Use of different flight configurations in a drone magnetometric system

Over the past decade, the miniaturization of geophysical instruments, such as magnetometers, has recently opened new opportunities to install them on-board drones. Unmanned Aerial Vehicle (UAV) are becoming a desirable alternative or a complementary approach for remote sensing since they allow a high versatility and flexibility in comparison to traditional airborne systems or ground surveys. Magnetic sensors mounted on drones allow carrying out surveys with intermediate characteristics between traditional aero magnetism and ground surveys in terms of resolution, extension of the investigation area, elevation, and speed. One of the main problems related to the UAV-magnetometer system is the characterization and compensation of electromagnetic interference generated by the mobile platform. Most of the studies have concluded that the minimum distance to be maintained between the sensors and the mobile platform to avoid interference is 3 m. However, this strategy may compromise the stability of the system or create unwanted oscillations of the sensors that have the potential to introduce periodic variations in the data. In this study, magnetic measurements have been made over buried metal objects (probably pipelines and cables) whose position was unknown. Two different surveys were conducted using a multirotor UAV and a miniature cesium vapor atomic magnetometer (MFAM, Geometrics). During the first test, the magnetometer was fixed to the drone landing gear, at only 0.6 m distance between the rotors and the magnetometer; in the second investigation test, sensors were suspended through ropes 3 m below the platform. Spectral analysis shows that the target signal and the interference generated by the platform do not spectrally overlap, even when the distance between the drone and the sensors is minimal. The anomalies identified in UAV magnetic maps are comparable in terms of amplitude with those shown by a magnetic ground survey carried out in the same investigation area. Finally, the sources identified through modelling of the aerial surveys data are comparable in terms of position and depth with those located by the ground magnetic data. These results demonstrate the high quality of the drone-borne data acquired in the two flight configurations. Overall, this study shows the feasibility of different UAV-magnetometer flight configurations that may be chosen in function on the survey target and the flight conditions.