GSM-19 Overhauser Magnetometer/Gradiometer System
GSM-19 Overhauser Magnetometer
Features of the magnetometer
General magnetometer description
Sensitivity = 0.02 nT
Absolute Accuracy = 0.2 nT
Sample Rates up to 5 Hz
Low Power Consumption
"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.
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
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
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.
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
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
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: -40Â°C to +60Â°C
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
Walking Mag: Time, date and reading stored at coordinates of
Remote Control: Optional remote control using RS-232
Input/Output: RS-232 or analog (optional) output using 6-pin
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: -50Â°C to +60Â°C
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.
Performance Parameters: Resolution 0.5% and range to Â±200%
of total field. Frequency 15 to 30 kHz.
Dimensions and Weights
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
Dimensions and Weights: 93 x 143 x 150mm and weighs only
Console: 223 x 69 x 240mm
Sensor: 170 x 71mm diameter cylinder
Sensor and Staff Assembly: 2.0kg
GSM-19 magnetometer console, harness, battery charger,
shipping case, sensor with cable, staff, instruction manual, data transfer cable and
GSM-19 overhauser magnetometer
GPS Log Option
Memory Upgrade per 512
Walking Mag Option
GSM-19 Shallow Marine Fish
Equatorial Sensor Option