Apparent Resistivity
Definition
The resistivity value computed from a measurement assuming the ground is homogeneous. In practice the ground is layered and variable, so apparent resistivity is an integrated response; changes in it across a survey grid indicate underlying contrasts.
- Field
- Geophysical survey (magnetometry and earth resistance)
- Assumption
- Computed as if the ground is homogeneous
- Real ground
- Layered and variable, so value is an integrated response
- Forensic use
- Contrasts across a survey grid can indicate buried disturbances
Common questions
Why is a grave or buried object detectable through apparent resistivity even though the ground isn't really uniform?+
A disturbed area such as backfilled soil typically differs in moisture retention and compaction from the surrounding undisturbed ground, so it produces a measurable local contrast in apparent resistivity even though the underlying calculation assumes homogeneity.
Does a single anomalous apparent-resistivity reading confirm a burial at that spot?+
No. Natural variation such as buried rock, tree roots, drainage differences, or old services can also create contrasts, so a resistivity anomaly is treated as a target for further investigation, such as targeted excavation or corroboration with another geophysical method, not as confirmation on its own.
Related terms
- FEM (Frequency-Domain EM)
- A class of instruments that measure ground conductivity from above-surface, without electrode contact, by inducing eddy currents with an oscillating EM field....
- Fluxgate Gradiometer
- An instrument that measures the vertical gradient of the Earth's magnetic field using two fluxgate sensors mounted on a staff at fixed...
- Magnetic Susceptibility
- A measure of how strongly a material is magnetised by an external field. Topsoil heated by fire or biological activity has elevated...
- Twin-Electrode Resistivity
- A resistivity configuration using one mobile pair of contact electrodes and one remote pair. Current is injected and the voltage drop across...
- Wenner Array
- A four-electrode resistivity configuration where all four electrodes are equally spaced. Depth of investigation is approximately equal to the electrode spacing. Provides...