Frequency domain
GPR — Ground Penetrating Radar
High-frequency radio pulses for centimetre-scale shallow imaging
Frequency band
10 MHz - 2.6 GHz
Depth range
0.1 - 30 m
Resolution
Very high (centimetres)
Source
Impulse radar antenna
Typical cost
Low
Survey speed
Fast - walking or vehicle towed
Best terrain
Dry, resistive ground; concrete; ice; sand
Domain
Frequency domain
Overview
A short radio pulse is radiated into the ground and the reflections from dielectric contrasts are timed. It is the only geophysical method routinely delivering centimetre resolution, but conductive clay and saline ground absorb the signal quickly.
How the physics works
Pulse velocity is set by the relative permittivity, v = c / sqrt(er). Reflections occur wherever permittivity changes. Attenuation scales with conductivity, so the depth-versus-resolution trade-off is decided by the antenna centre frequency and the ground itself.
Where it is used
- Utility detection and concrete scanning
- Archaeological and forensic surveys
- Pavement, bridge deck and tunnel lining inspection
- Glaciology, permafrost and shallow stratigraphy