An early time semi-airborne loop source TEM system

We present a new semi-airborne transient electromagnetic (TEM) system, dTEM, for subsurface imaging. The dTEM system is designed for both imaging of groundwater and mineral resources. The system uses a large ground loop for transmitting energy into the ground. It's a dual moment system with peak current up to 30A for high moment and 1-2A for low moment. The fast LM turn off time is around 8s from the beginning of the turn-off ramp. The receiver coil is a high frequency, low noise, open air coil carried by the drone as a slung load. The high accuracy synchronisation between the transmitter and the receiver is achieved by GPS, within less than 50ns. The drone is equipped with two lasers for determination of the attitude and real-time image processing has been developed to measure and control the movement of the receiver coil with the drone in the airspace. Data from all sensors are continuously streamed to the ground station. The system can be used for mapping of deep targets. However, as the current waveform and system bandwidth is well defined also more shallow layered targets can be mapped. The latter makes it possible to use the system to map shallow ground water aquifers in terrains inaccessible for traditional ground-based TEM systems.