Experiments on magnetic interference for a portable airborne magnetometry system using a hybrid unmanned aerial vehicle (UAV)

Airborne magnetic surveys are an important and efficient tool for mapping the subsurface, providing insights e.g. into mineral deposits. Compared to traditional ground methods, airborne magnetic surveys offer great advantages with improved access and rapid sampling. But the cost and hassle of transporting and operating a conventional manned airborne magnetic survey system are strong impediments for its wider use. In addition, the conventional airborne systems are challenged by the need for low-altitude (≤ 80 m) surveying to detect small-scale subsurface features evident in ground surveys. Portable and compact airborne magnetic survey systems using unmanned aerial vehicles (UAVs) can not only bridge the gap between conventional airborne magnetic surveys and ground magnetic surveys but also complement magnetic surveys to fit broader geophysical applications. Therefore, developing high-quality, stable, and portable UAV-borne survey systems is of high interest to the geophysical exploration community. However, developing such a system is challenging owing to strong magnetic interference introduced by onboard electric engines and other onboard electronic devices. As a result, tests concerning the static and dynamic magnetic interference of a UAV are critical to assess the severity of the interference and can help to improve the design of the system at the early stage of development. A static experiment and two dynamic experiments were conducted to understand the characterization of the magnetic interference of our hybrid vertical take-off and landing (VTOL) UAV. The results of the static experiment show that the wing area is highly magnetic due to the proximity to servomotors and motors, but the area along the longitudinal axis of the UAV is relatively magnetically quiet. To reduce the magnetic signature, the highly-magnetic servomotors on the wings were replaced with less magnetic servomotors of a brush-less type. Assisted by aerodynamic simulations, we further designed a front-mounting solution for two compact magnetometers. Two dynamic experiments were conducted with this setup to understand the dynamic interference of the UAV in operation. The results of the dynamic experiments reveal that the strongest source of in-flight magnetic interference is mainly due to the cables connecting the battery to the flight controller and that this effect is most influential during pitch maneuvers of the aircraft.

Finding the Gaps in America’s Magnetic Maps

A 2017 executive order mandated a plan to evaluate U.S. access to critical mineral resources, but the airborne magnetic survey maps that support this effort are sadly out of date.

REPORT OF THE SEG COMMITTEE FOR A NATIONAL MAGNETIC ANOMALY MAP

Our country’s urgent need to find new sources for minerals and energy and its need to know more about the planet on which we live could be greatly assisted by preparation of a national magnetic anomaly map (NMAM)—a map which will provide an accurate representation of the earth’s anomalous magnetic field. It is startling to note that the U.S. is one of the few developed countries which has not commissioned a detailed airborne magnetic survey of the whole country, followed by production of a national magnetic anomaly map.

Airborne geophysical survey in central East Greenland

In 1971 aeroradiometric work was carried out in the Scoresby Sund region (see Nielsen, 1972; LØvborg & Nielsen, 1973). In 1973 an airborne geophysical programme was begun in East Greenland between 72° and 76°N. The main topics of this programme were a regional radiometric reconnaissance coupled with an airborne magnetic survey. The greatest importance was attached to the radiometric project, which is a collaboration between GGU and the Danish Atomic Energy Commission's Research Establishment, Risø.