Using magnetometers for archaeology

Archaeologists are increasingly looking at remote sensing methods as techniques to explore sites with minimum disruption to the surroundings. This work is delivering new means of mapping prehistoric and historic sites in three dimensions rather than traditional two-dimensional methods.

Magnetics is a primary remote sensing technique that offers both ease-of-use and cost-efficiency.
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​The main benefits lie in the ability to resolve details non-invasively, the wide range of artifacts and cultural objects that are detectable, and the low-cost of magnetics in comparison to other methods.

Non-magnetic towed cart, showing 2 potassium sensors. Up to 10 sensors can be deployed with this vehicle.

​Magnetometry and gradiometry resolve many structures, including buildings, cooking sites, furnaces used for smelting, burial grounds, and other types of buried subsurface objects. 

Data is typically acquired using a gradiometer – a two-sensor configuration that serves to reduce natural noise from sunspot activity (diurnal effects) as well as focusing the depth of investigation to the near-surface. Depths of penetration vary up to 10m depending on the type of target being investigated (i.e. highly ferrous as opposed to weakly ferrous).

Case Studies

A number of case histories are available from Symetrics and GEM. Note that these case histories have been digitized and appear with less resolution as compared with the originals. However, they still provide numerous examples of the application of magnetics to archaeological investigations. 

Instruments and Data Processing Overview

Several different types of instruments are available for measuring a) total magnetic field (i.e. systems from Symetrics and GEM) and b) three components of the magnetic field (i.e. fluxgate systems). Total field systems offer a number of benefits over fluxgate systems, including high rates of acquisition and no requirement to calibrate systems during surveys for greater survey efficiency.

Processing of data is straight-forward, requiring a) downloading of magnetic and gradiometric data from the instrument to a personal computer and b) minor filtering for noise suppression related to geologic or other effects not of interest to the archaeologists. Simple software packages are available for these purposes from Symetrics and GEM.

Advanced users may also be interested in applying routines, such as Analytic Signal processing to convert dipolar total field anomalies to single peak anomalies that can be easier to visualize. Other advanced routines, such as modeling to determine the depth of magnetic sources, can also be applied.

Archaeologists work in some of the most diverse terrains possible. From the world’s largest historic site at Angkor Wat to the Indigenous burial grounds in North America to the ancient Roman fortifications that cover Europe, archaeologists are “breaking new scientific ground” every day. Our magnetometer has aligned its product offerings to meet these demanding requirements with instruments that are non-intrusive to the sites under study.
It's very high sensitivity optically pumped Potassium system is capable of resolving the most subtle contrasts in materials (such as those of clay bricks in soil).
The unique Overhauser system has a wide range of “detectability” for low contrast and high contrast (ferrous) structures while matching specifications of optically pumped Cesium instruments at a much lower cost.
And where economy is required, Symetrics also offers the world’s most feature-rich Proton Precession instrument – a tool with a classic value that complements any archaeologist’s toolkit.