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GPR Concepts
5 GPR Concepts
5.1 Theory
Ground penetrating radar (GPR) technology uses radio waves to image objects in the
subsurface. The subsurface may consist of soil, rock, asphalt and other materials. GPR
systems emit high frequency radio wave pulses and detect the echoes that return from objects
within the subsurface. Echoes are produced when the target material is different from the host
material (e.g. PVC pipe in gravel)
5.2 Hyperbolas
The GPR display shows signal amplitude versus depth (time) and sensor position along a line.
This is called a "Line Scan". Since radar energy radiates in a 3D cone shape rather than a thin
beam, a hyperbola (or inverted U) is the GPR response from a small point target like a pipe, rock,
or a tree root. The radar wave hits the object before and after going over it and forms a hyperbolic
reflection that can appear on the record even though the object is not directly below the radar:
Hyperbolas are best viewed when subsurface targets are crossed perpendicularly (at a 90
degree angle). The actual position of the object is located at the apex of the hyperbola.
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