Magnetic Gradiometer (Geomagnetic)

Magnetic Gradiometer (Geomagnetic)

The geomagnetic method is used to measure components of the Earth’s magnetic field (vertical, horizontal, and total) or variations in the intensity of this field. These variations allow for the differentiation between magnetized and non-magnetized objects. The method is sensitive to variations in magnetic susceptibility (resulting from changes in induced magnetization) as well as the presence of thermoremanent or viscous magnetization. While remanent magnetization plays a negligible role in the detection of archaeological artifacts, thermoremanent magnetization is a primary factor. For instance, clay—a raw material for ceramics frequently found at archaeological sites—acquires magnetic properties during the processes of heating and cooling.

In geomagnetic surveys conducted as part of shallow geophysical investigations, the most significant factor is the variation in the magnetic properties of the soil. Many researchers have extensively studied the transformation of iron oxides—which alters the magnetic properties of soil—and the oxidation processes that drive these changes. Furthermore, the transformation of iron oxides resulting from bacterial reduction within the soil is also a subject of research. Additionally, it has been observed that certain rock units, due to their high iron oxide content, may undergo chemical alterations—sometimes referred to as “fermentation” in this context—which also contribute to the transformation of iron oxides. In general, materials such as clay, ceramics, or hearth structures that have been subjected to burning as a result of human activity acquire thermoremanent magnetization.