Ground probing radar or ground penetrating radar (GPR) is a high resolution, field-portable geophysical method that produces graphic sections of subsurface structure. Typical site investigation applications of ground radar include the accurate location of voids and buried obstructions; mapping subsurface soil and rock interfaces and defining buried archaeological structures. The ground radar method is also able to identify ancient landfill sites and detect buried hazardous waste.
Ground radar surveys are non-destructive and non-intrusive, revealing detailed information on subsurface ground conditions without the requirement for drilling or excavation. Results are presented in an easy to understand engineering compatible CAD format.
A typical ground radar system comprises an antenna unit, control console, display monitor and graphic printer. The antenna unit is in direct ground contact, with the remaining equipment either vehicle-mounted or stationary. Data is collected along accurately located profiles, usually set-out in a customised survey grid.
Variable frequency, interchangeable antenna units can be used with the GPR system, depending on the particular application. Low frequency units offer greater depth penetration and are generally better suited for civil engineering and geological site investigations. Small, portable, high frequency units are used for high resolution work involving NDT of concrete and masonry structures (check out GPR for NDT below).
Ground radar works by transmitting impulses of UHF/VHF frequency electromagnetic energy from the moving antenna, which are propagated downwards into the ground. Reflections are generated at any subsurface boundary where an electrical contrast is present. The reflected signals are detected by the antenna receiver and digitally stored by the control console for post-survey processing and interpretation.
Data processing is carried out using specialised interactive software to optimise survey results. Data interpretation procedures correlate reflections on the GPR record with real physical interfaces such as soil or rock layering, voids, foundations and archaeological structures.
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