Ground Penetrating Radar

Although airborne radar has been in use for many decades, Ground Penetrating Radar (GPR), is a relatively new technique. Over recent years vast improvements have been made to both the hardware and software making it a versatile technique suitable for use on a wide variety of sites.

The method utilises the absorption and reflection of electromagnetic waves at contrasting interfaces. GPR records detailed vertical time sections which can provide a wealth of stratigraphic information and clearly define any discontinuities. The primary advantage of GPR is that it provides a good estimation of the depth of a target. The complex nature of archaeological deposits can present a complicated picture when viewed as individual radargrams. However, data collected along a series of closely spaced parallel traverses can be combined to form a series of time slice maps - horizontal slices through the ground at different time/depth intervals - enabling a 3D image of the survey area. This type of data processing allows more subtle features and relationships between features to be analysed more easily.

Sites Suitable for GPR

• Relatively level and even surface

• Most rural areas, with the exception of saturated peat or clay

• Most urban sites, with the exception of heavily reinforced concrete

• Minimal electromagnetic noise i.e. radio transmitters, certain machinery

Targets Detected by GPR

• Mines and Shafts

• Voids

• Services; pipes, cables, culverts etc

• Foundations

• Ditches

• Bedrock

• Water table