Magnetic prospecting is based on the measurement of the Earth's magnetic field and its local variations caused by the presence of geological (or man-made) objects. These variations depend on the magnetic susceptibility of these structures and the total magnetic field.
Magnetic susceptibility is a material property that describes changes in the magnetization of an object under the influence of an external magnetic field, creating a disruptive secondary field. Magnetometers detect all objects with high magnetic susceptibility. Discrimination between objects of different dimensions is based on analysis of the amplitude and shape of magnetic anomalies.
Magnetic methods are frequently used to detect buried metallic contaminants, metal deposits and archaeological finds.