GPR (GROUND PENETRATING RADAR)
METHOD
GPR systems use a pulsed electromagnetic (radio wave) transmitted via a tuned frequency antenna that can penetrate soils, rock, concrete, and many other natural and man-made materials. Reflection events from geological or hydrological boundaries, between sufficiently contrasting materials, are recorded by a receiver antenna. GPR energy pulse is reflected back to the antenna. Energy also keeps traveling through the material until it either dissipates (attenuates) or the GPR control unit has closed its time window. The rate of signal attenuation varies widely and is dependent on the properties of the material through which the pulse is passing. A time-depth cross-section (radargram) of the shallow subsurface is constructed as the radar system is moved along a survey line. The radargram can be depth calibrated to enable detailed interpretations knowing the investigated materials.
PROCEDURE
GPR equipment can be run with a variety of power supplies ranging from small rechargeable batteries to vehicle batteries and normal 110/220-volt. Data is collected in parallel transects and then placed together in the appropriate locations for computer processing in a specialized software program. The computer then produces an horizontal surface at a particular depth in the record. This is referred to as a depth slice, which allows operators to interpret a planview of the survey area. In many situations, a GPR operator will simply note the location of a target so that it can be avoided. For these clients, it may only be necessary to use a simple linescan format in order to mark the approximate area of the target on the survey surface. Other clients may require detailed subsurface maps and depth to features. These situations will require the operator to use mathematical functions to the data in order to remove background interference, migrate hyperbolas, calculate accurate depth and much more.
APPLICATIONS
- Archaeology
- Utility mapping
- Structure inspection
- Sedimentary cover
- Geological structures
- Cavity detection
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