gssi.jpg (5542 bytes)


Multiple Frequency Electromagnetic Profiler

GEM300 - CloseupThe revolutionary design of the GEM-300 allows this frequency domain, electromagnetic profiling system to be configured to simultaneously measure up to 16 user-defined frequencies between 330 Hz and 20,000 Hz with fixed coil separation. By acquiring multiple frequencies the user can select the frequency(ies) which provide the best results for a specific application. Both in-phase and quadrature measurements are recorded. Output is the mutual coupling ratio (Q) in parts/million (ppm) or apparent conductivity in mS/m.

All survey acquisition parameters and EM data are stored on internal memory. Files are structured for simple download to a PC for immediate presentation on commercial mapping software packages.

The GEM-300 is lightweight, portable and easy to use which makes it ideal for use in the fields of:

  • Geology
  • Environmental Assessment
  • Engineering
  • Archaeology


GEM-300 in the field


GEM 300 data This data was collected using the GEM-300 set at 15,210 Hz in-phase, in horizontal dipole mode. The data shows two 55-gallon drums (top drum buried vertical, 18 inches deep; bottom drum buried horizontal, 34 inches deep).

A paper was published in the August 1996 issue of the Journal of Environmental & Engineering Geophysics (JEEG) entitled, "GEM-2: A new Multifrequency Electromagnetic Sensor." The ABSTRACT of the paper follows:

A new broadband electromagnetic sensor, GEM-2, has been tested at several environmental sites for subsurface investigation. A hand-held, digital, multi-frequency sensor based on an earlier, similar helicopter-towed sensor, GEM-2 operates in a frequency range of 90 Hz to 22 kHz, and can transmit an arbitrary waveform by means of the pulse-width modulation technique. Owing to the arbitrary nature of its broadcast waveform and high-speed digitization, the sensor can operate either in a frequency-domain mode or in a time-domain mode.

Depth of exploration for a given earth medium is determined by the operating frequency. Therefore, measuring the earth response at multiple frequencies is equivalent to measuring the earth response from multiple depths. Hence, such data can be used to image a 3-D distribution of subsurface objects. Results from several environmental sites indicate that the multifrequeny data from the GEM-2 is far superior in characterizing buried, metallic and non-metallic targets to data from conventional single-frequency sensors."



Measurement Values: I & Q values in either mS/m or ppm
Coil Spacing: 1.3 m
Operating Frequencies: 330 to 20,000 Hz
Power: Rechargeable NiMH batteries
Display: 62.5 x 43.5 mm LCD
Memory: 112,000 measurements (In-phase and Quadrature)
Measurement Range: Conductivity: 0.1 - 1000 mS/m
Length: 190 cm (74 in.)
Maximum width: 20 cm (7.9 in.)
Maximum height: 15 cm (5.9 in.)
Weight: 6.4 kg (14 lbs.)