What is Ground Penetrating Radar (GPR)?

 In a nutshell, it’s a technology that allows us to detect and map underground   utilities and assets safely, without excavation.  This is why it is referred to as   non-destructive/non-invasive subsurface imaging.

 GPR is one of the most versatile and effective non-destructive technologies   available for subsurface investigations. Using high frequency radar pulses, GPR   creates images of the subsurface that help detect hidden objects, changes in   material, voids, and structural components across a wide range of environments.   These insights are critical for preventing utility strikes and knowing what lies   beneath before you even break the soil.

What are the limitations of GPR?  Is it right for my job site?

The short answer is, it depends.  GPR suitability is contingent on many different attributes from the size and scope of what you are trying to identify, to it’s material properties, and even down to the characteristics of the soil.

For instance, if the target you are trying to find is very small, and very deep, it is unlikely to be identified by any GPR unit, no matter how powerful or advanced.  On the other hand, large and shallow objects are generally very easy to identify.  A general rule of thumb is “1 in 24”.  Meaning that a 1” pipe is typically visible in the top 24” of soil.  A 2” pipe is visible in the top 48” of soil.  And a 3” pipe is able to be located in the top 72” of soil.

A Deeper Dive into GPR

  • The material properties of the target we are looking for are also very important in the likelihood of finding the target.  GPR essentially measures and displays differences in interfaces between dissimilar materials.  It does this by sending out an electromagnetic pulse and measuring the amount of time it takes for the pulse to return to the GPR unit.  We use something called a “dielectric constant” (K) to determine how likely a target will be to see in the substratum in which it is buried. 
  • The dielectric constant measures how much the electromagnetic wave slows down in a particular material.  For instance, in air the GPR pulse travels at 0.3 m/ns.  In water it travels at 0.033 m/ns, about 10x’s slower, thus giving us very different dielectric constants for each material.  While we don’t usually scan air looking for water, the principle translates over to allowing us to estimate the likelihood of finding a target.  If we have a 1” PVC pipe full of water (0.033 m/ns, K=81) buried in dry sand (0.15 m/ns, K~3-6) at a depth of 18” it is highly likely we can find it since it meets all our requirements for GPR use.  That being size of target and differences between material composition. 
  • If we took that same pipe, removed the water and filled it with air, it would be much harder to find since the dielectric constant of PVC is about 4, right in the middle of the 3-6 range of dry sand.  While locating the pipe isn’t impossible, it is more challenging and cannot be guaranteed. 
  • While there isn’t a way to get around the physics of this situation, we use the latest technology with advanced software processing and unique transmit/receive wave dynamics to produce a very high resolution image that gives us the best chance of locating even the hard to find underground objects.

A Great Example...

of how advanced GPR technology can find objects that were previously un-locatable is this screenshot of a scan of a fiber-optic cable buried in dry soil in an area of high RF interference.  The dielectric constant of the soil and target are very close, and we only see a very slight response in the GPR scan.  We were able to identify and trace this line in our post-processing software, it was barely visible when actually on site. 

Another example of a GPR scan...

where there was actually a large difference between the dielectric properties of the soil and the target.  Here we were tasked with identifying a septic line under a concrete slab.  You can see the metal reinforcement very clearly (blue tags), along with a large disturbance from the sewage line, a 3” PVC pipe buried about 18” deep under the slab, in clay, in a trench full of gravel (green tag).



What is Electro-Magnetic Locating (EM)?

  • EM locating involves directly connecting to, or inducing a signal on, a metallic facility or object and sending a signal down the conductor with a transmitter that we can then trace with an EM receiver.
  • An EM locator is a precision tool that detects electromagnetic signals from buried metallic pipes and cables, allowing our technicians to mark their horizontal location and depth.
  • EM locating is highly accurate when properly implemented by trained technicians and is less susceptible to soil conditions and RF interference than GPR.
  • EM locating is often paired with GPR to provide complete coverage, as EM cannot reliably detect non-metallic utilities like PEX, PVC, or fiber optic lines.
  • Since EM locating is reliant upon conductive utilities, gas lines and fiber optic lines will often have a metallic “tracer wire” buried alongside it to facilitate in tracing the lines in proposed excavation sites.  When the wire is intact, it serves as a quick and easy way to trace the utility.  However, sometimes the tracer wires break or corrode, vastly reducing the ability to induce a signal on it, and necessitating other methods (like GPR) to mark it’s location.

What is GPS/GNSS/RTK?

  • GPS stands for Global Positioning System, which is a satellite-based navigation system that provides location, velocity, and time information to a GPS receiver anywhere on or near the Earth. It operates independently of any telephone or internet reception and is widely used in various applications, including navigation for vehicles and smartphones.


  • GNSS stands for Global Navigation Satellite System, which refers to any satellite constellation that provides global positioning, navigation, and timing services. Examples include GPS (USA), GLONASS (Russia), Galileo (EU), and BeiDou (China).


  • RTK is a GNSS correction technique that uses a network of permanent reference stations instead of a single local base station to deliver inch-level positioning accuracy over broad regions. It replaces the need for users to install and maintain their own RTK base station, enabling high-precision navigation without on-site hardware.
  • All of our locating equipment is capable of logging precise location data, down to a few inches, of any underground utilities or targets/anomalies detected from our scans. 
  • We can use this data to create precision reports documenting everything we find subsurface so that when the marks on the ground have faded, you’ll still have the ability to find what you’re looking for at your fingertips.