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A type of geophysical instrument used for magnetic surveys in which a pair of magnetometers are normally mounted one above the other on a single support staff. Various kinds are available, including proton gradiometers and caesium gradiometers, but the most commonly used in archaeology is the fluxgate gradiometer with the direction‐responsive sensors between 0.5 m and 2.0 m apart. This measures the gradient in a magnetic field and will detect shallowly buried features and structures. The use of dual sensors overcomes many of the problems associated with single‐sensor instruments, for example variations in the strength of the Earth's magnetic field and deep‐seated geological anomalies. By systematically scanning an area on a grid system and logging the readings at close intervals it is possible to build up detailed plots showing the shape and form of the archaeological anomalies. These can be used to propose the nature and extent of buried features.

Subjects: Archaeology.

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