An electrical current is passed through the ground between the two electrodes in order to measure the resistance. It is more difficult for the current to pass through drier, more compact material, such as a buried wall of a house or an ancient road than it would be for it to pass through damp clay soil, which it would penetrate relatively easily.

The data collected is entered into a computer programme that produces an image of the land being surveyed. This image will indicate the presence of archaeological artefacts by shading them differently to the rest of the soil. More modern resistivity testing equipment will produce more accurate and detailed images, but this is expensive, and often not financially viable.

Polarisation is a common condition encountered whilst testing resistivity of a survey area. This produces erroneous reading, and to prevent its occurrence, four probes are required.

For Ground Survey’s to be conducted, again there are a variety of data collection techniques that archaeologists can use. The most advanced being Topography, but equally important are the less complicated methods of Planning and Mapping.Topography involves the recording of the surface character of an area. A theodolite is used to take readings of the ground, which are entered into a computer programme that then creates a 3D image of the site surface. It is often used with geophysical survey techniques to amalgamate the site surface image, with the sub-surface one. Planning and Mapping techniques are used to create a plan of the archaeological site. This plan can be scaled correctly so the accurate location if the archaeological features of interest can be determined by the entry of the data into a mapping package on a computer.

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