SATEM: A new drone-based semi-airborne transient electromagnetic receiver system

Semi-airborne Transient Electromagnetic method (SATEM) stands as a pivotal tool for subsurface mineral resources exploration, geological survey, and groundwater investigation in complex terrains. This study develops a bespoke SATEM receiver system tailored for such explorations, comprising a lightweight recorder and small-size receiving coil. The recorder employs a dual microprogrammed control unit (MCU) hierarchical structure framework, facilitating seamless SATEM data acquisition and storage. Meanwhile, the receiving coil, featuring a shield and multi-turn loop, integrates an embedded signal acquisition module capable of storing electromagnetic signals alongside Global Navigation Satellite System (GNSS), acceleration, and altitude data. Time synchronization between receiver and transmitter relies on the pulse per second (PPS) signal from GNSS, so it can work with any transmitter systems equipped with GNSS based synchronization. The low internal noise of the receiver system is about 0.834 μV and it has a high sampling rate of 256 kbps. We carried out a geophysical survey using the developed SATEM receiver system in Zhaiya Tunnel in Guangxi, China, where the topographical relief is significant and geological data are scarce. The SATEM system detected subsurface karst development area around the tunnel site, providing critical information ahead of tunnel construction. The results are in good agreement with the true karst revealed during the tunnel excavation.