08/06/2026
Electrical Tomography
What it is
Electrical Resistivity Tomography (ERT) is a geophysical technique used to reconstruct the distribution of subsurface resistivity along a profile.
It works by injecting electrical current into the ground and measuring the resulting potential, using an automated sequence of electrodes placed along a line or a grid.
CC ERT (Continuous Current)
This is the “classic” form of electrical tomography.
A multielectrode cable and closely spaced stakes are used: the system injects direct current into one pair of electrodes and measures the voltage on another pair.
Repeating this sequence automatically produces a set of apparent resistivity values at different depths.
The output is a 2D model of the subsurface, which can be extended to 2.5D by combining parallel profiles.
(DC-ERT with a max. of 32 electrodes can be performed using RM1 and related accessories)
AC ERT (Alternate Current)
The most recent evolution of the method uses a sinusoidal alternating current with adjustable frequency: this is the technology adopded from the very beginning by PASI Polares systems.
This approach allows for much faster acquisitions with large number of electrodes, reducing measurement time dramatically—often by a factor of ×10–20 compared to DC.
With a single measurement, both resistivity and induced polarization response can be obtained, increasing the amount of useful information.
AC tomography enables 2D, 3D and 4D configurations, depending on the number and arrangement of electrodes.
(In PASI product range, AC-ERT is now performed using Polares32.)
When ERT is used
• Geological and geotechnical investigations
• Stratigraphy reconstruction and detection of discontinuities
• Analysis of cavities, fractures, lithological variations
• Hydrogeological studies (saturated vs unsaturated zones)
• Environmental monitoring programs
• Mapping of backfills, landfills, altered volumes or contaminated areas
• Assessment of civil works and foundation soils
Electrical tomography is one of the most complete non-invasive methods for reading the subsurface, offering high resolution and excellent reliability in a wide range of applications.
Find more 👉 https://www.pasisrl.it/c/en/ert/electrical-resistivity-tomography
