Resistivity

Resistivity survey measures the electrical resistance of the earth’s soil moisture content. A twin probe resistance meter is normally used, which involves the pairing of electrodes (one current and one potential), with one pair remaining in a fixed position (remote probes), whilst the mobile probes measure resistivity variations across survey grids. Resistance is measured in ohms, and this method of archaeological prospection is generally effective to a depth of 1m.

Features such as wall foundations are usually identified as high resistance anomalies, as are rubble spreads, made surfaces (i.e. yards and paths) and metalled roads and trackways. In contrast, low resistance values are normally associated with water-retentive features such as buried ditches and pits.