A drone-based electromagnetic system allows to efficiently map large areas and to generate three-dimensional conductivity models of the subsurface. The used semi-airborne method that has been developed in the DESMEX project can provide large penetration depths and higher lateral resolution compared to classical helicopter-borne electromagnetics.
The measured is described by the term semi-airborne electromagnetics: A towed sensor records three-component magnetic fields in the air. Different from classical airborne surveys, the source is not dragged, but realized on the ground in form of a grounded dipole (current I in red). The associated (primary) magnetic field (B in blue) induces induction currents (J in red) in conducting subsurface structures which do in turn generate a (secondary) magnetic field (Bs in blue), which is used to reconstruct the three-dimensional conductivity distribution in the subsurface. Due to the stronger source and the larger offsets between transmitter and receiver one can achieve larger investigation depths of up to 1km. This method was developed in the project DESMEX and is applied in the follow-up projects (DEXMEX II und DESMEXreal).
Alternatively to logistically laborious helicopter, we increasingly drones that are more mobile and provide a higher degree of detail due to the lower speed of flight. Beyond mineral deposits we focus as well on saline aquifers in Northern Germeny. Specifc difficulties are the electromagnetic drone noise, but also data at high penetration depths.
Stoll et al. (2020) describes the system consisting of an octocopters X825 along with dedicated sensors: The magnetic fields are measured by an induction coil (Metronix SHFT02e) and a fluxgate magnetometer (Bartington) mounted on a pendulum and recoreded by an ADU08e datalogger (Metronix). Attitudes are measured using an inertial measurement unit (IMU) of XSens.