Rugged Overhauser Magnetometer - GSM-19

Supplied By: GEM Systems, Canada

Introduction - Rugged Overhauser Magnetometer GSM-19

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.


The Overhauser system is a super-charged Proton magnetometer that uses a special mixture for energization and measurement. Overhauser offers a number of significant benefits over Proton and some alkali vapour systems.


The Rugged Overhauser Magnetometer, The GSM-19 v7.0, is the total field magnetometer/gradiometer of choice in today's Earth Science environment - representing a unique blend of physics, data quality, operational efficiency, system design and options that clearly differentiate it from other quantam magnetometers


With data quality exceeding standard proton precession and comparable to costlier optically pumped cesium units, the GSM-19 is a standard in many applications, including:

    • Mineral Exploration (airborne and ground base station)

    • Environmental and Engineering

    • Pipeline Mapping

    • Unexploded Ordinance Detection

    • Archaeology

    • Magnetic Observatory Measurements

    • Volcanology and Earthquake Prediction

Proton Magnetometers and GradiometersProton Magnetometers and Gradiometers


Overhauser Magnetometer System Types

Overhauser "Walking" Magnetometer/Gradiometer System: Primarily used for high sensitivity, nearly continuous surveys

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 pt/ÖHz 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

Overhauser “Mobile” Magnetometer/Gradiometer System: Primarily used for high sensitivity, discrete surveys

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

Overhauser “Base” Magnetometer System: Primarily used for repeatable, accurate base station readings

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 “Walking”/Fast sampling unit (up to 5 Hz) or a Standard sampling unit (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



    • Sensitivity: 0.022nT @ 1Hz

    • Resolution: 0.01nT

    • Absolute Accuracy: ± 0.1 nT

    • Range: 20,000 to 120,000 nT

    • Gradient Tolerance: > 10,000 nT/m

    • Samples at: 60+, 5, 3, 2, 1, 0.5, 0.2 sec

    • Operating Temperature: -40°C to 55°C

Operating Modes

    • Manual: Coordinates, Time, Date and Reading stored automatically at min. 3 sec. interval

    • Base Station: Time, Date and Reading stored automatically at 1 to 60 sec. intervals

    • Remote Control (Optional): RS-232 interface

    • Input/Output: RS-232 or analog (optional) output using 6-pin weatherproof connector with USB adapter

Storage (# of Readings)

    • Mobile: 1,465,623

    • Base Station: 5,373,951

    • Gradiometer: 1,240,142

    • Walking Mag: 2,686,975


    • Console: 223x69x240mm

    • Sensor: 175x75mm diameter cylinder


    • Console with Belt: 2.1kg

    • Sensor and Staff Assembly: 1.0kg

Standard Components

    • GSM-19 Console

    • GEMLink Software

    • Batteries

    • Harness

    • Charger

    • Sensor with Cable

    • RS-232 Cable and USB adapter

    • Staff

    • Instruction Manual and Shipping Case

Optional VLF-EM

    • Frequency Range: Up to 3 stations between 15 to 30kHz

    • Parameters: Vertical in-phase and out of phase components as % of total field

    • 2 components of horizontal field amplitude and total field strength in pT

    • Resolution: 0.1% of total field

Overhauser Benefits

The GSM-19 is designed to be a mid-range instrument with excellent benefits for subsurface exploration. As a mid-range instrument, 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.


But the benefits do not end there. 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.


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. Other 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 that may be of interest. These fast sampling gives the option to automate readings on a vehicle such as an all-terrain-vehicle (ATV), snowmobile sled, etc.


The Overhauser effect occurs when a special liquid (with unpaired electrons) is combined with hydrogen atoms and then exposed to secondary polarization from a radio frequency (RF) magnetic field


The unpaired electrons transfer their stronger polarization to hydrogen atoms, thereby generating a strong precission signal that is ideal for very high sensitivity total field measurements.


In comparison with proton precession methods, RF signal generation also keeps power consumption to an absolute minimum and eliminates noise (i.e. generating RF frequencies are out of the bandwidth of the precession signal).


In addition, polarization and signal measurement can occur simultaneously - which enables faster, sequential measurements. This, in turn, facilitates advanced statistical averaging over the sampling period and/or increased cycling rates (i.e. sampling speeds)


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 GSM-19 is perhaps the world’s most prosperous magnetic instrument, based on its ongoing development that continues to this day. In fact, the system is almost unbreakable as our clients continue to prove in their daily work. The mechanics of the magnetic sensor and console have been ruggedized from previous versions while maintaining environmental specifications and weatherproof characteristics.


Moreover, the cables and connectors have been carefully selected for maximum stability and performance. An improved backpack gives hands-free operation while ensuring a stable, comfortable, and lightweight platform for making measurements. All considered, this is an excellent product from an experienced instrumentation provider.


Value Adding Features

    • Data export in standard XYZ format for easy use in standard commercial software programs

    • Programmable export format for full control over output

    • GPS elevation values provide input for geophysical modeling, Enhanced GPS positioning resolution

    • Standard GPS Option B:0.7 SBAS (WAAS, EGNOS, MSAS)

    • High Resolution GPS Option D

        • 0.6m SBAS (WAAS, EGNOS, MSAS)

        • 0.6 OmniStar(VBS2 subscription)

    • Multi-sensor capability and VLF-EM option for advanced surveys

    • Picket and line marking/annotation for capturing related survying information on the go


Key System Components

Key components that differentiate the GSM-19 from other systems on the market include the sensor and data acquisition console.


Sensor Technology

GEM;s sensors represent a proprietary innovation that combines advances in electronics design and quantum magnetometer chemistry


ELectronically, the detention assembly includes dual pick-up coils connected in series opposition to suppress far-source electrical interference, such as atmospheric noise. Chemically, the sensor head houses a proprietary hydrogen-rich liquid solvent with free electrons (free radicals) added to increase the signal intensity under RF polarization.


All sensor components are designed from carefully screened non-magnetic materials to assist in maximization of signal to noise. Heading errors are also minimized by ensuring that there are no magnetic inclusions or other defects that could result in variable readings for different orientations of the sensor


Optional omni-directional sensors are available for operating in regions where the magnetic field is near-horizontal (i.e. equatorial regions). These sensors maximize signal strength regardless of field direction


Data Acquisition/Console Technology


Console technology comprises of an external keyboard, display interface with internal firmware for frequency counting, system control and data storage/retrieval. For operating convenience, the display provides both monochrome text as well as real-time profile data with an easy to use interactive menu for performing all survey functions.


The firmware provides the convenience of upgrades over the internet via the GEMLink software. The benefit is that instrumentation can be enhanced with the latest technology without returning the system to GEM resulting in both timely implementation of updates and reduced shipping/servicing costs.


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