Archaeology & Heritage
Geophysical Surveys
Magnetometry
Magnetometers and magnetic susceptibility meters are widely used in archaeological reconnaissance to rapidly identify subsurface features associated with past human activity. These non-intrusive techniques provide an efficient means of assessing large areas and targeting areas of archaeological potential.
Our detailed magnetometer surveys typically employ a 0.5 m traverse interval, where site conditions allow, producing high-resolution datasets capable of clearly identifying subtle magnetic anomalies beneath the ground surface. This approach enables the detection of a wide range of buried archaeological features, including cut features such as ditches and pits, field systems, trackways, and palaeochannels. Fired features, including hearths and ovens, as well as concentrations of ferrous material, can also be identified.
For larger areas, magnetic susceptibility sampling can be undertaken at wider intervals, commonly 10 m or 20 m. This reconnaissance-level approach highlights zones of enhanced magnetic response, which can then be targeted for more detailed magnetometer survey, allowing resources to be focused efficiently and effectively.
Ground Penetrating Radar (GPR)
GPR is a highly versatile geophysical technique suitable for a wide range of archaeological applications, performing effectively across both greenfield sites and hardstanding surfaces. GPR provides real-time subsurface imagery, displayed as vertical radar profiles (radargrams). Alternatively, data collected across an orthogonal grid can be post-processed to produce horizontal time-slice visualisations, supporting detailed interpretation and analysis.
GPR data provides valuable depth information for potential subsurface targets, making it an effective standalone method or a complementary technique for investigating anomalies identified through other geophysical methods, such as magnetometry or electromagnetic conductivity.
When using mid- to low-frequency antennas, GPR is capable of detecting a broad range of buried archaeological and structural features. These include walls, foundations, cut features such as ditches and graves, roads, tracks, voids, and buried military infrastructure. GPR is also effective in identifying features associated with historic gardens and broader anthropogenic modifications to the landscape.
For near-surface investigations, high-frequency GPR is particularly well suited to the examination of built heritage assets. This includes the investigation of walls, floors, and subsurface features within churches, cathedrals, and domestic buildings. High-frequency surveys can assist in the identification of under-floor burials, crypts, voids, chimney flues, and former doorways, providing valuable information while avoiding intrusive intervention.
Earth Resistance
Earth resistance surveys are a well-established geophysical technique for mapping buried stone-built features such as walls, buildings, cists, and roads. The method is also effective at identifying more conductive features, including pits, ditches, and graves, which contrast clearly with surrounding soils.
Earth resistance surveying is a versatile approach that can be deployed as a standalone technique in areas dominated by buried masonry, or as a complementary method to target anomalies identified through magnetic assessment. In particular, earth resistance surveys are highly effective within churchyards and burial grounds, where they can assist in identifying subsurface features while minimising disturbance.
Electromagnetic Ground Conductivity (EM)
Fixed-frequency electromagnetic surveys are an effective geophysical technique for detecting a wide range of buried features, including structural remains, ditches, former paths, and trackways. The in-phase component of the survey is particularly sensitive to metallic objects and effectively functions as a metal-detection response, supporting the identification of ferrous and non-ferrous material.
Electromagnetic surveys operate using electromagnetic induction to measure variations in subsurface electrical conductivity. As the technique does not require direct contact with the ground, it offers clear advantages over earth resistance surveying in environments where surface conditions restrict electrode insertion, such as hardstanding or sensitive ground surfaces.
EM instruments commonly used for archaeological survey typically provide effective depth penetration in the range of approximately 0.7 m to 1.5 m when operated in horizontal and vertical dipole configurations. This makes them well suited to the detection of shallow archaeological features and zones of disturbance.
For deeper investigations, larger EM instruments capable of penetrating to depths of approximately 3 m to 6 m can be employed. This increased depth range is particularly beneficial for identifying substantial or deeply buried features such as defensive ditches, large structural remains, or military bunkers, across both greenfield and hardstanding environments.
Time-domain electromagnetic instruments function as high-resolution metal detection systems capable of locating both ferrous and non-ferrous targets at depths exceeding 3 m below ground level, depending on the size, composition, and volume of the target material. This technique is especially valuable for investigations of military sites, including the detection of downed aircraft and associated ordnance, where deeper penetration and enhanced metal sensitivity are required.
