用这种方向选择来相干地近似最主要的到达，并从数据中减去它们。在叠加过程中获得的波前属性可以导出额外的滤波器函数的支持下，该策略可以完全由数据驱动恢复微弱的衍射背景波场，并使其可用于进一步处理。大的源-接收器偏移采集提供了高数据冗余和改善照明的贝内。然而，大偏移距记录的获取成本通常很高，大多数学术研究都面临着极低的通道数和明显超过可用偏移距范围的目标深度。在圣托里尼岛附近的爱琴海记录的复杂单通道场数据示例表明，衍射背景波场非常丰富，尽管没有高通道数，仍然可以检测和表征，这表明在工业和学术界有各种应用。
SUMMARY Diffractions have unique properties which are still rarely exploited in common practice. Aside from containing sub-wavelength information on the scattering geometry or indicating small-scale structural complexity, they provide superior illumination compared to reflections. While diffraction occurs arguably on all scales and in most realistic media, the respective signatures typically have low amplitudes and are likely to be masked by more prominent wavefield components. It has been widely observed that automated stacking acts as a directional filter fa-voring the most coherent arrivals. In contrast to other works, which commonly aim at steering the summation operator towards fainter contributions, we utilize this directional selection to coherently approximate the most dominant arrivals and subtract them from the data. Supported by additional filter functions which can be derived from wavefront attributes gained during the stacking procedure, this strategy allows for a fully data-driven recovery of the faint diffracted background wavefield and makes it accessible for further processing. Large source-receiver offset acquisition offers the benefits of high data redundancy and improved illumination. How-ever, large-offset recordings are generally expensive to acquire and the majority of academic research is confronted with a comparably low channel count and target depths that significantly exceed the available offset range. A complex single-channel field data example recorded in the Aegean sea near Santorini illustrates that the diffracted background wavefield is surprisingly rich and despite the absence of a high channel count can still be detected and characterized, suggesting a variety of applications in industry and academia.