All materials exhibit a property called magnetic susceptibility, which is a measure of how magnetised the material becomes under the influence of an external magnetic field. If an object made from a material with a high magnetic susceptibility is placed in a uniform magnetic field then it will become magnetised and the magnetic flux will be concentrated in the area around the object.
This will cause an increase in the strength of the magnetic field close to the object and a corresponding weakening of the field at some distance away from the object. The presence of materials in the soil with dissimilar magnetic susceptibility will, under the influence of the geomagnetic field, create local variations in the strength of the magnetic field where this contrast in magnetic susceptibility occurs. A kiln or ferrous material may have an associated remanent field that will also give rise to local distortions of the magnetic field.
A magnetic gradiometer survey data with interpretation
Magnetic Gradiometer Survey
Applications: Magnetometry is ideal for archaeological prospection and the location of unexploded ordnance (UXO), waste drums, pipelines and cables.