Magnetic survey

Magnetic survey (prospection) is a technique used for the measurement of the earth's magnetic field aimed at identifying variations attributable to archaeological structures below the surface. Magnetic survey is performed with an instrument called a proton magnetometer. Many materials used in man-made artifacts are highly magnetic in relation to materials which occur naturally. For example, the clay used to make bricks and pottery has little if any magnetism. Once baked, however, the clay becomes highly magnetic through heating. After cooling, the material retains its new magnetic value, which remains locked in place for hundreds or even thousands of years. In magnetic survey, the same technique is used as that which is employed in electric survey: the surveyor takes a series of points on a well-defined grid and records the results. The man-made structures, if present, stand out against the naturally occurring features of the subsurface. For more information, see the Archaeological Prospection page of Bradford University. In the illustration on the right, you see Dr. Veronese and Dr. Roberti performing magnetic prospection at Horace's Villa in September, 1997.