GPR Explained

Ground Penetrating Radar, also known as GPR, is the cornerstone of the origin story of GPRS. We wouldn't be here today if Matt Aston hadn’t discovered a GPR unit in an ad in the back of a magazine. 

Over the past two decades GPRS has expanded to add video pipe inspection, leak detection, 3D laser scanning, drone imaging, and mapping & modeling to the list of services we provide. Yet GPR has continued to play a key role in allowing us to help clients Intelligently Visualize the Built World™.

GPR’s ability to scan concrete for subsurface anomalies is different than the technology used for concrete structural analysis. For specific structural analysis testing, GPRS uses GPR in tandem with Ultrasonic Pulse Velocity (UPV) testing and imaging, tomography, drone photogrammetry, and even 3D laser scanning services to completely assess concrete structures.

GPR as a technology continues to improve by leaps and bounds. Combined with the knowledge and skill of our elite Project Managers, it can produce results that are clearer and more accurate than ever before.

What is Ground Penetrating Radar?
Ground penetrating radar (GPR) is a non-destructive detection and imaging method which identifies subsurface elements either underground or within a surface such as concrete.
According to the New York State Museum, GPR was invented in the 1930s as a tool for measuring the thickness of glaciers. It wasn’t until the mid-1980s that the technology advanced to a stage where it became affordable for widespread use.
GPR can detect both metallic and non-metallic objects, giving it a wide range of applications. It reveals all types of utilities, including electrical conduit, steam pipes, telecommunications lines, gas & oil lines, water lines, and sewer & storm pipes. GPR can locate the presence of voids, rebar, conduit, post tension cables, and other structural elements hidden within concrete.

How Does Ground Penetrating Radar Work?
In short, GPR works by sending a radio signal into a structure and reading the “bounce.” The radio wave bounces off any material it encounters and creates a reading that displays those bounces as parabolas. An experienced GPR technician interprets this reading to determine the type of material located.  GPR is extremely accurate. However, external factors such as ground and soil conditions, proper use of equipment, and correct interpretation of readings can affect accuracy. In cases where GPR may not be the appropriate tool for the job, GPRS will use complimentary underground imaging technology such as electromagnetic (EM) locating to identify subsurface obstructions. 

What is GPR Used For, and Why?
‍As stated above, the uses for ground penetrating radar are many and varied. 
GPRS uses GPR to map underground utilities and other findings, and to scan for materials in concrete. We do this to help our clients avoid the costly and dangerous repercussions of striking any of these subsurface objects during construction activities. Scanning and locating services enable contractors or homeowners to get a clear picture of what lies beneath before continuing with a project. 

Can GPR Determine the Exact Size of a Subsurface Void? 
No. GPR equipment can identify the area where a void is occurring and the boundaries of that void. It cannot measure the void's depth.

Can GPR Scan Concrete Masonry Unit (CMU) Walls? 
Yes, GPR can determine the presence of grout and vertical rebar within the CMU structure.‍

Does GPR Work on Vertical Surfaces or Ceilings? 
Yes, GPR can scan for the location of rebar in concrete columns and walls. It can also scan the underside of a floor to mark out the reinforced steel and any embedded conduits. 

Can GPR Locate Unmarked Graves? 
Yes, GPR can determine the location of unmarked graves for site planning purposes. Older grave sites can be harder to locate because of material deterioration. In most cases, however, the grave sites can be accurately marked out. 
It’s not just unmarked graves. GPR professional services are sometimes utilized on popular television shows that focus on the search for ancient artifacts and other historically valuable objects. GPRS has assisted with some of these investigations in the past, including appearing on the CW’s Mysteries Decoded series to investigate a Rhode Island home predating the American Revolution. 
GPRS recently scanned the cornerstone of a 175-year-old church in Pennsylvania which, according to historical records, conceals a time capsule containing a treasure trove of religious documents. ‍

How Deep Can GPR Penetrate? 
The depth of GPR depends on the application. For concrete scanning, the radar used can penetrate depths of 18-24”. For private utility locating needs on grass, soil, asphalt, or concrete, the type of antenna used can penetrate up to 8’. 

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Does GPR Have Any Limitations? 
Yes. Ground and soil conditions, weather, and type of material located are a few of the potential limiting factors. An experienced GPR technician will be able to assess your site’s condition to determine if GPR is the proper tool for the job. 

Is GPR Safe to Use? 
Yes. GPR is a safe, non-invasive, non-destructive tool. It does not emit any harmful radiation or other byproducts, and it does not create any noise. The scanned area remains undisturbed. 
GPR has replaced x-ray technology as the first choice for precision concrete scanning. GPR is non-destructive like x-ray, and it has the added benefit of emitting no harmful radiation. Plus, it can quickly scan large areas with no prior set-up necessary. 

How Can I Determine if GPR is Needed for My Project? 
GPR is commonly used to scan and identify subsurface elements. It’s always wise to conduct a GPR scan before beginning any renovation or demolition activities. This typically includes any excavation work deeper than 18”, or any coring, cutting, or drilling of concrete. 
The best way to know whether you need GPR is to contact an experienced GPR technician to evaluate your project and its needs. GPRS’ elite Project Managers not only know how to use GPR to Intelligently Visualize The Built World™, they also know when it isn’t the best tool for the job and they need to use a different technology to help you keep your people safe, and your project on time and on budget.
With over 400 GPRS Project Managers stationed in every major market across the United States, you can be sure that there are quality GPR scanning services near you. GPRS provides a host of infrastructure visualization services to help you locate and evaluate your utilities and other subsurface structures. 

What can we help you visualize?