What is GPR?
GPR stand for Ground-Penetrating Radar which is a survey method that uses an electromagnetic energy signal to image the subsurface. A GPR machine usually comprises of a transmitter, a receiver and a signal encoder. When the emitted energy signal encounters a buried object or a boundary between the materials having different properties, the signal is returned to the receiver and it records a two-way travel time and the strength of the signal. For best results a contrast in electrical properties is needed between the target and host material.
Radar travels at different speeds through different mediums and the more conductive or saturated the medium, the more the signal will attenuate and may limit the effective depth range of GPR investigation.
GPR comes in many different sizes and shapes depending upon the application. High frequency GPRs are for shallow depths and have an improved resolution which is ideal for concrete scanning, whilst lower frequencies are ideal for deeper depths and larger targets such as utility mapping applications.
A few things worth noting with GPR surveys:
- The penetration depth of ‘standard’ GPR for utility mapping is ‘approximately’ 2-3 metres. So it is enough to detect most services underground, however it does have range limitations depending upon the conductivity of the ground nearer the surface.
- The device can’t tell you what the items are – The results are interpreted by the surveyor, not the GPR
- The GPR can’t see through items, so if a large pipe is set directly above two smaller pipes, it is unlikely that the equipment will be able to see them underneath the large pipe
- GPR surveys usually go hand in hand with standard topographic surveys. This gives the utilities survey context and essentially gives spatial meaning to the Utilities Survey. Without the topo aspect of the survey there is nothing to relate the utilities spatial data back to.
One of the main aims of our utilities surveys is to prevent asset strikes when digging on site. Obviously striking assets can be disastrous and extremely dangerous, GPR therefore is used to detect assets, map them out relative to a topographical survey and identify where assets are so they are not accidentally struck during the project, making them safer and cost effective.
For more information you can get in touch with Operations Director, Clif Webb