Portable Ground VLF System - GSM-19V

Supplied By: GEM Systems, Canada

GEM's GSM-19V: Portable VLF System

The GEM GSM-19V portable VLF system is a robust tool for environmental and exploration purposes.

Technically Superior

This new evolved system builds off our proven airborne technology. The GEM VLF takes true measurements of the Vertical in-phase & Out-ofphase components as % of total field within the VLF frequency range of 15 - 30kHz. Many older systems only measure the total field and quadrature components of the field. Like the airborne system it features a 3-coil sensor and can acquire data from up to 3 VLF transmitting stations simultaneously without sensor orientation.

The GSM - 19V also has a correction for the tilt level of the VLF sensor for up to 10° from the horizontal plane.

Magnetometers and Gradiometers

About - VLF

The VLF-EM survey method is a passive electromagnetic system that utilizes distant, globally positioned, transmitters broadcasting at frequencies in the range of 15kHz and 30kHz. (in some cases a private/custom transmitter may be utilised in regions with sparse transmitters) In a VLF investigation, the magnetic field components of the transmitted signal, which are effected by local ground conditions, are measured.

GSM-19V VLF Applications:

    • Resistivity imaging and bedrock mapping

    • Delineate contrasts in conductivity at depth

    • Map geological contacts, faults

    • Search for mineralized bodies

    • Water exploration

GEM/EMTOMO - VLF Resistivity

GEM uses the VLF2DMF Software platform created by EMTOMO TM. This program provides 2D inversion of multi-frequency VLF-EM data.

Magnetometers and Gradiometers

The package includes a map module for display of the survey, the selection of profiles for inversion and displays the survey results. The program can also be used for modeling studies. The user can build a complex resistivity model and calculate its VLF-EM response. Features include;

    • 2d resistivity sections

    • Resistivity depth plan slices

    • Forward Modeling

    • Fraser Filter

    • Karous-Hjelt Filter (current density sections)

The inversion procedure used in VLF2DMF is two-dimensional (2-D) and is based on the Occam technique (e.g. DeGroot and Constable 1990, Sasaki 1989, Sasaki 2001).The forward modelling of VLF2DMF program is based on the finite-element method.

Why Use VLF

VLF surveying has been utilised since 1964 as a rapid means to find large linear conductive features to provide information about the subsurface for geological mapping. Large area surveys have provided regional structural information but due to a lack of quantitative information such as depth to structure information the method had been marginalised until quite recently. In 2007, the Geological Survey of Sweden demonstrated that not only could VLF data be rapidly and efficiently collected it could provide excellent structure and resistivity information to depths of 100 m and theoretically to over 200 m.

Advances in both technology to collect VLF data properly and advances in computer technology and mathematical inversion techniques have provided the industry with a new cost-effective means for imaging the top 100 metres of the earth.

The robust GEM multi frequency GSM 19V VLF system, provides the user with a practical way to collect meaningful resistivity information in a very cost effective manner. In addition, the VLF system can be easily combined with GEM magnetometers for additional subsurface insight.


VLF Parameter Specifications
Frequency: Up to 3 stations between 15 & 30.0 kHz
Parameters: Vertical in-phase and out-of-phase components as % of total field
2 components of horizontal field amplitude
Total field strength in pT
Resolution: 0.1% of total field for VLF fields of 5 pT or stronger
Operating Temperature: -40°C to +50°C
Dimensions: Sensor: 14 x 15 x 11 cm
Console: 22.3 x 6.9cm x 2.4 cm
Weights: Sensor: 1.0 kg
Console with Belt: 2.1 kg
Storage: Automatic with: time, coordinates, slope, EM field, frequency, in- and out-of-phase vertical, and both horizontal components for each selected station
Input/Output: RS-232 output using 6-pin weatherproof connector with USB adapter
Data Export: Standard XYZ (i.e. line-oriented) format for easy use in standard commercial software programs

GSM-19V Supply:

GEM VLF systems can add either single or multi-sensor Magnetometer capability or can be added to existing Magnetometer systems to provide a truly robust exploration solution

The GSM-19V units come complete with an industry leading three year warranty

Available Options:

    • VLF2DMF software by EMTOMO Standard GPS Option B:

        • 0.7 SBAS (WAAS, EGNOS, MSAS)

    • High resolution GPS Option D:

        • 0.6m SBAS (WAAS, EGNOS, MSAS)

        • 0.6m OmniStar (VBS2 subscription)

Magnetometers and Gradiometers


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