Ground Penetrating Radar (GPR) systems by ScanMan

Concrete scanning/x-ray or as its better known, Ground Penetrating Radar is a well established non-destructive method of investigating the internal composition of many naturally occurring materials such as rocks, earth and gravels as well as man made materials like brick, concrete and asphalt, etc.

It can be used to detect metallic and non-metallic pipes, conduit, sewers, post tension cables, cables, cable ducts, voids, foundations, reinforcing in concrete and a whole host of other buried objects. It is also used to investigate the depth and make up of different strata layers. A common use has been to scan areas of land before excavation takes place.

Principle of Operation
The radar system sends out pulses of electromagnetic of EM energy and works by detecting the electrical echo caused when the pulse meets electromagnetic discontinuities, such as a pipe or void, within non-metallic structures and materials. By moving the radar across the surface an image is created similar to that of a CT scan.

The measured profile is termed a "time profile." The depth is expressed in terms of Two Way Travel Time (TWTT) rather than true depth. TWTT is the time taken for the signal to leave the antenna transmitter, bounce off the target and the reflected energy to return to the antenna receiver. The longer the time window over which the radar observes the reflected signal, the further the signal will have traveled. Our system has a time window that can be adjusted in steps from 6 nanoseconds (ns) to 800 ns. Generally the operator will be using the equipment in the range of 26 to 50 ns.

A radar wave travels at different rates through different ground materials due to their differing EM Properties. Therefore, in order to be able to plot the profile as a true depth section, some method must be found which enables the speed of the propagation of the radar signal to be determined. If the ground simply consisted of a uniform media with isolated targets buried within it, the depth could be calibrated fairly accurately.

The depth of penetration and the resolution of the measurements depend on a number of factors. Different types of ground behave very differently. Sand, loam, chalk, sand stone, Granite, etc. are all easy to penetrate and the radar can also be used to see through fresh water and snow. Cured concrete and other hard layers can be penetrated depending on the number and spacing of any reinforcing rods present. Soils which have a high percentage of dissolved salts and wet clay are the most difficult to work with.

Surface Penetrating Radar
Surface Penetrating Radar is the use of usually a 1GHz antenna to scan within concrete structures to locate and mark the position of metal reinforcing or conduits. The 1 GHz antenna has such a high resolution picture it can easily pin point something as small as a household telephone wire under 6 to 8 inches of concrete.