A magnetic field is the area around a magnet, magnetic object, or an electric charge in which magnetic force is exerted. Earth behaves like a giant magnet.
The two primary characteristics of magnetic fields are their strength (referred to as magnetic flux density or magnetic induction) and direction.
A magnetometer is a device that measures the magnetic field at a point where it is.
Types of Magnetometers
Fig.1 - Schematic illustration showing Earth’s magnetic field
Fun fact
Magnetic compasses, which have existed for thousands of years, also can be treated as “mechanical magnetometers,” which measure the direction of magnetic field only.
Besides scientific purposes, magnetometers are used to detect objects that create anomalies in the Earth’s magnetic field. These objects typically contain ferrous (iron-containing) materials. When they are surrounded by external magnetic fields (the magnetic field of the Earth first of all), they interact with it and create “anomalies” or changes of magnetic field properties (strength and direction) around the object. On the other hand, “non-magnetic” materials will not do that.
Examples of detectable objects: iron ore deposits, buried utilities, unexploded ordnance (UXO), archaeological artifacts, submarines, and other ferrous metal items.
Underground Pipe
Landmine in a Metal Case
Steel Barrel
Iron Ore
Examples of non-detectable objects: Materials like gold nuggets (yes, it is NOT possible to detect gold nuggets using magnetometers), plastic-cased landmines, plastic barrels, and copper wires, as they do not significantly alter the magnetic field.
Gold Nugget
Landmine in a Plastic Case
Plastic Can
Copper Wire
By measuring the magnetic field at multiple points across a search area and analyzing the data, magnetometers can identify anomalies where the magnetic field differs from the average level. These anomalies often indicate the presence of magnetic objects hidden beneath the surface.
The most common measurement unit for the magnetic flux density (or magnetic induction) is nanotesla (nT). It’s what you will get in the results of measurements, magnetometer data files, etc.
Typical survey grid planned with UgCS
Fig.2 - Magnetic Survey Grid Planned in Drone Flight Planning Software UgCS over SPH Engineering’s geophysical sensor Test Range
The result of the magnetic survey with Oasis montaj
Fig.3 - Magnetic map and plot of magnetic field strength along one survey line (data is courtesy of SENSYS GmbH.). The anomaly corresponds to the German WW2 Flam C-250 aerial bomb (without tail) lying 1.5m deep under the surface.
SPH Engineering has a portfolio covering all possible applications of airborne (drone-mounted) magnetometers. More importantly, our magnetic survey solutions have been rigorously tested in diverse environments such as Greenland, Iceland, Papua New Guinea, Israel, Chile, the US, and many European countries, including real UXO searches. We have a collection of best-in-class magnetometers and understand their benefits for particular applications.
SPH Engineering MagNIMBUS | SENSYS MagDrone R1 | SENSYS MagDrone R3 | SENSYS MagDrone R4 | Geometrics MagArrow | |
|---|---|---|---|---|---|
| Sensor | 1x or 2x QuSpin QTFM G2 laser-pumped rubidium total field sensors | 1x FGM3D/75 fluxgate triaxial sensor | 2x FGM3D/75 fluxgate triaxial sensors | 5x FGM3D/75 fluxgate triaxial sensors | 2x MFAM laser-pumped cesium |
| Sensor sensitivity | Very high | High | High | High | Very high |
| Geology & mineral exploration |  | | |||
| Environmental (abandoned wells, pipes, storage tanks, etc.) | | | | | |
| UXO (unexploded ordnance) search | | | | | |
| Locating buried infrastructure (metal pipes, shielded cables, and cables under load) | | | | | |
| Tramp metal and lost GET (ground engagement tools), pieces of metal detection | | | | | |
| Archaeology | | | | | |
| Notes for applications | • Foldable arm for sensor allows extremely low sensor-ground clearance for UXO search and similar tasks. • Gradiometer configuration simplified data processing and makes possible surveys in presence of external sources of EM fields (power lines etc.) • Very light and compact, ideal for confined and small areas. • Good wind resistance. | • Foldable arm for sensor allows extremely low sensor-ground clearance for UXO search and similar tasks. • Very light and compact, ideal for confined and small areas. • Good wind resistance. | • Light and compact, ideal for confined and small areas. • Good wind resistance. | • Spatial resolution of data is 2 times better than R3. • Wider coverage for single survey lines. | • Mounted on suspension cords. • Not convenient for low altitude and rough terrain (mountains etc.). • Bad wind resistance, especially for side wind gusts. • Optimal for the long smooth survey lines when the drone may fly at full speed with minimum changes in speed or direction. |
| Distance between survey lines | 0.5-1 m | 0.5 - 1 m | 2 m | 2.5 m | - |
| Flight altitude* | 1.5 m AGL | 1.5 m AGL | 1 m AGL | 1 m AGL | - |
| Speed (should be selected according to relief and vegetation) | up to 10 m/s | up to 10 m/s | up to 8 m/s | up to 6 m/s | - |
| Live data stream to the ground station | | | |||
| Sampling rate | User configurable: • up to 500 Hz in scalar mode • Good wind resistance. | 250 Hz | 250 Hz | 200 Hz | 1000 Hz |
| Weight | • 0.7 kg (1 sensor) • 1.2 kg (gradiometer) | 0.7 kg | 1 kg | 2.7 kg | 1 kg |
| Recommended drone* | Larger drones like • DJI M600 Pro • IF1200A • or similar | ||||
| Export restrictions | No • (end-use certificate required) | No | No | No | Yes • (ITAR free version available upon request) |
Remarks
• For MagNIMBUS and MagDrone R1 flight altitude of 1.5 m AG means sensor-ground clearance of 0.5 m, providing extreme detection capabilities for small ferrous items.
• Flight parameters for surveys like mineral exploration vary in very wide extents. Altitude can be up to 50m (above possible obstacles and trees), distance between survey lines usually the same as the altitude. Flight speed can be the maximum safe/economical speed of the drone.
• We recommend larger drones for MagArrow because it uses 4x 3m long suspension cords, and for better sensor stability separation between attachment points should be at least 1m. MagArrow can be used with smaller drones like DJI M350 RTK, but its stability will degrade.
Regardless of the application scenario, magnetometers measure the same, but different survey objectives dictate requirements for flight patterns (altitude, survey lines separation) and the optimal type of magnetometer.
| Survey objective | Sensor-ground clearance | Survey lines separation | Speed | Recommended magnetometer type |
|---|---|---|---|---|
| UXO detection and similar environmental applications, including archaeological site surveys | 0.2 to 5 m, typically <1 m | 1 m | Maximum safe speed according to the terrain | MagNIMBUS MagDRONE R4/R3/R1 |
| Geological mapping in general at prospect scale or for detailed mineral exploration with the capability of detecting weakly magnetic targets (e.g., mineral sands strand lines) or distinguishing deeper targets beneath shallow sources of geological noise (e.g., maghemite, rich regolith, laterites, or shallow surficial volcanics) | 5 to 30 m | the same as sensor/ground clearance | Maximum economical speed of the drone with payload | MagNIMBUS MagArrow |
| Abandoned cased wells, pipelines, buried services, and waste dump site detection | >5 m | the same as sensor/ground clearance | Maximum economical speed of the drone with payload | Any available magnetometer system |
Useful Resources
Resources providing an introduction to the basics of aerial magnetic surveys, covering detection ranges and practical low-altitude uses. It’s an excellent guide for a deep and informative overview.
And we will tell you how to implement a magnetic survey technology for your application
There are several standard methods for conducting magnetometer surveys, each with its own benefits and drawbacks. No single method is universally applicable; the appropriate or most suitable approach should be chosen based on the survey target and environmental conditions.
+ Very high productivity: hundreds (for helicopters) or even thousands (for airplanes) line kilometers per day
+ Maybe cost-effective in case of large, hard-to-reach areas
- Very expensive
- Requires extremely skilled pilots and personnel
- Applicable for mineral exploration and geological surveys only and for specific tasks like submarine hunting. Search for the small targets (UXO, etc.) is not possible
- Can be dangerous, especially in mountain areas
+ Not qualified personnel can be used for data collection after short training
+ Maybe the only option to collect hi-resolution data in forested areas where it is not possible to use airborne methods (drones)
- Very low productivity
- Hard to use in areas where the surface of the ground is not suitable or safe for walking
- Additional QA (quality assurance) measures may be necessary in case of use of not qualified personnel for data collection
+ High productivity
+ Good to high data quality
- Applicable only for relatively flat areas without obstacles and vegetation and surfaces with enough bearing capacity
- High cost of the survey system (proportional to the number of sensors in the array)
+ High productivity
+ Good to high data quality
+ Data quality is predictable, with minimum influence of human errors or behavior (precision of following of survey lines, etc.)
+ Low to average cost of surveys in terms of price per km
+ The only approach with zero risk for field personnel
- Maybe not cost-effective for very large areas
- Requires qualified personnel for data collection (drone operators)
Drone-mounted magnetometer systems include not only drone and magnetometer payload. SPH Engineering supplies end-to-end solutions for every particular application.
Compatible drones: DJI M300/M350/M600, Inspired Flight IF1200A or IF800, Harris Aerial H6, and Wispr Ranger Pro and similar UAV
And we will help you choose the best option
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