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GSMP-40 v6.0

Optically Pumped Potassium Magnetometer / Gradiometer / VLF

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New Generation Potassium System

A new generation of Potassium systems -- the highest sensitivity and absolute accuracy optically pumped magnetometers available. The new GSMP-40 system extends these characteristics to the next generation of even higher performance instruments.


The upgraded v6.0 system is the highest sensitivity and absolute accuracy magnetometer / gradiometer available. It is designed for specialized mobile and stationary applications that require the most demanding survey specifications.

Key technologies:
  • Integrated GPS option (the only system with fully built-in GPS)
  • 20 times per second sampling rate
  • “Walking” mode for acquisition of high density data
  • Enhanced memory (increased by 8 times to 4 Mbytes standard and expandable to 32 Mbytes)
  • Programmable base station (for scheduling base stations in one of three modes)
  • Optional DGPS real-time and post-time processing (for meter to sub-meter positioning accuracy)
  • Rapid data transfer (using the advanced GEMLinkW software)
  • Internet-based upgrades (from the office or field)
Major benefits:
  • Acquisition of very high resolution and accuracy data. Potassium systems are substantially more sensitive than other optically pumped magnetometers / gradiometers.
  • Location of very weakly magnetic objects or small-size anomalies. This is a key requirement in applications, such as UXO / EOD and archeology, where success depends on the ability to map and characterize the smallest contrasts in magnetic physical properties.
  • High quality results in areas with high gradients. New small diameter (40mm) sensors optimize magnetic measurements for sensitivity and gradient tolerance.
  • Proven reliability and predictability of results. The natural physics of Potassium narrow line spectra minimizes heading and orientation errors to negligible levels.
  • Minimization of maintenance costs. Once a system is purchased, there is no need to return it for periodic optical alignment. This significantly reduces servicing and shipping costs over the lifetime of an instrument.
  • Enhanced survey efficiency. The GSMP-40 minimizes operating requirements, such as warm up and lock times, that slow surveys down.
  • Fast response to changing magnetic fields - for moving and stationary work.
A Different Approach to Optically Pumped Technology

While some of the principles of Terraplus' unique optically pumped Potassium magnetometer are similar to other optically pumped systems, the Potassium approach differs significantly in terms of the underlying physics. The main difference is that Potassium is characterized by widely-spaced, non-overlapping spectral lines. Spectral lines provide the basis for measurement in all optically pumped systems. From an instrumentation perspective, narrow, non-overlapping spectra provide a number of benefits: Enable the electronics to easily lock on a pre-defined spectral line. This, in turn, translates into very high sensitivity and maximum bandwidth (i.e. the “size” of geophysical features that can be resolved with the system). Minimal heading errors. These errors occur due to variations in alignment of the sensor head in the magnetic field. With Potassium errors are less than 0.1 nT. With other optically pumped systems, the heading error is 1 to 2 nT and can completely overwhelm the real magnetic response. Reductions in heading errors also translate into improved gradient measurements. As indicated, the GSMP-40 does not introduce orientation “noise” into measurements. The result is that the gradient measurements are very high quality -- both in dynamic and static environments.

Advancing the Field of Potassium Magnetometry

Recent developments with small sensor designs have increased gradient tolerance by five times while maintaining the industry standard in sensitivity and absolute accuracy.

Theory of Operation

A typical alkali vapour magnetometer consists of a glass cell containing an evaporated alkali metal (i.e. alkali atoms). According to quantum theory, there is a set distribution of valence electrons within every population of alkali atoms. These electrons reside in two energy levels as represented by the numbers 1 and 2 in the figure below. Light of a specific wavelength is applied to the vapour cell to excite electrons from level 2 to 3 only. This process (called polarization) reduces the number of atoms with electrons at level 2. The result is that the cell stops absorbing light and turns from opaque to transparent. Electrons at level 3 are not stable and spontaneously decay back to levels 1 and 2. Eventually, level 1 becomes fully populated and level 2 is fully depopulated. At this point, RF de-polarization comes into play. Here, we apply RF power of a wavelength that corresponds to the energy difference between levels 1 and 2 to move electrons from level 1 back to level 2. The significance of de-polarization is that the energy difference between levels 1 and 2 (i.e. the frequency of the RF depolarizing field) is directly proportional to the magnetic field. The system detects the fluctuation of light intensity (i.e. modulation) as the cell becomes opaque and transparent, and measures the corresponding frequency. The frequency value is then converted to magnetic field units.


Performance (40 mm sensors)
Sensitivity:  < 0.002 nT
Resolution:  0.0001 nT
Absolute Accuracy:  0.2 nT
Dynamic Range:  20,000 to 120,000 nT
Gradient Tolerance:  Over 13,000 nT/m
Sampling Rate:  1 to 20 readings / sec
Operating Temperature:  -20C to +55C

Operating Modes

Manual: Coordinates, time, date and reading stored automatically at minimum 1 / sec and maximum 20 / sec intervals.
Base Station: Time, date and reading at same intervals as manual mode.
Remote Control: Optional remote control using RS-232 interface.
Input / Output: RS-232 or analog (optional) output using 6-pin weatherproof connector.

Storage - 4Mbytes (# of Readings)

Mobile: 209,715
Base Station: 699,050
Gradiometer: 174,762
Walking Mag: 299,593


Console: 223 x 69 x 240mm
Sensor: 145 x 65mm (ext.) cylinder
Electronics Box: 310 x 75 x 90mm

Console: 2.1 kg
Sensor and Electronics Box: 2.4 kg

Standard Components

GSMP-40 console, electronics box, GEMLinkW software, batteries, harness, charger, sensor with cable, 24V battery belt, RS-232 cable, staff, instruction manual and shipping case.

Optional VLF

Frequency Range: Up to 3 stations between 15 to 30.0 kHz
Parameters: Vertical in-phase and out-of-phase components as % of total field. 2 relative components of the horizontal field.
Resolution: 0.1% of total field