Ground Penetrating Radar¶
Ground penetrating radar (GPR) is an electromagnetic method used for very near surface applications; metres through 10s of metres. It is sometimes referred to as echo-sounding. GPR exploits contrasts in electromagnetic properties (dielectric permittivity, electrical conductivity and magnetic permeability) in order to define the physical boundaries of shallow structures (both natural and man-made). GPR is ideal for near-surface applications because it provides higher resolution images than methods such as FDEM, TDEM and magnetotellurics. GPR surveys are generally performed on a small scale. Depending on the application, various transmitter-receiver configurations can be used. GPR systems can also be mounted to helicopters or placed in boreholes.
GPR has been used successfully to:
- Investigate concrete structures and roads
- Map the layered structures of peat-bogs, sedimentary sequences and glacial environments
- Obtain the depth to groundwater or permafrost
- Locate buried infrastructure such as irrigation pipes, tunnels and electrical wires
- Find unexploded ordnance
The basic conceptual understanding of GPR is shown in Fig. 219. During GPR surveys, a source antenna (Tx) is used to send a pulse of radiowaves (10 MHz to 2.6 GHz) into the ground. As the radiowaves propagate through the Earth, they are distorted as a result of the Earth’s electromagnetic properties. At boundaries where the subsurface electromagnetic properties change abruptly, radiowave signals undergo transmission, reflection and/or refraction. Sensors (Rx) measure the amplitudes and travel times of radiowave signals that have been distorted by the Earth. This information is then used to image discrete targets and physical boundaries.
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