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Ground Penetrating Radar Survey (GPR)

The GPR method provides high vertical and horizontal resolution data that can be quickly acquired while towing the instrumentation behind a vehicle or pulled along the ground while walking. Data are normally acquired at high resolution time or distance intervals, allowing compilation of continuous depth profiles along survey lines.

A GPR transmitter antenna emits electromagnetic waves into the ground which are partially reflected at subsurface interfaces and detected by a receiver antenna. Reflections result from contrasts in the dielectric constant of subsurface materials and stratigraphic layering. Given an estimate of radar velocity, corresponding reflector depths may be determined. Depth analysis can be further enhanced by intrusive methods, such as test pits and bore holes.

Maximum GPR penetration depth is mostly controlled by antenna frequency and the electrical conductivity of subsurface materials; GPR depth penetration decreases with an increase in antenna frequency and/or ground conductivity. Increased ground conductivity resulting from clay-rich soils and/or dissolved salts can significantly reduce the effective range of GPR signals to sub-metre depths.

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