TThe GEM-2 Ski is a light weight (2kg), hand-held, digital, multi-frequency broadband electromagnetic sensor. It operates in a frequency range of 30 Hz to 93 kHz, and can transmit an arbitrary waveform containing multiple frequencies. The unit is capable of transmitting and receiving any digitally-synthesized waveform by means of the pulse-width modulation technique.
Because it is comfortable to carry and has a field-swappable battery, extended surveys are no problem. Its powerful transmitter and wide coil separation allow scanning to depths up to 10 meters, depending on soil conditions.
GEM-2 - Technical Specifications
The GEM-2 ski is designed to minimize the temporal drift in a different way from all other instruments. The GEM-2 ski contains three coils that are precisely maintained in their relative separations amongst each other. Any small changes in the relative separations can cause a shift (or drift) in the signal level.
The 3 coils within the ski are embedded in a composite structure made of synthetic materials chosen to have a low thermal expansion coefficient. Furthermore, the bucking action is set by the relative locations of the coils so any linear expansion does not affect the distance ratios, maintaining the bucking. Owing to its careful design and manufacturing, the GEM-2 ski has not shown any appreciable drift and diurnal temperature changes are not a significant factor.
The GEM –2 is suitable for investigations in:
The EM31-MK2 maps geologic variations, groundwater contaminants, or any subsurface feature associated with changes in ground conductivity using a patented electromagnetic inductive technique that allows measurements without electrodes or ground contact. With this inductive method, surveys can be carried out under most geologic conditions including those of high surface resistivity such as sand, gravel, and asphalt.
Ground conductivity (quad-phase) and magnetic susceptibility (in-phase) measurements are read directly from an integrated Allegro CX data logger. GPS data can also be collected in real time, which provides geo-referenced data sets. TrackMaker software running on the data logger enables the user to see real time and historic instrument track proving a useful tool for ensuring even data collection.
The effective depth of exploration is about about three metres (horizontal mode) or six metres (vertical mode), making it ideal for geotechnical and environmental site characterization. Important advantages of the EM31 over conventional resistivity methods are the speed with which surveys can be performed, the precision with which small changes in conductivity can be measured and the continuous readout and data collection while traversing the survey area. Additionally, the in-phase component is particularly useful for the detection of buried metallic structures and waste material.
More detailed information
The EM34-3 is a simple-to-operate, cost-effective instrument for the geologist and hydrogeologist alike; applications have been particularly successful for the mapping of deeper groundwater contaminant plumes and for the exploration of potable groundwater resources.
Using the same inductive method as the EM31, the EM34-3 uses three intercoil spacings - 10, 20 and 40 m - to provide variable depths of exploration down to 60 metres. With three intercoil spacings and two dipole modes (horizontal as shown, and vertical) at each spacing, vertical soundings can be obtained. In the vertical dipole (horizontal coplanar) mode, the EM34-3 is very sensitive to vertical geologic anomalies and, as a consequence, is widely used for groundwater exploration in fractured and faulted bedrock.
The EM34-3 includes a real time (RT) digital output enabling data to be logged to a ruggedised Allegro CX data logger. Data can be collected with GPS positioning for a geo-referenced data set.
The EM38 provides measurement of both the quad-phase (conductivity) and in-phase (magnetic susceptibility) components within two distinct depth ranges, all simultaneously, without any requirement for soil-to-instrument contact. With a maximum effective depth of exploration of 1.5 m, applications in agriculture, archaeology and general soil sciences are common.
The standard EM38 includes two receiver coils, separated by 1 m and 0.5 m from the transmitter, providing data from effective depth ranges of 1.5 m and 0.75 m respectively when positioned in the vertical dipole orientation, and 0.75 m and 0.375 m respectively when in the horizontal dipole orientation. The EM38 model includes one receiver coil only, at 1 m from the transmitter.
The EM16 VLF Receiver is the most widely used electromagnetic geophysical instrument of all time. Local tilt and ellipticity of VLF broadcasts are measured and resolved into inphase and quadrature components of VLF response. The EM16 has discovered several base and precious-metal ore bodies and many water-bearing fractures and faults.
The EM16R Resistivity Attachment uses a pair of electrodes to measure the apparent resistivity of the earth. The combined EM16/16R instrument can detect a second earth layer if the layer occurs within the VLF skin-depth. In addition, the EM16/16R can map resistive alteration for gold exploration.
