Improvements Continue To Drive GPR Applications

By Jeff Griffin, Senior Editor | April 2009 Vol. 64 No. 4
Mala USA's GPR

GPR data typically is presented as a real time 2D cross sectional image of the subsurface. If multiple cross sections are collected in a grid pattern, the data can be processed and presented as 2D depth slice maps or 3D volumes that can be rotated, sliced and peered into by selectively removing weaker signals to reveal targets associated with stronger signal reflections. Depth slice and 3D images are becoming more widely used because they are generally easier for most people to understand.

GPR provides a "pseudo image" of the subsurface that indicates the position and depth of electrical changes in the subsurface. These changes can be from objects located in the subsurface (i.e. pipes, cables, rebar, rocks, tree roots, foundations) and also changes in the rock or soil structure itself (i.e. soil stratigraphy, fractures, disturbed soil, cavities or sinkholes). It is important to understand that since radio waves have much longer wavelength than visible light waves, GPR images have much less resolution than our eyes see or what a photographic image would provide.

Current GPR systems like the Noggin SmartCart have been made so simple to use that anyone can be quickly trained to use them effectively. Simple GPS integration has made it easy to take GPR data into GIS software and quickly display processed results on Google Earth.

It will be difficult to overcome mother nature on GPR penetration into electrically conductive soils because the transmitter powers required to do so are not practical or legal under the radio frequency emission regulations of most countries. However, the use of GPR will grow from the increased productivity offered by multichannel systems. These systems, coupled with advanced positioning systems, even inside buildings, will soon make real time 2D map and 3D images a reality. (For utility locating, Sensors & Software offers Noggin SmartCart GPR systems and pulseEKKO PRO equipment with a full range of antenna frequencies.)

Vermeer, Keith J. Sjostrom, senior project engineer: GPR systems such as our four wheel cart deployment model are best suited as a utility detection tool within a designated area (intersection, street, construction site, etc) or along a specific bore path or proposed bore or excavation path. Detected targets can be located in real-time quickly and easily and before any excavation commences. Because of the shielded antenna, it can work in areas having EM interference such as overhead power lines, metal buildings and fences, and vehicles. GPR also can be effective in locating multiple targets within congested areas.