Brochure (PDF)

The highest sensitivity total magnetic field measuring device ever developed.


The GSMP-20GS is the highest sensitivity total magnetic field measuring device ever developed. The GSMP-20GS produces 0.1 pT p-p sensitivity (0.0001 nT p-p) at a sampling rate of 20 Hz, averaged over a 1 second interval. The GSMP-20GS Potassium Supergradiometer is well over an order of magnitude more sensitive than any other gradiometer in existence. The GSMP-20GS was developed in response to the United State Geological Survey's (USGS) requirement for an ultra-high sensitivity magnetic gradiometer. It is in part the GSMP-20GS's larger sensors that provide sensitivities demanded by the ultra-sensitive gradiometer system. The GSMP-20GS operates on principles similar to other alkali vapour magnetometers, but benefits from the unique nuclear properties of Potassium.

The GSMP-20GS is comprised of:
  • rugged 3.5" x 19" rack-mountable chassis, containing ultra-high sensitivity gradiometer signal processor
  • LCD display & programmable RS-232 output port
  • External Potassium Lamp assembly
  • External sensor electronics assembly
  • two (2) GSMP-20GS spherical sensors, measuring 15 cm in diameter
The GSMP-20GS is fully compatible with AirNAV airborne data acquisition and navigation system.

Event of 0.0001 nT p-p recorded by GSMP-20GS Ultra-High Sensitivity Potassium SuperGradiometer
(object at 40 metres from GSMP-20GS sensor)


Some of the important benefits of the GSMP-20GS optically pumped supergradiometer include:
  • highest sensitivity ever developed 
  • best absolute accuracy
  • almost no orientation errors
GSMP-20GS Advantages
  • GSMP-20GS sensors have the highest absolute accuracy (varying by no more than ± 0.1 nT between sensors) critical for ultra-high sensitivity gradiometer measurements 
  • GSMP-20GS does not require regular calibrations
The long term stability, high sensitivity and fast response to the changing magnetic field make the GSMP-20GS ideal for a wide variety of applications, such as:
  • airborne magnetic gradient surveying
  • ordnance (weapons) detection 
  • shallow water marine craft monitoring
  • earthquake prediction
Additional Options
Specialized airfoil assemblies that can house up to four SuperGradiometer sensors capable of measuring magnetic gradient in up to three directions at once in airborne surveys.

Benefits of the nuclear properties of Potassium - Gradiometer Applications
  • absolute accuracy - the GSMP-20GS's unmatched absolute accuracy (a variance of only ± 0.1 nT between any GSMP-20GS sensors) is critical for ultra-high sensitivity gradiometer measurements.
  • sensitivity - inherent potential sensitivity results from the nuclear properties of potassium, is realized by exceptionally narrow spectral ESR lines of 0.1-0.15 nT
  • insensitivity to orientation - virtually zero heading error resulting from the nuclear properties of potassium
Theory of Operation

A typical alkali vapour magnetometer consists of a glass cell containing the evaporated alkali metal, which is exposed to light of a specific wavelength. According to quantum theory, in every population of alkali atoms, there is a set distribution of valence electrons between two energy levels, represented by 1 and 2 in the figure below.  A wavelength of light is applied to the cell to excite electrons only from level 2 to level 3. This is called polarization. As the number of atoms with electrons at level 2 decreases, the cell will stop absorbing light, and will turn from opaque to transparent.  Electrons at energy level 3 are not stable, and will spontaneously decay back to levels 1 and 2. Eventually, level 1 will become fully populated, and level 2 will become depopulated, and the cell will be completely transparent.  That's where RF depolarization comes into play. RF power of a wavelength that corresponds to the energy difference between levels 1 and 2 is applied to the cell to move electrons from level 1 back to level 2. The significance of this act is that the energy difference between levels 1 and 2 (the frequency of the RF depolarizing field) is proportional to the magnetic field.


Specifications of the GSMP-20GS Potassium SuperGradiometer

Resolution 0.001 pT for up to 20 readings per sec
Noise Envelope
0.02 - 0.2 Hz 0.02 pT rms
1 reading per sec 0.03 pT/vHz
Reading intervals 0.05, 0.1, 0.2, 0.5 & 1 sec (others optional)
Absolute Accuracy +/- 0.1 nT
Time base stability 0.01 ppm over –40ºC - +85ºC.
Long term stability 1 pT/day (aging 1 ppm per year)
Tuning Wideband system no tuning
Range 10,000 to 100,000 nT
Sensor Orientation 45º ± 35º off the magnetic field direction
Analog Output 1 channel of magnetic field & 1 channel of gradient
1, 10 & 100 pT. 1, 10, 100 nT & 1 mT (Selectable full scale)
Output Digital Output Serial RS232C with programmable parameters, Visual Output Alphanumeric LCD, 11 digit magnetic field, 7 digit magnetic gradient
Temperature Range -40º to + 55ºC
Console Dimensions & Weight 483 x 89 x 406 mm / 6.6 kg (19" x 3.5" x 16")
Sensor Electronics Console Dimensions & Weight 100 x 50 x 50 mm / 1.0 kg
Sensor Dimensions & Weight 26.3 cm dia. x 23 cm / 6.0 kg
Lamp Assembly 17 cm x 9 cm dia.
Cable Lengths User specified 1 - 300 m
Power Requirements Ex. input voltage 22-32V, 12W ave., 40 W max.

Ordering Information
Description Order Number
GSMP-20GS  4029-2000-GSsys