GSM-19 Overhauser Magnetometer/Gradiometer System
Version 5

New Case Study

GSM-19 Overhauser Magnetometer
Gsm-19 overhauser magnetometer
New! version 6

Features of the magnetometer
  • Sensitivity = 0.02 nT
  • Absolute Accuracy = 0.2 nT
  • Sample Rates up to 5 Hz
  • Low Power Consumption
General magnetometer description
"Overhauser" Once you experience it, you'll never go back to proton. Overhauser technology brings you sensitivities one to two orders of magnitude better than proton, yet in a light weight package. This is because the overhauser magnetometer consumes an order of magnitude less power than proton magnetometer, allowing a lighter weight for batteries.

What is the Overhauser technique? The Overhauser sensor contains the electrons' fluid that has been added to a hydrogen rich in the form of "free radial". The resulting mixture yields a sensor with 5000 times gain in proton polarization. Since the Overhauser polarization effect does not require static magnetic fields, but uses radio frequency fields transparent to protons, measurement can be done concurrently with polarization. The result is a sensor with much greater sensitivity, that can be sampled much more rapidly than the standard proton sensor.

Overhauser magnetometer systems therefore maximize resolution while minimizing power consumption. Even with Walking Gradiometer systems, sampling at rates of once per second or betterare posible; Even in cold temperatures of minus 40 zero degrees Celsius and greater, the internal rechargeable battery can still be relied on for a 10 hour day, or longer.

The GSM-19 Overhauser magnetometer is thus truly a State-of-the-Art Magnetometer / VLF system. The GSM-19 offers the data quality, reliability, and extensive list of capabilities, and options, that allow it to meet a very wide spectrum of applications.

Standard Features of the Magnetometer

The GSM-19 magnetometer console features a real time graphic display of the current profile. In addition digital display of the current reading, current position, and warning messages are provided. The console design, with internal rechargeable battery pack, allows the unit to be completely sealed against the elements. With the built in heater for the display the GSM-19 magnetometer is ready to go wherever your surveys may take you.

Tuning is automatic worldwide, with provision for manual override. In high gradient conditions the GSM-19 magnetometer monitors the signal decay rate and displays a warning message when the gradient becomes too great. Filters for rejection of 50 or 60 Hz noise are provided.

Diurnal corrections may be done in traditional fashion with one magnetometer unit as a base station and a second unit used as the mobile field unit. At the end of the survey the two units are connected and the field unit creates a corrected data file (which still includes the raw data file) based on the temporal drift recorded by the base station.

As a standard feature GSM-19 magnetometer also offer the capability of making tie point measurements for automatic diurnal corrections. To use this feature the operator records a base value and then loops back to this point periodically during the survey to record another measurement, and thus build a file of the drift. In this way a single instrument may be used to make diurnal corrections.

The RS-232 port on the GSM-19 magnetometer will output data as it is collected. This allows interface to GPS loggers that will accept RS232 data. The standard GSM-19 magnetometer may be operated in a remote mode via computer. Memory storage is 512 K in the standard unit, and may be upgraded to 2 MB.

Grid coordinates are stored with either numeric or compass designations. A seven digit number may be used to designate lines and positions. Line and position spacing is entered so that with every reading the position may be automatically updated. An End of Line feature allows the next line to be quickly selected, plus changes the sign on the position spacing. If the previous line had been adding positions as the operator moved, then on the next line, positions will be subtracted as the operator moves. The operator may also easily manually enter his grid position for cases where gaps in the line are necessary.

Equatorial Sensor for magnetometer
In equatorial regions, generally 30 degrees north or south of the equator, magnetic fields reach a nearly horizontal angle with the earth's surface. This requires a conventional proton sensor to be used in an inverted position, and requires the operator to collect data only on east/west lines to maximize the magnetic signal. This is a problem that is a magnitude worse for cesium magnetometers.

The Overhauser technique allows design of an optional sensor completely free of this problem, a sensor that requires no orientation no matter what the latitude of your exploration. This can be a major advantage when working in diverse areas around the world, and when needing to train local operators whose first language may not be your own.

"Walking Mag Option"
The GSM-19 magnetometer is the first to offer the "Walking Mag" concept. The reason for this is the outstanding advantage the Overhauser sensor has in this application. With the "Walking Mag" option the operator may select a sample rate of up to two samples per second. At this rate Overhauser technology can still deliver a noise level that is quite acceptable, about 0.1 nT, and the lower power consumption means that a full day of surveying can still be done with just the internal rechargeable battery.

As shown in Figure 1 the near continuous data from the "Walking Mag" technique provides increased definition for any type of survey. For surveys with densely spaced grids, such as archaeological or environmental surveys, field productivity is markedly improved, typically by a factor of five.

When in the Walking Mag mode the operator still presets his line and station spacing. When a known station is passed a grid update key is pressed and the current reading is tagged with this station. Readings taken between these marked positions are then linearly interpolated for their grid position when data is transferred to a computer.

A further refinement of the Walking Mag concept is the Hip Chain Option. This option uses a hip chain to trigger the magnetometer to take a reading at discrete intervals. A Hip Chain consists of an optical encoder that records revolutions of a wheel wound with disposable cotton string. The string is tied off at the beginning of a line, and as the operator walks the string is pulled out, and the magnetometer is automatically triggered. With the Hip Chain option sample rates up to five samples per second are supported.

Omnidirectional VLF
The GSM-19 VLF features a three coil design, with new larger coils in 1997, to achieve a non orientation capability with excellent sensitivity. Up to three VLF stations may be recorded, along with the magnetic reading, with the pressing of a single key.

As each VLF station is read the total field strength is displayed. This value may be used to determine if a station's signal is strong enough to obtain useful data. At the end of each reading the in phase, out of phase, and horizontal components are displayed and recorded for each station.

To determine what stations are available the Scan feature may be used. The entire VLF spectrum is scanned and stations with their corresponding signal strength are displayed. Automatic tilt compensation is provided up to ten degrees. Beyond this a warning message appears with display of the amount of tilt in each direction, enabling the operator to correct his position and take the reading again.

For Walking Mag applications a Walking VLF option is also available. With this option a single VLF station may be measured at sampling rates up to once per second. In this mode both magnetic and VLF readings may be collected at the one hertz rate.

Simultaneous Gradiometer
Many mining, environmental, and archaeological applications may benefit from using the gradient measurement. For near surface anomalies, generally twenty meters depth or less, the gradient anomaly will be larger, and narrower, than the total field anomaly. This permits the more accurate location of the target, and gives better sensitivity. The gradient measurement has the added value of being free from diurnal drift.

The most accurate gradient measurements are made when both sensors are polarized and measured at precisely the same time. In this way any slight movement of the sensor staff pole will not affect the reading. With the GSM-19 Gradiometer Option the pressing of a single key will initiate measurement of both the total field and gradient. Both readings are displayed and stored.

Integrated DGPS
With the GPS Log Option the GSM-19 magnetometer will display and store GPS data using standard NMEA format. Position accuracy is dependant on the user's DGPS system.

Also offered is an internally mounted GPS board that may be integrated with radio modem for DGPS mode. A range of GPS boards may be offered to meet customer specified accuracy. These are quoted on a case by case basis to take advantage of current technology. Complete systems, with base station, and DGPS software are provided.

Extended Remote Control
As an option the GSM-19 magnetometer may be completely controlled through the RS232 interface. This option includes all controls available from the keypad, such as power on/off, tuning. etc. This option is most useful for observatory applications.

Marine Magnetometer
The Overhauser effect is a major benefit in marine applications. The GSM-19 has been developed into two marine models; the GSM-19M for shallow tow applications with cable lengths of up to 100 meters; and the standard GSM-19 for tow applications with cable lengths of 30 meters.

A standard GSM-19 magnetometer may be used with a marine sensor with up to a 30 meter cable. In this way the same console may be used for both land and marine applications. Users considering this option may want to focus on also including the Walking Mag option so that they will have sample rates that are more appropriate for marine applications.

Specifications

Overhauser Performance

Resolution: 0.01 nT
Relative Sensitivity: 0.02 nT
Absolute Accuracy: 0.2nT
Range: 20,000 to 120,000 nT
Gradient Tolerance: Over 10,000nT/m
Operating Temperature: -40°C to +60°C
Operation Modes
Manual: Coordinates, time, date and reading stored automatically at min. 3 second interval.
Base Station: Time, date and reading stored at 3 to 60 second intervals.
Walking Mag: Time, date and reading stored at coordinates of fiducial.
Remote Control: Optional remote control using RS-232 interface.
Input/Output: RS-232 or analog (optional) output using 6-pin weatherproof connector.
Operating Parameters
Power Consumption: Only 2Ws per reading. Operates continuously for 45 hours on standby.
Power Source: 12V 2.6Ah sealed lead acid battery standard, other batteries available
Operating Temperature: -50°C to +60°C
Storage Capacity
Manual Operation: 29,000 readings standard, with up to 116,000 optional. With 3 VLF stations: 12,000 standard and up to 48,000 optional.
Base Station: 105,000 readings standard, with up to 419,000 optional (88 hours or 14 days uninterrupted operation with 3 sec. intervals)
Gradiometer: 25,000 readings standard, with up to 100,000 optional. With 3 VLF stations: 12,000, with up to 45,000 optional.
Omnidirectional VLF
Performance Parameters: Resolution 0.5% and range to ±200% of total field. Frequency 15 to 30 kHz.
Measured Parameters: Vertical in-phase & out-of-phase, 2 horizontal components, total field coordinates, date, and time.
Features: Up to 3 stations measured automatically, in-field data review, displays station field strength continuously, and tilt correction for up to ±10° tilts.
Dimensions and Weights: 93 x 143 x 150mm and weighs only 1.0kg.
Dimensions and Weights
Dimensions:
Console: 223 x 69 x 240mm
Sensor: 170 x 71mm diameter cylinder
Weight:
Console: 2.1kg
Sensor and Staff Assembly: 2.0kg
Standard Components

GSM-19 magnetometer console, harness, battery charger, shipping case, sensor with cable, staff, instruction manual, data transfer cable and software.

Ordering Information
Description
  Order Number
GSM-19 overhauser magnetometer 350-170-0051
Gradiometer Option 350-170-0042
VLF Option 350-170-0069
GPS Log Option 350-170-0170
Memory Upgrade per 512 350-170-0065
Analog Output 350-170-0040
Remote Option 350-170-0043
Walking Mag Option 350-170-0072
GSM-19 Shallow Marine Fish 350-170-0105
Equatorial Sensor Option 350-170-0114