Data are 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 Histories

A number of case histories are available from 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 on the application of magnetics to archaeological investigations. To access these case histories, click the links below: 

• Numerous case histories from Europe and the Middle East
• Integrated case history from North America

Instruments and Data Processing Overview

Several different types of instruments are available for measuring a) total magnetic field (i.e. systems from 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 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 depth to magnetic sources, can also be applied.

Note: For archaeologists considering applying magnetic methods, there are a range of programs that offer funding for instrumentation purposes. Users in the United States, for instance, may wish to consult the National Science Foundation for more information. Alternately, archaeologists from other countries can consult similar local funding agencies.

Applying Advanced Magnetic Technologies

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 cov er Europe, archaeologists are “breaking new scientific ground” every day. GEM has aligned its product offerings to meet these demanding requirements with instruments that are non-intrusive to the sites under study.

Its 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 much lower cost.

And where economy is required, GEM also offers the world’s most feature-rich Proton Precession instrument – a tool with classic value that complements any archaeologist’s toolkit.