An Introduction to Gradiometry

An accomplished researcher, Danielle Kurin, PhD, is a former assistant professor and tenured associate professor of bioarchaeology at the University of California, Santa Barbara. In her research, Danielle Kurin has conducted isotope and trace element analyses, gross and microscopic analyses, bone density and biomechanics assessments, and histological assessments on ancient bone specimens. She is also proficient in various remote sensing and imaging techniques, including CT scanning, ultrasound, photogrammetry, and gradiometry.

A technique commonly used in archaeology, magnetic gradiometry involves mapping an environment for magnetized archaeological objects with the aid of special instruments called magnetometers. Normally, a combination of the magnetic field from the earth’s liquid core (which contains the magnetic metals nickel and iron) and magnetic mineral components of local rocks results in a vector (a magnetic field presence with a defined amplitude and direction) at any point on the earth’s surface. Any material that remains buried in the soil for a long period will become magnetized by the surrounding magnetic field if the material has an appreciable magnetic susceptibility. Once it is magnetized, the material itself will present an anomalous magnetic field that can be distinguished in contrast with the less susceptible host soil and sediments and thus detected.

Some examples of materials that can be detected in the soil using magnetic gradiometry are ancient walls, hearths, burnt remains, in-filled pits, and ferrous metals. To increase archeological survey speed and efficiency, gradiometers are used for surveys. A gradiometer is essentially a pair of magnetometers (bearing sensors) that are separated by distance. The extent to which a gradiometer can improve efficiency will depend on its configuration, sensor height, and necessary adjustments to the base station.