We consider the effects of oblique incidence of a wave on the creation of a 3-D image of a planar interface with an array-type directional borehole radar. In this study, we focus on the situation where the radar probe is close to the planar interface. In such circumstances, the reflected wave from the planar interface may be incident on the receiving array antenna at very steep elevation angles. As a result, borehole effects cause differences in the arrival times of the wave at the array elements, and consequently some errors emerge in imaging the planar interface. Observing the arrival time differences, we present an algorithm to compensate those errors in creating a 3-D image of a planar interface. Computer simulations predict that the errors may occur when the circular dipole array antenna is in an air-filled borehole in rock. Numerical simulations show that our proposed algorithm generates a 3-D image of an interface around an exact position, whereas conventional methods produce some spurious images opposite to the correct position (i.e., out of position by 180°). We then applied the proposed method to analyze reflected waves from a real-world fault in rock. A 3-D image of the fault could be successfully created, which was not possible using the conventional method.

中文翻译：

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充气钻孔中圆形偶极子阵列平面界面 3D 成像中斜入射的考虑


我们考虑了波的倾斜入射对使用阵列型定向钻孔雷达创建平面界面 3D 图像的影响。在本研究中，我们重点研究雷达探头靠近平面界面的情况。在这种情况下，来自平面界面的反射波可能以非常陡的仰角入射到接收阵列天线上。结果，钻孔效应导致波到达阵列单元的时间存在差异，从而在平面界面成像中出现一些误差。通过观察到达时间差异，我们提出了一种算法来补偿创建平面界面 3D 图像时的这些误差。计算机模拟预测，当圆形偶极子阵列天线位于岩石中充满空气的钻孔中时，可能会出现错误。数值模拟表明，我们提出的算法会生成精确位置周围界面的 3D 图像，而传统方法会生成一些与正确位置相反的虚假图像（即偏离位置 180°）。然后，我们应用所提出的方法来分析来自真实世界岩石断层的反射波。可以成功创建故障的 3D 图像，这是使用传统方法无法实现的。