A comparison of TEM data from different near-source systems

Abstract

Loop-source transient electromagnetic (TEM) is one of the most popular near-source TEM systems with wide applications, such as the traditional approach of prospecting metalliferous and hydrogeological targets in the subsurface. Recent efforts have been focused on the implementation of short-offset grounded-wire TEM (SOTEM), which is a newly proposed and more helpful technique for performing near-source TEM surveys. However, configurations for applying near-source TEM are complicated and have not been well investigated and tested; therefore no applicable principles can be followed and recommended for optimizing near-source TEM configuration for anomaly detection. To resolve such limitations, this study conducts a comparison of the vertical magnetic field or the electric field generated from various near-source TEM systems regarding the characteristics of their response distribution, investigation depth, as well as sensitivity to geo-electric structure, through both forward modeling and a field survey in China. It is concluded that the electric field from SOTEM has a better detection capability to resistive anomaly and higher sensitivity to the resistivity of anomaly, while the vertical magnetic fields from SOTEM and loop TEM have better detection capability to conductive anomaly and higher sensitivity to the thickness of an anomaly. From the view of detection depth, the SOTEM system performs better than the loop-TEM system, and the electric field demonstrates an even larger detection depth than the vertical magnetic field in the same SOTEM survey for commonly used parameters.