Abstract Two-dimensional (2D) electrical resistivity tomography (ERT) surveying systems typically use standard protocols that assume straight survey lines and collinear electrodes. However, due to the presence of infrastructures and other surface constraints, it is not always possible to conduct 2D ERT surveys along straight lines. When survey lines are angled, the apparent resistivity data are affected for measurements where electrodes occur on either side of the position of the angle, since the assumed distances between some of the electrodes are larger than the true distances. This study investigates the impact of angled survey lines on 2D ERT data and inverse resistivity models for the Wenner (α) array. Theoretical considerations show that measurements along angled survey line are sensitive to resistivity changes at position laterally displaced from the survey line, while both the calculated apparent resistivities and the depths of investigation are affected when electrodes straddle the angle. The resulting errors are, however, small. Even for a large angle of 45°, the errors are smaller than 6.5% for the affected apparent resistivity measurements, and smaller than 3.8% for the median depths. Since the apparent resistivity data and the pseudo-depths are affected by angles in the survey lines, the inverse resistivity models are also affected. Numerical modelling shows that even small input errors may be propagated (both in magnitude and spatially) during inversion, thereby distorting the resulting resistivity models. The distorted inverse resistivity models could lead to the incorrect interpretation of the locations, geometries and orientations of subsurface structures, which could lead to poorly sited production boreholes. The results of field surveys show that apparent resistivity data sets recorded along angled lines may be partially corrected by calculating the true geometric factors and by adjusting the apparent resistivity data accordingly. Significantly improved inverse resistivity models are found for corrected data sets.

中文翻译：

---

倾斜测量线对使用 Wenner (α) 阵列的 2D ERT 测量的影响以及对 Karoo 岩石地下水勘探的影响

摘要 二维 (2D) 电阻率断层扫描 (ERT) 测量系统通常使用标准协议，假设测量线为直线和共线电极。然而，由于基础设施和其他地表限制的存在，并不总是可以沿着直线进行 2D ERT 勘测。当测线成角度时，由于某些电极之间的假定距离大于真实距离，因此对于电极出现在角度位置两侧的测量，视电阻率数据会受到影响。本研究调查倾斜测量线对温纳 (α) 阵列的二维 ERT 数据和反电阻率模型的影响。理论考虑表明，沿倾斜测量线的测量对从测量线横向位移的位置处的电阻率变化敏感，而当电极跨越该角度时，计算的视电阻率和调查深度都会受到影响。然而，由此产生的误差很小。即使对于 45° 的大角度，受影响的视电阻率测量的误差也小于 6.5%，中值深度的误差小于 3.8%。由于视电阻率数据和伪深度受测线角度的影响，反电阻率模型也受到影响。数值模拟表明，即使是很小的输入误差也可能在反演过程中传播（在幅度和空间上），从而扭曲所得电阻率模型。扭曲的逆电阻率模型可能导致对地下结构的位置、几何形状和方向的错误解释，这可能导致生产钻孔位置不佳。实地调查的结果表明，通过计算真实的几何因素并相应地调整视电阻率数据，可以部分校正沿倾斜线记录的视电阻率数据集。对于校正数据集，发现了显着改进的逆电阻率模型。实地调查的结果表明，通过计算真实的几何因素并相应地调整视电阻率数据，可以部分校正沿倾斜线记录的视电阻率数据集。对于校正数据集，发现了显着改进的逆电阻率模型。实地调查的结果表明，通过计算真实的几何因素并相应地调整视电阻率数据，可以部分校正沿倾斜线记录的视电阻率数据集。对于校正数据集，发现了显着改进的逆电阻率模型。