Drone-based electromagnetic survey system for environmental applications

During the last few years, the number of applications utilizing unoccupied aerial vehicles (UAVs), or drones, has increased rapidly in geophysics. The main benefits of airborne surveys are the ability to avoid terrain obstacles such as lakes, rivers, swamps, and ravines and the ability to collect evenly sampled data over large areas quickly. Drone surveys are safer and more cost-effective than ground surveys, especially in rough terrain. Compared to manned aircrafts, drones are cheaper to acquire and to operate. Drones are also versatile, fast to deploy, and ecologically more friendly.

Presently, drones are commonly used for magnetic surveying, and in addition to normal photogrammetry, drones are also used for multispectral and thermal imaging. Electromagnetic (EM), radiometric and gravity applications have been scarce, because the instruments are heavy compared to the modest payload of reasonable priced drones. Special adaptation or completely new instrumentation is needed to enable more drone applications.

Radai is a private Finnish company specialized in drone-based geophysical and environmental surveys. For the last five years Radai have been developing Louhi – a frequency-domain electro­magnetic (EM) system that is lightweight enough to be operated by drones. Presently, Louhi is operated using a large (Ø 100 m) ground loop as the EM source and a standalone 3-component EM receiver is towed by a VTOL (vertical take-off and landing) drone. Radai also develops a fully airborne system where a smaller transmitter loop (Ø 1 m) is fixed to the drone and receiver is towed either by the same drone or by a second drone that flies in tandem with the first one. The applications of the new EM system include geological mapping, mineral exploration, groundwater and geotechnical investigations and environmental monitoring. This paper gives details of the drone-based Louhi EM system and shows results from the first environmental survey made over a tailings pond dam of closed Pyhäsalmi Zn-Cu mine in Finland. The work is made as a part of EU Horizon 2020 funded Goldeneye project.