Sites of human occupation can be discovered and mapped magnetically where the right soil magnetic conditions are present. For example, where soils are disturbed or burnt the area affected can have a localised magnetic susceptibility value which is in contrast to the ambient value. Biological processes can also bring about magnetic alterations. Fired clays containing iron can acquire a high value of magnetic susceptibility and a thermo-remanent magnetisation.

The magnetic susceptibility of the top-soil surface can be mapped using the MS2 magnetic susceptibility meter and an MS2D loop sensor  to help delineate ancient field usage and boundaries. Vertical profiles of sub-surface magnetic susceptibility taken using the MS2H down-hole probe can assist in identifying occupation levels.

The magnetic gradiometer Grad601 is a survey instrument that detects disturbances in the geomagnetic field caused by the contrasts in magnetic susceptibility. It will also detect thermo-remanance in kilns and bricks. The depth of survey for the gradiometer can be typically 2 metres with a surface spatial resolution of down to 0.25 metres. Area coverage can be up to 3 to 4 hectares per day.