Technical reports about drone-based gravity and EM geophysical measurements and software solutions for easier data interpretation using GisSOM, Advangeo® 3D Prediction, and 3D geophysical inversion software.

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Remote sensing methods and applied geophysics techniques gather information about subsurface structures without disturbance. Airborne surveys are preferred due to their speed, safety, and cost-effectiveness. Drone-based geophysical surveys are versatile, fast, economical, and ecologically friendly. However, drone payloads have limitations. Some geophysical methods are unsuitable for drones, and some may be prohibited by law. Drones have new opportunities in mining operations, especially for local scale support for ore and top cover volume estimations by repeated photogrammetry and lidar, constructions (roads, buildings), and a general understanding of geological bodies in large-scale pit mining, e.g. by hyperspectral imaging. Geophysical exploration requires larger drones for longer ranges. Magnetic measurements are the most mature technology, while electromagnetic sounding and gravimetry are still developing. The DroneSOM EIT project 2022-25 will develop these techniques.

Radai Ltd is developing a drone-based geophysical electromagnetic (EM) survey system called Louhi. It has two modes of operation – one uses a large loop on the ground as an EM source, while the other uses a small portable loop EM transmitter. Both systems utilize a lightweight 3-component EM receiver towed by a drone. The drone must be powerful, stable, and customizable to carry a payload of 2-3 kg in difficult weather conditions.

The first section describes Radai’s process of selecting the optimal drone platform for conducting EM surveys in the DroneSOM project.

The second section details the first flight tests conducted with the new drone platform and EM system.

Louhi is sensitive to variations in the electrical resistivity and magnetic permeability of the medium. As an airborne drone-based EM system, it avoids obstacles such as lakes, rivers, swaps, and ravines, making it safer and more cost-effective than ground EM surveys, especially in rugged terrain. Compared to manned aircraft, drone surveys are versatile, fast to deploy, economical, and ecologically friendly. However, the modest payload of drones imposes restrictions in the design and building of a drone-based EM system.

DTU Space is developing a gravity system based on an unmanned aerial vehicle (UAV) with a moving platform. The goal is to make the operation feasible by exploring new sensor systems. A new configuration called the strap-down configuration of an Inertial Measurement Unit (IMU) has many advantages over traditional gravity sensors. The IMU is physically fixed to the chassis of the aircraft, making it simpler, smaller, lighter, and requiring less power. DTU Space has been operating a strap-down IMU system routinely for gravity surveys since 2016. The current system, iCORUS1, weighs around 18 kg and consumes up to 175 W of power. Within the DroneSOM project, DTU Space is searching for alternative sensors.

The optimized gravimetry software’s status based on the first test campaigns for production flights at validation sites is reported. The software was developed using the DroneSOM test flight at Lindtorp Airfield, Denmark, and the first production flights in Sokli, Finland. The current software version was successfully used in processing an airborne campaign conducted by DTU Space on behalf of Kartverket. Further studies of GNSS tracking and interference will be conducted before the next field campaign. Finding an appropriate landing place for a fixed-wing drone is difficult, and a natural countermeasure is to localize alternative landing sites in advance.

Drones or Unoccupied Aerial Vehicles (UAVs) are used in geosciences to obtain data for investigating the topography, geography, and geology of an area. In the DroneSOM project, Radai Ltd is developing a drone-based geophysical electromagnetic (EM) survey system called Louhi. Louhi is based on EM induction and is sensitive to variations in the electrical conductivity of the subsurface materials. As an airborne drone-based EM system, Louhi avoids terrain obstacles and is safer and more cost-effective than ground EM surveys. This report describes the status of the semi-airborne version of the Louhi EM system and its towed receiver installation. It presents preliminary results from the airborne field test conducted in Lintumaansuo in Oulu, Finland, at the end of June 2023.