Research on the application of a 3-m transmitter loop for TEM surveys in mountainous areas

Large loop transient electromagnetic (TEM) is a widely used surface exploration method for mapping electrically conductive bodies. However, when working in the mountainous areas of China, it is difficult to lay out large enough transmitter loops for conventional surveys. An option for this type of terrain is a newly designed TEM survey configuration that uses a small 3-m square loop in combination with a high current (1,000 A to 2,000 A) TEM transmitter to excite a powerful EM field for detecting targets at greater depths. The detection depth of the system is analyzed. After comparing the responses as well as the detection depths between this special system and standard large loop configurations, it is shown that: 1) a small loop system can result in a detection depth similar to that of a large loop system} and 2) a small loop system is superior to a large loop during shallow depth target detection as well as in mountainous areas. Sufficient signal intensity can be obtained by a small central loop configuration equipped with a high current transmitter and a large equivalent area receiver coil. A large trial survey was conducted on the surface of mountainous areas in the Shanxi Province of China. This TEM survey showed that the 3-m by 3-m transmitter loop system was an effective method for deep TEM sounding in mountainous areas.