Study on the Placement Location of the Infinite Pole of an ERT Pole-Dipole Array

Among the common arrays of electrical resistivity tomography, the pole-dipole array is widely used due to its unique advantages such as more apparent resistivity information in the measured profile and the ability to realize advanced detection. However, this array requires an infinite pole, and there is still no uniform standard on the least amount of distance from the survey line that can be regarded as infinity, which is crucial in some space-limited measurement environments. Therefore, in this study, the geometric factor K of the pole-dipole array and quadrupole array is analyzed first, and the root mean square error rate (RMSE%) between different geometric factors is calculated. Then the threshold is set to 5% to determine the theoretical infinite pole minimum multiple \([m]_{t} = 2\) ${[m]}_t=2$ . With the premise that the survey line length is L and the distance between the infinite pole and the starting electrode of the survey line is m*L, when the survey line length multiple is \(m \ge [m]_{t} = 2\) $m\ge {[m]}_t=2$ , the influence of the infinite pole on the measured data can be ignored in engineering. Finally, verification experiments are carried out in different environments with anomalous bodies of different properties as test objects, and it is proved that the theoretical value \([m]_{t} = 2\) ${[m]}_t=2$ is applicable to various modes of pole-dipole array and tested objects with different properties.