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直接从时间域出发 ,应用时域有限差分方法 (FDTD)分析地下和地面的瞬变响应。由于二维情况便于图形表示 ,采取了线源二维地电模型。通过对二层均匀地电结构和含二维低阻体时地面垂直感生电动势曲线的计算 ,说明瞬变场响应有滞后现象 ,即异常地质体一旦引起瞬变响应 ,就会往后延时 ,并使响应延续较长时间。在实际的工程勘察中 ,曾用 3～ 5ms以后的延迟时间探测过较浅的异常体 ,如 2 0m至 150m深度范围内的地下老窑采空区 ,并取得了较好的探测效果 ,上述数字模拟结果为以往的实践提供了理论依据。
Starting directly from the time domain, the transient responses of the ground and the ground are analyzed using the finite-difference time-domain method (FDTD). Since the two-dimensional situation is convenient for the graphical representation, a two-dimensional geoelectric source model is adopted. Through the calculation of the vertical induced electromotive force (EMF) curve of the ground when the second-level uniform electric structure and the two-dimensional low-resistance body are included, it shows that there is a hysteresis in the transient response. That is to say, once the abnormal geological body causes the transient response, , And the response lasted longer. In the actual engineering survey, shallow anomalies such as shallow old gobs in the depth range of 2 0m to 150m have been detected with delay time of 3 ~ 5ms, and good detection results have been obtained. The numerical simulation results provide the theoretical basis for the past practice.