# Electromagnetic Field Distribution and Data Characteristics of SUTEM of Multilayer Aquifers
## 5 Conclusions  
First, we derived the electromagnetic field expression at any position for a rectangular emission source located in any layer of the region of interest. This region can be transformed into a half-space expression by changing the resistivity of the layer above the emission return line to realize the one-dimensional forward evolution of the SUTEM, and the ensuing calculation accuracy meets the application requirements. Subsequently, we used the written forward simulation program to study the transient electromagnetic field diffusion in the time domains of uniform half-space and single-aquifer and double-aquifer models. We further used the data characteristics of SUTEM and analyzed the influence of shallow aquifer changes on the ability of each measurement point to detect deep aquifers. The following conclusions are drawn:  
* When the receiving point is located above the probe target layer and does not touch the target layer, the initial influence (relative rate of change) of the target layer on the receiving point is 0 and is stable for a certain period of time. With increasing time, the influence of the target layer on the receiving point above it increases negatively and then increases positively, before gradually decreasing. * When the receiving point is located at the top interface of the target layer, the initial influence (relative rate of change) of the target layer is negative, and it remains stable for a certain period of time. With an increase in time, the influence of the target layer on it increases positively and then gradually decreases. * When the receiving point is located at the bottom interface of the target layer and below, the initial impact (relative rate of change) of the target layer on it is approximately \(-100\%\) and remains stable for a certain period of time. With increasing time, the impact of the target layer on it increases positively and then gradually decreases. * The influence of the shallow aquifer on the surface measurement point is relatively large, and the influence on the measurement point below the deep aquifer is relatively  
Figure 20: Influence of shallow aquifer depth, thickness, and resistivity changing simultaneously on the ability of the TEM to detect deep aquifers. small. The change in the resistivity of the shallow aquifer shows the greatest impact on the detection ability of the deep aquifer at each measurement point, the thickness change shows the second largest effect on the detection ability of each measurement point, and depth change shows the smallest effect on the detection capability of each measurement point. * Compared with the commonly used nuclear magnetic resonance technology for groundwater detection, the SUTEM studied in this paper has a greater detection depth. It can be seen from the above research that when the receiving point is located underground, the received data will contain more geological information of the deep aquifer, such that successful interpretation of the data will improve the detection performance of the transient electromagnetic method. In fact, a deep receiving point has always been affected by an overlying aquifer, and longitudinal positioning capability is relatively weak. To solve these problems and improve the detection accuracy of TEM in coal mine water control and prevention, our future work will consider joint inversion interpretation research of ground TEM and SUTEM data. Conceptualization, M.L. and Z.J. ; methodology, M.L. ; software, X.T. ; formal analysis, M.L. ; resources, M.L. ; data curation, M.L. ; writing--original draft preparation, M.L. ; writing--review and editing, S.L. ; supervision, Z.J. and S.C. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (No. 42204139 and No. 42274179) and the Key Projects of National Natural Science Foundation of China (No. 42230811). The data presented in this study are available on request from the corresponding author. The data are not publicly available.