In this study, a recently developed time-domain electromagnetic method called the short-offset grounded-wire transient electromagnetic (SOTEM) method, which is a near-source observation method, was adopted to obtain strong signals and great detection depths. The responses of the SOTEM and long-offset transient electromagnetic (LOTEM) methods were compared to further guide and promote the SOTEM method. Currently, the comparison between SOTEM and LOTEM methods is primarily based on one-dimensional (1D) models. However, most geological bodies are three-dimensional (3D) structures. We investigated the responses of a grounded-wire transient electromagnetic method based on 3D models using the 3D finite-difference time-domain method. In addition, the signal strengths, detection sensitivities and detection depths of the SOTEM and LOTEM methods were compared. The results revealed that the field amplitudes of E_x (electrical component parallel to the transmitting source) and ∂B_y/∂t (magnetic component perpendicular to the transmitting source horizontally) were higher at the short offsets than at the long offsets. For the ∂B_x/∂t (magnetic component parallel to the transmitting source) and the vertical magnetic component ∂B_z/∂t, at initial times, the responses received would be stronger when closer to the transmitting source, whereas at later times, the responses would be stronger when farther from the source. E_x detection sensitivity increased with an increase in the offset at initial times, and increased with a decrease in the offset at later times. The detection sensitivities of the three magnetic field components at short offsets were higher than those at long offsets. The ∂B_y/∂t effective detection depth was the greatest. Generally, the effective detection depths of the three magnetic field components increased with decreasing offset. The range of the ratio of the horizontal distance, r, between the transmitting source and the target body to the effective detection depth H was 0.5-1.1.

在这项研究中，采用了一种新近发展的时域电磁方法，称为短偏移接地线瞬变电磁（SOTEM）方法，它是一种近源观测方法，能够获得强信号和大探测深度。比较SOTEM和长偏移瞬变电磁（LOTEM）方法的响应，以进一步指导和推广SOTEM方法。目前，SOTEM 和 LOTEM 方法之间的比较主要基于一维（1D）模型。然而，大多数地质体都是三维 (3D) 结构。我们使用 3D 时域有限差分法研究了基于 3D 模型的接地线瞬态电磁方法的响应。另外，信号强度，比较了SOTEM和LOTEM方法的检测灵敏度和检测深度。结果表明，场振幅Ex（平行于发射源的电分量）和∂B _y /∂t（垂直于水平发射源的磁分量）在短偏移处比在长偏移处更高_。对于∂B _x /∂t（平行于发射源的磁分量）和垂直磁分量∂B _z /∂t，在初始时刻，靠近发射源时接收到的响应会更强，而在后期，当远离源时响应会更强。埃克斯_{_}初始时检测灵敏度随着偏移量的增加而增加，并且在后期随着偏移量的减小而增加。短偏移距下三个磁场分量的检测灵敏度均高于长偏移距下的检测灵敏度。∂B _y /∂t有效检测深度最大。一般来说，三个磁场分量的有效检测深度随着偏移量的减小而增加。发射源与目标体之间的水平距离r与有效探测深度H的比值范围为0.5～1.1。