By Dipl.-Ing. Wolfgang Süß, Managing Director, SENSYS
The scope of this article is to illustrate the current state of airborne magnetics as a commercial and viable solution already in use worldwide for commercial, defense, but humanitarian applications. The last decade of technology evolution brought a massive innovation in the area of remotely operated platforms on land, water and in the air. Self-established vehicles with open-source software were replaced by commercial off the shelf solutions integrating a vast number of sensors for operation, navigating and obstacle avoidance in the field.
Unmanned aerial vehicles (UAVs), Unmanned ground vehicles (UGVs) and Unmanned surface vehicles (USVs) are already in daily operation for manifold tasks like surveillance of properties, industrial inspection and monitoring of machineries or industrial chimneys, agricultural support, parcel services, orthophotography and 3D modelling of mining areas or building yards.
Sensitive fields like the search for and detection of bombs, ammunition, mines and IEDs are still underdeveloped or at least the commercial solutions are underrated. A number of grants and scientific studies already led to very different solutions using large drones to carry ground-based designed equipment to showcase a new approach to the hazardous groundwork of people within mine fields. At the end, the challenges of financing a truly technology-driven solution, turning labor costs and competencies upside down as well as having different technical solutions for single use cases, made remote operated sensor platforms less attractive. Nevertheless, the market offers a few technology packages combining a commercial drone with additional computing power and magnetometers for simple, but professional use in the field of UXO detection, area observation and project quality control.
SENSYS is a manufacturer of magnetometer and Time Domain Electromagnetics (TDEM) solutions for monitoring, detection and analysis of areas and objects. The company was founded in1990 and is based in Germany, East of the capital Berlin. Since then, the company grew to 50 employees developing, producing and servicing single Fluxgate Magnetometers, hand-held devices, multi-sensor systems to be operated by man, car or remote platforms on land, underwater or in the air. Commercial companies, the defense industry, military and NGOs are using the equipment in more than 90 countries worldwide. SENSYS products are designed for simple operation in harsh field conditions, providing excellent data.
Clients like AIRBUS, Rheinmetall, SafeLane Global and many others rely on SENSYS solutions within their projects.
The company focus on Fluxgate Magnetometers allows SENSYS to optimize the sensor technology and enable customization for different applications. Magnetometers are passive sensors that are recording magnetic intensity. Comparable to the principle of a temperature sensor, Fluxgates measure at the point of the sensor itself (not at any distance, nor having a certain angle of operation). That way a Fluxgate sensor
is always measuring the Earth’s Magnetic field. Ferrous objects are distorting the Earth magnetic flux lines in their proximity. Thus, when a sensor comes close to a buried object, it detects the anomaly in the Earth’s magnetic field. Assuming an ambient Earth’s magnetic field of around 60,000nT, the sensor noise of SENSYS produced Fluxgate Magnetometers is as low as 0,006nT; therefore, SENSYS sensors can detect changes in the magnetic flux as low as the 10 millionth part of the Earth’s magnetic field.
The illustration opposite shows how fast a magnetic field of an object (physically described via its magnetic moment in Am2) decreases over distance. That means, that the best chance for detecting of buried objects, is always by getting as close as possible to or even into the ground (e.g. borehole / drilling surveys).
The journey towards airborne solutions started in 2015, when SENSYS investigated into drone-based Magnetometer surveys. Using a self-assembled octocopter with an open-source control software, first flights were bumpy and to be safe we maintained a distance to ground of several meters. The approach of hanging the very sensitive Fluxgate Magnetometers away from the drone was good, but not practical at all as that resulted in unstable flight controls of the drone. The sensors were swinging heavily during flight, so that a precise positioning of the sensor data on the color code magnetic map was impossible. Also, at this time, standardized interfaces to the drone (GPS, control, power) were not available, so that the drone integration was a hassle.
With two years of research, trials and prototyping, SENSYS focused on a compact 2-sensor solution with its own battery, GPS and data storage, called MagDrone R3. With only 800g weight and no efforts to integrate and fly the device it rapidly made its way into Geophysics, Mining and Exploration. Everybody who had to operate a Cessna, two pilots and heavy equipment on board could now cover the same work (and produce better data) with a backpack loaded with a small commercial drone and the SENSYS MagDrone R3 survey kit.
With a growing market asking for more efficient solutions, SENSYS released the 5-sensor MagDrone R4 in 2020 offering a 2.5m span/swath to be mounted on most commercial UAVs with 2kg payload. The system has 5 sensors, separated 50cm from each other. The installed Fluxgates are triaxial Magnetometers, whereas all axes (x, y and z) from each sensor are recorded separately 200 times per second, generating 18,000 measurement values per minute. The 200 Hz sampling rates allow for fast flights without losing data density. At the same time, the low weight of the MagDrone R4 supports the use of small drones and stable flight conditions.
At the same time, DJI released its flagship model M300 and the Latvian company SPH Engineering reached a point in product stability with their UgCS Skyhub TTF (true terrain following). Using the M300 as the main platform and adding the SkyHub for overruling DJI’s flight control, enables us to conduct close ground flights with terrain following mode. Furthermore, the SkyHub controller can export the DJI GPS information and forward to the SENSYS MagDrone R4 for a direct RTK GPS based georeferencing of all measurement data. With controllable interferences of mounting the MagDrone R4 directly into the landing gear, the setup of the UAV magnetometer survey system is as compact as possible, as well as it ensures an excellent maneuverability of the UAV. A powerful MagDrone DataTool can process and filter the data to cancel detected rotor noise off the survey data, concentrating on buried structures and objects in the ground.
The use of the MagDrone in dozens of customer projects shows that this product is way beyond being developed, it has long become an ex-stock off-the- shelf solution for our markets.
To further approve the combination of DJI M300, SkyHub controller and MagDrone R4 magnetometer kit for the detection of ferromagnetic mines, the Croatian Mine Action Centre – Centre for Testing, Development and Training (HCR-CTRO) conducted a field survey on their Benkovac test site, which has 90 ferromagnetic mines buried at different depths up to 25cm 1 . The results were presented at the 19th International Symposium – Mine Action 2023, in Vodice, Croatia on May 4th to provide awareness of the capabilities of such a detection system.
Another campaign was executed by the Heinz Sielmann Foundation and the German Institute for Federal Real Estate (BImA) on the ground of the foreign military training range Kyritz-Ruppiner Heide with the so-called Bombodrom as central drop zone, North of Berlin. Since the Kyritz-Ruppiner Heide has been intensively used for military purposes by the Soviet armed forces since 1950 and later by the German Federal Armed Forces, up to 1.5 million tons of explosive ordnance are suspected around the former Bombodrom.
Nowadays, the Heinz Sielmann Foundation is responsible for the maintenance of the heath, it is important to define contaminated areas and to make it easier to plan both the risk and the use of technology on these contaminated areas.
A range of different ammunition was surveyed to formulize the capabilities and limits of the airborne survey system, which will help to better plan pre-scans of areas for risk mitigation as well as the implementation of quality control checks before and after field work. The results are promising as long as the field conditions allowed for shallow flight in the range of 0.5 to 1m above the ground. Since a lot of ammunition is of less ferrous material, the magnetic signature of these UXO items is weak. For example, some small cases of 20mm, 23mm and 30mm diameter were hard to detect, whereas all the grenades of 57mm diameter, TM62 tank mines, pieces of mortar shells and steel wires were clearly detected. Hence, the survey system needs to operate close to and be stable above the ground at constant conditions (also within the drone) to be able to distinguish magnetic noise from UAV movements, electronics and rotors.
As explained initially, Magnetometers do not have an opening angle, but operate at the point of their sensor head. Because of that, a scan of the entire area is required. The usual distance between two sensor tracks is 25 or 50cm. As the MagDrone R4 has a sensor frame with sensors at 50cm spacing each, the UAV detection system needs to fly a line every 2.5m. With 30-40 minutes flight time with hot-swappable batteries the daily coverage can be up to 30 hectares. Such, that was done during a historical study by the Bavarian State Department of Monuments and Sites at Ganacker, Bavaria 2 . This site is a former “Luftwaffe” operational airfield. Since February 1945 and under inhumane conditions, forced laborers were used to build a runway for the Messerschmitt Me-262 jet-powered fighter aircraft. Towards the end of the war, the airfield was attacked several times by Allied air forces (low-level attacks and bombardments). Within 4 days 120ha of data were generated, flying 8 hours each day. The tracks were up to 700 meters long, where the DJI M300 was flying with 5 meter per second at 1 meter above ground level. Downtimes to change batteries were around 30 seconds each.
Especially for historical and infrastructural surveys, the dense coverage of an entire area allows to reveal the bigger picture of activities, buried infrastructure and link between single anomalies in the ground.
The benefits of using aerial approaches are obvious. With no contact to the ground, the safety of involved operators and EOD technicians is increased as nobody needs to enter the area of interest. Radio connection between UAV and operator’s controller is several kilometers, which allows to also survey large areas from outside. Another advantage is the precise GPS and a click-and-tick pre-flight planning of the survey area and flight lines of the drone. The operator is not steering the UAV anymore, but only acting as a supervisor and backup in case of failure. During normal operation, the UAV can fly very straight and precise tracks, having an onboard obstacle detection and (preferably) the true terrain following mode contributing to increase efficiency of data generation and field coverage. Last, but not least is the advantage of redundancy. On one side, the failure of a single sensor in a multi sensor’s systems is much better detected and compensated by the other sensors. With pre-planned automated flights and data collection, a survey can be repeated anytime. That allows a comparison before and after, which opens the door for more efficient quality control mechanisms within sensitive projects such as UXO and mine – clearance.
In summary, the industry reached a point in technology were the use of UAVs within sensitive projects on hazardous areas is viable in terms of achievements compared to the money to invest, as all used products are commercially available. The presented airborne magnetometer system using the DJI M300, the SkyHub controller and the MagDrone R4 is already in use on a number of former military sites such as in Germany or the Ukraine. With a pre-planning of the survey area, the UAV will work its way autonomously through the field at minimum heights of 0.5 to 1 meter, 5 meter per second flight speed, entirely covering up to 30 hectares within a single day. In the context of EOD, such a system is detecting shallow small ferrous items up to deeply buried large bombs. This provides a great chance to integrate a UAV based magnetometer system into large area investigations or follow on quality controls.
A challenge surely remains with non-ferrous objects, such as mines or IEDs as well as surveying on highly mineralized soils. This is due to the nature of magnetics. At SENSYS, this challenge is under investigation opting for electromagnetic sensors to be integrated or even combined with the Fluxgate sensors to maximize the detection capabilities.
- Milan Bajić, Markus Schikorra “Detection of ferromagnetic landmines with a UAV-based magnetometer, demonstration, and verification”, Mine Action Symposium 2023
- Andreas Stele 1, Roland Linck, Markus Schikorra “Large- scale UAV magnetometry on a former World War II airfield at Ganacker (Lower Bavaria, Germany)”, DGG 2022
ABOUT THE AUTHOR
Since 2016, Wolfgang Suess is one of the Managing Directors at SENSYS and responsible for Sales, Marketing and Strategic Growth. Before, he worked for global companies like AIRBUS Industries and BOMBARIDER Transportation in several roles in Engineering, Product Design and Innovation, after he finished his study of Information Technologies in 2004.
Counter-IED Report Spring/Summer 2023