The useful question is not “Which technology is better?” It is “What are we trying to find, and what decision does the project need to make?”
Ground penetrating radar and electromagnetic locating investigate underground services in different ways. EM locating follows a signal along a conductive service. GPR records reflections from changes below the surface. On many sites, the best result comes from using both methods and comparing the evidence.
Our locators apply or identify a signal on a conductive pipe, cable or tracer wire, then follow that signal from the surface. Depending on the service and access, they may use a direct connection, a clamp or induction.
EM locating is particularly useful when the service can carry a traceable signal and the operator can follow a logical route. It helps the crew mark the likely alignment and identify where the signal becomes unclear or further investigation is needed.
GPR sends electromagnetic energy into the ground and records reflections from changes below the surface. An experienced operator interprets the responses in the context of the target, surface, ground conditions and survey pattern.
The screen does not show a photograph of the underground service. It shows responses that require interpretation. That is why On Point leads a GPR survey with the project question, not the machine.
| Question | Electromagnetic locating | Ground penetrating radar |
|---|---|---|
| What does it follow? | A signal along a conductive service or tracer wire | Reflections from changes below the surface |
| Where is it strongest? | Traceable conductive services with suitable access and signal | Defined areas where subsurface features may create a readable response |
| What can limit it? | Non-conductive material, broken tracer wire, interference, congestion and access | Ground conditions, moisture, reinforcement, target size, material, depth and access |
| What does it produce? | A traced and marked likely service alignment | Interpreted responses and possible target positions within the survey area |
If the target is a conductive service and the crew can apply or identify a suitable signal, EM locating provides a direct way to follow its likely route. The operator can test the signal, trace the alignment and note where the response changes.
A practical example is a service route that begins at an accessible connection point, passes through a work area and needs to be marked before excavation. The locator can follow the signal while comparing the route with site features and available records.
GPR can add another layer of evidence when the target cannot be traced electromagnetically, the service may be non-conductive or the team needs to investigate a wider area for subsurface features.
On site, the survey conditions can change quickly. A clean run across an open paved area may become more complex near reinforcement, congested services or restricted access. The operator adapts the survey pattern and explains what those changes mean for the interpretation.
One method can test the other. An EM trace may identify the likely route of a conductive service, while GPR adds responses that support or challenge that interpretation. If the evidence still does not answer the critical question, the team can select a point for non-destructive excavation.
That staged approach is more useful than treating every mark or response as equally certain. It shows the project team how the conclusion was reached and where uncertainty remains.
Neither method guarantees that every underground service will be identified. EM locating depends on the service and signal. GPR depends on the target and site conditions. Records can also be incomplete or outdated.
Where physical confirmation is critical, targeted non-destructive excavation may be required. The right scope should match the consequence of getting the decision wrong.
You do not need to diagnose the technology before you call. Troy has built On Point’s locating capability around one practical field question: what information will help the project move forward? That question matters more than choosing a machine from a list.
Tell us what you are trying to find and why it matters. Our team will review the available information and recommend the investigation sequence.
