Magnetic Susceptibility

  Topsoil magnetic susceptibility survey can be employed to rapidly identify potential zones of archaeological activity, particularly areas subject to settlement or industry. The Bartington Magnetic Susceptibility instrument temporarily magnetises the ground by creating a low intensity, alternating magnetic field. It then measures the response. The susceptibility is measured in SI volume susceptibility units (x 10 ^-5 ). The usefulness of this system is confined to the top few centimetres of topsoil, but its wider range (measurement intervals of up to 30m) enables rapid coverage of large areas. This is, of course, at the expense of detailed resolution, and is recommended primarily as a preliminary prospecting technique used to highlight areas for detailed gradiometry. However, on sites where archaeological features have been completely ploughed out, magnetic susceptibility measurement may produce the only clear evidence of earlier activity.