GEM Magnetometers

GEM’s Overhauser Magnetometer system is a revolutionary geophysical instrument developed by GEM to offer a rugged, low power, and sensitive alternative to Proton Precession and some other alkali vapour magnetometers.

GEM’s GSM-19 (Overhauser) magnetometer is a primary standard in mineral exploration and magnetic observatories. As a standard for magnetic observatories, this system has proven itself – for its high sensitivity, absolute accuracy and long life. Overhauser magnetometers are also used in archaeology, pipeline mapping, UXO detection, and other engineering and environmental applications.

GEM GSM-19: Cost Effective and High Presicion Magnetometer 


  • Sensitivity: 0.022 nT @ 1 Hz, (0.015 nT option)
  • Resolution: 0.01 nT
  • Absolute Accuracy: +/- 0.1 nT
  • Dynamic Range: 20,000 to 120,000 nT
  • Gradient Tolerance: Over 10,000 nT/m
  • Sampling Intervals: 60+, 5, 3, 2, 1, 0.5, 0.2 sec
  • Operating Temperature: -40°C to +50°C
Overhauser Magnetometers

a) Overhauser “Walking” Magnetometer/Gradiometer

A walking magnetometer/gradiometer is a high-sampling system capable of acquiring nearly continuous data. Key features are related to data quality, cost control and productivity as follows:

  • 0.022 nT @ 1 hz sensitivity for high sensitivity data acquisition
  • 5 samples per second acquisition for higher productivity (either by operator or on towed vehicles) and more data for decision-making
  • Ergonomic backpack and hands-free operation for greater operator ease-of-use and productivity

b) Overhauser “Mobile” Magnetometer/Gradiometer

A mobile magnetometer/gradiometer is a high sensitivity system capable of acquiring data at discrete stations. Key features are related to data quality, cost control and productivity as follows:
  • 0.022 pt/ÖHz sensitivity for high sensitivity data acquisition
  • Discrete data acquisition with sensor staff for routine application in various types of environments and terrains
  • All of the other features of “Walking” Overhauser magnetometers, including low weight for highly efficient operator functioning

c) Overhauser “Base” Magnetometer

A base magnetometer is a high sensitivity system capable of acquiring data at a regular interval throughout the day. Depending on the sampling requirements, it can be either a Fast sampling unit taking 5 samples per second (up to 5 Hz) or a Standard unit sampling at one sample every 3 seconds  (up to 0.33 Hz). Key features are related to data quality, cost control and productivity as follows:

  • The Overhauser base magnetometer has a high absolute accuracy. GEM is the global standard in Observatory magnetometers for this reason; the base magnetometer produces highly repeatable data as required in industry.
  • Three Base station programming modes are available for maximum productivity. These include daily (define working hours and minutes each day); flexible (up to 30 on/off periods) and immediate start.

Using either daily or flexible modes means that the operator is not required to return to the base station each day; data can be acquired with maximum efficiency and stored in high volume memory.

Benefits of Overhauser Magnetometers

Overhauser instruments come with excellent benefits for subsurface exploration. The Overhauser system offers an order-of-magnitude increase in sensitivity over GEM’s Proton system and matching sensitivities of some alkali devices. With data quality exceeding the standard proton precession, and comparable to the costlier optically pumped cesium magnetometer systems, the GSM-19 is a standard for many applications.

Overhauser magnetometers also provide high absolute accuracy, ruggedness, and reliability – as numerous systems are in operation around the world with an excellent performance record so that the GSM-19 can be counted on in any situation. Early versions of the Overhauser, developed in 1983, are still running on a continuous basis at an observatory in Japan.

GEM’s Overhauser Magnetometer with GPS sensor (top), console, and backpack. The system is extremely light and robust – making it an ideal choice for many subsurface investigations.

Overhauser offers the option of pulsed versus continuous operation. With pulsed operation, the system provides an energizing pulse to initiate the reading. With continuous operation, the system is always active – so that data can be recorded conveniently anywhere, at any time.

GEM’s Overhauser magnetometer/gradiometer also offers much less power consumption than Proton or alkali vapour systems so you can perform a whole day’s work on a single charge. Optional benefits include an omni-directional sensor (i.e. no dead zones) and fast sampling. Fast sampling of up to 5 Hz is available – an important capability for many larger surveys.  This fast sampling gives the option to automate readings on a vehicle such as an all-terrain-vehicle (ATV), snowmobile sled, etc.

The Overhauser Magnetometer does not require maintenance – it is as robust and effective an instrument as ever made for the field. It also has superior environmental specifications, which include an operating temperature of -40°C to +50°C; giving unparalleled performance throughout all survey conditions.

The cables and connectors have been carefully selected for maximum durability and performance. The light weight backpack gives hands-free operation while ensuring a stable, comfortable, and lightweight platform for making measurements.

Integrated GPS

Not only do our GPS technologies tell you where you have been, but they tell you where you need to go. This allows for highly accurate readings via ‘Waypoint Programming’ as well as accurate time synchronization for base station corrections.

With Waypoints, you design your survey on your personal computer and import the stations with ease into the magnetometer console. Then, the system will guide you to each Waypoint where a reading is to be made. With ‘Walking’ mode, you have a nearly continuous record of GPS-referenced data points – a major advantage in surveying because you save time in the field and it eliminates the possibility of positioning mistakes.

SENSYS Magdrone R3 - Drone/UAV Magnetometer Survey Kit

The MagDrone R3 is an ultra portable magnetometer survey kit to be attachable to any UAV / drone with a 1+kg payload only. The kit consists of Carbon fibre sensor tube with two built-in 3- axis Fluxgates, a 1-button data logger with internal SD card, rechargeable batteries, an integrated GPS as well as a serial live data output. It only needs some cable ties to mount the kit directly to the UAV. The MagDrone R3 is made and optimized for small and mid size survey UAVs that are shaped for less payload and longer flight times.

The MagDrone R3 survey kit can be used for general purpose surveys, science related magnetic cartographies, mine exploration, as well as for safety relevant operations such as area scanning for bombs and ammunition, preventive check and surveillance of areas and camps against intrusion. An associated software helps to identify flown tracks, cut, filter and compensate the raw data, generates a preview and exports into various formats to further process the recorded values i.e. using the MAGNETO® software, GIS tools or Matlab with your own scripting.


§ Autarkic system with two sensors, GPS, accelerometer and battery

§ Attachable to any UAV / drone with 1+ kg payload

§ 2GB nternal memory card

§ Power concept with function for data loss prevention

§ 200 Hz recording rate

§ 2 Hz live data output rate

§ USB download interface

§ Data processing tool



  • Survey & surveillance
  • Mine exploration / tracking / monitoring at flexible heights
  • Detection on unreachable, flooded or mined areas 


Technical Specifications:

Power Supply:  11.1 V; 1,950 mAh Li-Ion re-chargeable battery

Operating Temperature: -20°C to +50°C

Weight / with Li-Ion battery: 750 g / 884 g

Overall power consumption: 500 mA

Sensor tube dimensions: (W x D x H) 1,070 x 22 mm

FGM3D/75 Fluxgate

Number and orientation of sensors: 2 pieces, laid horizontal, parallel

Specified measurement range: ±75,000 nT (higher ranges available on request)

Number of sensor axis: 3

Distance between sensor centre points: 1,000 mm


Power: 50 mA

Sensor input: Internal wired

User Interface: On/Off + Start/Stop button; status LED

Survey mode: Recording when start/stop pressed

Sampling rate: 200 Hz (higher rates available on request)

Live data output: 2 Hz (via serial interface)

Internal memory: 2 GB

Datalogger dimensions: (W x D x H) 230 x 128 x 43/73 mm

Standard package

MagDrone R3: Sensor tube, 2 pcs. built-in FGM3D/75 sensors, data logger (fixed to tube), 2 pcs. rechargeable batteries

Rugged case: (W x D x H) 1120 x 290 x 110 mm

Internal GPS: U Blox PAM-7Q

Peripherals: Data transfer cables (USB), set of internat. power plugs, wall charger, accessory bags, USB memory stick with software

Documentation: Certificate, manual, quick guide

PC software: MagDrone DataTool

Optional accessories

Data processing: MAGNETO® Software

Live output: Serial Bluetooth dongle


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