Ground Penetrating Radar:

Ground Penetrating Radar (GPR) entered the buried utility locating scene more than a decade ago. Like all new technology, GPR was quickly promoted as the next great solution for utility locating.

GPR has followed the usual trajectory of a new technique in that expectations were inflated and many practical problems overlooked. As the rosy scenarios faded and reality set in, adoption of GPR slowed and the method was strongly denigrated by some as useless. We are now seeing the return of balance with increasing use of GPR for utility locating. Several factors are responsible for this positive outcome.

Complex Locates

The complexity of locating buried utilities continues to increase with time. In the early days of locating, the primary drivers were safety and the cost of repair. The most important buried utilities were usually gas and electricity simply because they were both a safety concern and also most widely distributed.

The standard tools for locating buried pipes and cables depended on detecting electric currents flowing in the utility metallic structure or in an associated tracer wire. The initial EM (electromagnetic) sensing technology was relatively simple. EM locating instruments have evolved greatly over time incorporating multiple field sensors, a wide range of operating frequencies and both active and passive sensing to address ever more complex situations.

Today, the cost of collateral damage and collateral safety concerns are much higher. The loss of communications, water supplies or sewers in urban areas now represents a major cost and safety concern. In addition, there are now more targets located in congested areas, which create even bigger challenges for locating.

Overall, the complexity of locates has increased considerably. Regulations requiring buried utility identification and location marking before excavation now force a standard of performance on buried asset owners to provide validated site clearing. Many jurisdictions have made a one-call process mandatory, require in-field plant location validation to be made by a direct detection method and impose strict time limits on result delivery.

Advanced locating service in some areas triage locates into three types: First, if records indicate no plant then an immediate ‘office’ clear can be made. Second, if plant is in the area, then a standard EM locate is normally carried out. Third, if the traditional approach fails, then the locate is deemed complex and more sophisticated tools such as GPR and even vacuum excavation to expose plant are employed.

Skills Development

In the early days of utility locating, the locating tools were relatively simple to operate. Further, in-field locators were often limited to finding a single type of utility. Now locators are often required to locate more than one type of utility at a site. Locating several utilities with differing attributes requires changing locating procedure and instrument parameters to achieve optimal results. This calls for more advanced instrumentation and higher skill levels in locating technicians.

Professional locators now need a host of skills and must continue to learn and adapt. First, the locators must be able to plan efficient field operation, requiring the ability to examine maps and extract information from database records. Critical skills are computer literacy plus CAD GIS drawing database manipulation. Also essential is a solid knowledge of construction practice for a variety of utilities. Skills in operation of multiple types of locating instrumentation are mandatory. Further, the optimal way to couple energy into the target and the ability to identify the correct responses all demand in-field technical adaptability and acumen.
All of these changes mean that the locating technician of today is a very skilled individual with much more knowledge and the ability to use complex technology.

GPR Technology

Early GPR technology was relatively primitive and the data presentation complex. Further, GPR is extremely sensitive to soil conditions and soil clutter making the analysis of the GPR data difficult for the uninitiated.
Over time, GPR technology has changed little in terms of sensitivity but enormous changes have occurred in terms of its functional form and information presentation. Continuous adaption to make the data much more practical and presentable in real-time enables operators to make real-time decisions on location, depth and other target attributes. Systems have become lighter and more portable and self-contained. Further, soil complexity is better understood and the knowledge base of GPR limitations is much increased.

The skills increase of locating technicians makes GPR much more viable. GPR needs computer image display for effective data evaluation. Computer savvy operators are now becoming highly skilled in using GPR effectively. In some jurisdictions, GPR is a standard addition to the conventional EM current locating instruments. Generally speaking, GPR comes into its own for complex locates where either non-metallic targets are present or a high density of buried features make conventional EM tools ineffective.

GPR technology is now evolving to allow 3D imaging onsite. While developments in this area are still ongoing, progress is rapid. Further, the ability to integrate GPR data with other information from other sensors plus integrating information from historical records right in the field is further advancing the utility of GPR.

Looking ahead, there will be continuing adoption of GPR. Locating crews addressing complex locates will require a variety of tools at their disposal. From the simple locate and mark for excavation to the growing area of subsurface utility engineering (SUE) mapping, GPR is seeing ever increasing use and demands. Continuing technology improvement will see GPR advance further in the coming years.

Greg Johnston is an applications geophysicist for Sensors and Software.
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