Ground Penetrating Radar

Ground penetrating radar uses pulses of electromagnetic energy to survey the subsurface. When the EM pulse hits an object (such as a utility, a buried pipe or a change in stratigraphy), the density of the object causes it to reflect, refract, and scatter the signal. The return of the reflected signal is recorded by the system and used to identify objects and to determine their depth. The resulting data is plotted as profiles or planview maps isolating specific depths or in three-dimensional models. Ground penetrating radar is a non-intrusive and non-destructive survey technique that can be used in many different applications including utility location, void detection and pipe inspection.

An Introduction to Ground Penetrating Radar (GPR)

Voids are detected by the presence of two peaks on the GPR data, one at the interface between soil and air and the other at the surface of the void. The void dimensions can be estimated from the time difference between these peaks. GPR is also effective in detecting changes in material composition, such as the change between solid and void.

The accuracy of GPR measurements is dependent on how precisely the travel time is related to actual depth units. This is influenced by the choice of antenna frequency, which provides a trade-off between penetration depth and resolution; by equipment positioning differences; and by the site-specific conditions. A good understanding of the geological setting is therefore important when using GPR for surveys.

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