19 articles
Airborne electromagnetic survey
An airborne electromagnetic survey is a geophysical method in which aircraft carry or tow electromagnetic transmitters and receivers to map ground conductivity, first tested in Canada in 1948.
Apparent resistivity
Apparent resistivity is the resistivity a subsurface would have if it were homogeneous and isotropic, computed from DC survey measurements and inverted to recover a true resistivity model.
Chargeability
Chargeability is a dimensionless measure of how strongly a rock or soil stores electric charge reversibly, the principal parameter of the induced polarization geophysical method.
Controlled-source electromagnetics
Controlled-source electromagnetics (CSEM) is a geophysical exploration method that maps subsurface resistivity using a controlled low-frequency source, used commercially to detect offshore oil and gas reservoirs.
Electrical resistivity imaging
Electrical resistivity imaging, also called electrical resistivity tomography (ERT), is a geophysical method that maps subsurface resistivity by injecting current and measuring voltage, used to find groundwater, contaminants, and geology.
Electrical resistivity method
The electrical resistivity method is a geophysical surveying technique, originating in the 1910s, that injects current into the ground to map groundwater, salinity, fractures, and contaminants.
Electrical resistivity tomography
Electrical resistivity tomography (ERT) is a geophysical imaging method that reconstructs subsurface electrical resistivity from electrode measurements, producing 2D sections and 3D volumes for hydrogeology, geotechnics, and environmental studies.
Electromagnetic tomography
Electromagnetic tomography is a geophysical method that reconstructs subsurface electrical conductivity from electromagnetic field measurements made at the surface, in boreholes, or from the air.
Geomagnetically induced current
A geomagnetically induced current (GIC) is an electric current driven through long conductors such as power lines by geomagnetic storms; it caused the 1989 Québec blackout.
Induced polarization
Induced polarization is a geophysical method measuring the delayed voltage decay of subsurface materials after an injected current is cut off, reporting chargeability and phase, used mainly to explore for disseminated metallic sulfides.
Magnetotellurics
Magnetotellurics is a passive geophysical method that uses natural electric and magnetic field variations to image subsurface electrical conductivity from hundreds of meters to hundreds of kilometers deep.
Membrane polarization
Membrane polarization is a mechanism of induced polarization in rocks and soils, in which clay surfaces and narrow pores form ion-selective zones that build up charge-storing ion concentration gradients.
Metal factor (geophysics)
The metal factor (MF) is an induced polarization parameter in geophysics, defined as percent frequency effect or chargeability divided by resistivity, with units of conductivity.
Resistivity meter
A resistivity meter is a geophysical field instrument that injects electric current through electrodes and measures voltage to determine subsurface resistivity, supporting groundwater exploration, mineral prospecting, and archaeology.
Schlumberger array
The Schlumberger array is a four-electrode configuration for measuring the electrical resistivity of the ground, with closely spaced potential electrodes, and the most common configuration for vertical electrical sounding.
Square array (electrical resistivity)
The square array is a four-electrode resistivity surveying configuration introduced by Habberjam and Watkins in 1967, used chiefly to detect the directional fabric of fractured bedrock.
Surface conductivity (geophysics)
Surface conductivity in geophysics is an extra electrical conductivity of porous rock or soil that flows along charged mineral surfaces rather than through pore water, and ignoring it biases resistivity interpretation in clays and shaly sands.
Transient electromagnetic method
The transient electromagnetic method (TEM), also called time-domain electromagnetic or TDEM surveying, maps subsurface conductivity from the decay of induced electromagnetic fields after transmitter turn-off.
Vertical electrical sounding
Vertical electrical sounding (VES) is a surface geophysical method that measures subsurface resistivity at increasing electrode spacings, producing a one-dimensional resistivity-versus-depth profile used mainly for groundwater prospecting.