The GEM-2 transmits electromagnetic signals into the ground and measures the returning secondary electromagnetic field. The response is recorded as in-phase and quadrature components, which can be used to calculate apparent conductivity and magnetic susceptibility.

The GEM-2 is a handheld, digital and programmable broadband electromagnetic sensor from Geophex. It can collect measurements at multiple frequencies, allowing surveyors to investigate different subsurface responses and depths.

Yes. Groundwater investigations are one of the applications identified for the GEM-2. Electromagnetic conductivity measurements can help identify variations associated with subsurface water and changes in geological materials.

Yes. The GEM-2 can be used to investigate subsurface variations relevant to geotechnical and engineering projects, including changes in soil properties and conductivity.

Yes. Environmental applications include mapping variations in soil conductivity and investigating areas potentially affected by contamination. The multi-frequency capability can provide additional information about changes with depth.

Yes. Electromagnetic induction surveys can identify variations in soil conductivity and magnetic susceptibility associated with archaeological features. The GEM-2 can therefore complement other archaeological geophysical techniques such as magnetometry and GPR.

Yes. The GEM-2 can respond to conductive and magnetic anomalies associated with buried metallic objects and infrastructure. It can therefore be useful for investigations of underground facilities, buried objects and contaminated sites. The response depends on the object’s size, material, depth, orientation and the surrounding ground conditions.

The system records in-phase and quadrature responses in parts per million (ppm). These measurements can be used to derive apparent electrical conductivity and magnetic susceptibility. Power-line noise can also be monitored as part of the survey data.

Different frequencies provide different responses to the subsurface. Generally, lower frequencies can investigate deeper, while higher frequencies provide greater sensitivity to shallower features. Using multiple frequencies therefore provides additional information about subsurface conditions.

Yes. Multiple frequencies can be acquired during a survey. In practice, Geophex recommends using around 3–5 frequencies for many GEM-2 applications, as increasing the number of frequencies can reduce signal-to-noise ratio.

The current GEM-2 provides a broad operating bandwidth of approximately 300 Hz to 96 kHz, allowing users to select frequencies appropriate to the survey objective and ground conditions.

Yes. JBUAS supplies specialist geophysical survey equipment and can advise on the GEM-2 configuration and accessories required for archaeological, environmental, geological and geotechnical applications. Need advice on electromagnetic surveying?
Contact JBUAS to discuss the GEM-2 and identify the most appropriate frequencies, survey configuration and data-processing workflow for your project.

Rapid data collection makes it suitable for efficiently surveying relatively large areas. GPS integration also allows measurements to be georeferenced during acquisition.

The GEM-2 has historically been supplied with WinGEM software for data management and positioning. Data can also be exported for processing and analysis using other specialist geophysical and GIS software.

Yes. The GEM-2 can form part of a wider geophysical survey strategy alongside UAV-mounted magnetometers, GPR and other sensors. The most appropriate combination depends on the survey objectives and accessibility of the site.

No. The GEM-2 is an electromagnetic induction (EMI) sensor, not Ground Penetrating Radar. GPR detects reflected radar signals, whereas the GEM-2 measures the subsurface electromagnetic response. The two technologies can complement each other in a wider geophysical survey.

Frequency selection depends on the target, expected depth, ground conditions and level of electromagnetic noise.

Yes, but electromagnetic interference from power lines, electrical equipment and other sources should be considered when planning a survey. The GEM-2 can monitor power-line noise, and frequency selection can be adjusted to reduce interference.

Yes. The sensor supports horizontal coplanar (HCP) and vertical coplanar (VCP) configurations. The selected orientation affects the instrument’s response and depth of investigation.

The system uses a 12 V rechargeable battery. Battery life depends on operating conditions and configuration; published specifications indicate approximately eight hours under normal survey conditions for earlier configurations.

Yes. The GEM-2 is designed as a portable, handheld system. Its sensor boom incorporates the sensing elements and electronics, with a detachable user interface and shoulder strap for field operation.

The sensor boom weighs approximately 2 kg. Complete system weight varies according to the electronics, battery and accessories supplied. Earlier GEM-2 specifications list a complete system weight of approximately 4 kg.

The sampling rate is selectable, with the system supporting approximately 25 or 30 measurements per second, depending on the configuration and operating environment.

The GEM-2 can use external GPS positioning or, where GPS is not being used, survey positioning can be established using dead reckoning/interpolation.

Yes. The GEM-2 can accept real-time GPS input, allowing survey measurements to be associated with geographic positions.