Electrical Resistivity Imaging
Also referred to as an ERT survey, this method measures subsurface resistivity to generate 2D or 3D models of material variation, supporting stratigraphic interpretation and groundwater assessment.
Electrical and electromagnetic geophysical survey methods measure variations in resistivity and conductivity to map subsurface materials, void features and contamination. These methods support geotechnical, environmental and infrastructure investigations across a wide range of site conditions.
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What are Electrical & Electromagnetic Methods
Electrical and electromagnetic geophysical survey methods work by measuring how well subsurface materials conduct or resist an electrical current. Different materials, whether rock, soil, water, voids or contamination, have distinct electrical properties. By mapping those contrasts, these techniques build a picture of what lies beneath the surface without intrusive investigation.
Electrical resistivity imaging or Electrical Resistivity Tomography (ERT) is the most widely applied resistivity survey method. An ERT survey produces a continuous 2D or 3D model of subsurface resistivity, making it effective for bedrock definition, groundwater and contamination mapping, karst void detection and geotechnical investigation, particularly where density inversions are present. Where discrete depth profiles are needed, such as earthing grid design, vertical electrical sounding provides a targeted alternative.
Electromagnetic survey methods measure conductivity responses from the surface without requiring direct ground contact. Frequency domain electromagnetics is well suited to near-surface contamination mapping geophysics and landfill investigations. Time domain electromagnetics extends that capability to greater depths. Induced polarisation surveys add a further dimension by detecting the chargeability of subsurface materials, useful for distinguishing lithologies that produce similar bulk resistivity responses.
The Value of Electrical and Electromagnetic Survey Methods.
Electrical geophysical survey methods are non-invasive and can cover large areas efficiently, making them a practical first-pass tool before drilling or intrusive works. The continuous subsurface models produced by electrical resistivity imaging reduce interpretive uncertainty across a site, rather than relying on point data from boreholes alone.
These methods are also versatile. A single electrical or electromagnetic geophysical survey program can address groundwater mapping, contamination screening and geotechnical objectives simultaneously. Where the investigation scope demands it, electrical methods integrate readily with seismic and other geophysical techniques. That flexibility, combined with direct integration with drilling and ground truthing, makes resistivity and electromagnetic survey methods a cost-effective component of most site investigation programs.
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Applications
- Groundwater mapping geophysics and aquifer delineation
- Contamination mapping geophysics and landfill investigations
- Karstic topography and void delineation
- Geotechnical and site investigation
- Environmental assessments and monitoring
- Infrastructure and land development planning
- Salinity and soil variability mapping
- Dam and embankment investigations
- Integration with drilling and ground truthing
Methods Included
Vertical Electrical Sounding
A targeted resistivity survey used to estimate depth variations in subsurface layers, commonly applied for earthing grid design.
Frequency Domain Electromagnetics
An electromagnetic survey method that measures conductivity variations to rapidly map near-surface conditions and identify contamination, landfill extents or salinity.
Time Domain Electromagnetics
Time domain electromagnetics is a technique used to investigate deeper subsurface conditions, effective for mapping resistive and conductive targets where surface-based resistivity methods have limited depth penetration.
Induced Polarisation Survey
Measures chargeability alongside resistivity, typically run in combined mode to support conductive target mapping and improve subsurface discrimination where resistivity alone is insufficient.
FAQs
Electrical resistivity imaging is a type of electrical geophysical survey that measures how strongly the ground resists electrical current. By analysing these variations, an ERT survey can produce detailed images of subsurface conditions.
An electromagnetic survey uses electromagnetic fields to measure subsurface conductivity. These electromagnetic geophysics methods are commonly used for mapping soil variation, salinity, groundwater and contamination.
An Electrical Resistivity Tomography (ERT) survey is a type of electrical resistivity imaging that measures variations in subsurface resistivity to produce detailed 2D or 3D models of the ground. ERT surveys are commonly used for geotechnical investigations, groundwater mapping, contamination assessments and bedrock or void delineation.
Electrical geophysics is the use of electrical and electromagnetic methods to investigate subsurface conditions by measuring variations in resistivity and conductivity. These non-invasive techniques are widely used to support geotechnical, environmental and groundwater investigations by mapping changes in geology, moisture, contamination and other subsurface features.
Induced polarisation (IP) is an electrical geophysical method that measures the ability of subsurface materials to temporarily store an electrical charge. It is commonly used alongside electrical resistivity imaging to improve the discrimination of subsurface materials where resistivity alone cannot distinguish between similar geological units.
Electrical resistivity imaging involves direct current injection into the ground, while electromagnetic survey methods are inductive and do not require ground contact. Both are complementary electrical geophysical survey techniques.
Yes. Both electrical resistivity imaging and electromagnetic survey methods are widely used for groundwater mapping geophysics and contamination mapping geophysics, identifying variations in moisture and conductivity.
Depth of investigation depends on the method and survey configuration. This can range from 1 m to as deep as 100 m below ground level.  ERT survey and time domain electromagnetics can investigate deeper conditions, while frequency domain electromagnetics is typically focused on near-surface mapping. It’s important to note that resolution always decreases with depth of investigation. Typically, deeper investigations require a larger survey footprint at the surface.
To design an effective electrical geophysical survey, we require site location, access constraints, target depth and project objectives to determine the most suitable methods.
Deliverables include processed sections, interpreted models and integrated datasets from electrical resistivity imaging and electromagnetic survey data, tailored to project requirements.
Why GBG Group for Electrical and Electromagnetic Surveys
With over 30 years of experience in Australia, GBG delivers reliable electrical resistivity imaging and electromagnetic survey solutions, combining, a large equipment pool, technical expertise with practical project delivery.
Electrical and Electromagnetic Methods for Subsurface Imaging
Electrical resistivity imaging and electromagnetic geophysics provide non-invasive subsurface imaging, enabling detailed interpretation of geological, hydrogeological and environmental conditions.
Integration with Geotechnical and Environmental Investigations
These electrical geophysical survey methods are commonly integrated with drilling, laboratory testing and other geophysical techniques to improve confidence in subsurface models.
Applications for Groundwater and Contamination Mapping
These methods are widely used for groundwater mapping geophysics and contamination mapping geophysics, supporting environmental assessments and land development.
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