How Ground Penetrating Radar Works To Find Underground Utilities 


Ground Penetrating Radar (GPR) is a non-destructive geophysical method used to detect subsurface objects and structures buried below the ground, such as pipes and cables.

It has become an essential tool for industries such as construction, utilities, archaeology, and in locating underground utilities, archaeological artefacts, and geological formations. 

This article will discuss how GPR works to find underground utilities.

How GPR Works

Ground Penetrating Radar works by emitting electromagnetic waves into the ground through an antenna and receiving the reflected waves that bounce back from subsurface features and structures. 

The waves are triggered by an encoder wheel that rotates and sends a signal for the antenna to fire a wave of electromagnetic energy at set frequencies and wavelengths. 

The waves are transmitted and pulsed through the ground until they encounter a boundary between materials with differing electrical properties. 

How GPR works in finding Underground Utilities service provided by Geoscope
How GPR works

When this happens, the waves are reflected off the object or layer, creating an echo effect that can be interpreted by the user as a difference within the subsurface. Much like the objects and different materials underground such as pipes and cables.

The speed and strength of the GPR waves will return to the receiving antenna at varying rates depending on:

  • The ground soil type
  • The utility material type
  • The difference between dielectric constant properties of the ground material and the utility material 

If you are interested in learning more about how GPR equipment works, here’s an article for you! 

Ground Penetrating Radar – A GPR Expert’s Guide

GPR is used in many different geotechnical investigations but works well and is commonly used for finding underground services and utilities.

GPR Information

The main components of GPR equipment

A GPR system consists of a control unit, antenna, power supply, data storage, positioning system, and display. 

The control unit sends signals to the antenna to emit electromagnetic waves and receive the reflected waves. 

The data is then stored and displayed on a monitor for analysis.

Definition of Main Components

Control Unit

This is the main processing unit that controls the GPR system and displays the results.

Control Unit component of GPR


This is the device that transmits and receives electromagnetic waves. It is typically a specialised type of antenna designed for GPR applications.

Antenna component of GPR

Power Supply

This provides power to the GPR system, which can be battery-operated or powered by an external source.

Power Supply component of GPR

Data Storage

This is used to store the raw data collected by the GPR system.

Positioning System

This is used to determine the location of the GPR system and map the data collected to a specific location. This can be achieved using GPS or other positioning technologies.


This displays the data collected by the GPR system in a form that can be interpreted by the user. This can be a screen or other visual display, or a printout or digital file.

Display Monitor component of GPR

Electromagnetic Radiation

Electromagnetic radiation refers to the energy that travels through space in the form of electromagnetic waves. 

It includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

 Electromagnetic radiation is present in everyday life and can be harmful in high doses.

3D rendering of Electromagnetic Radiation
3D rendering of Electromagnetic Radiation

Electromagnetic Waves

Ground Penetrating Radar uses electromagnetic waves in the radio wave portion of the electromagnetic spectrum. These waves are sent into the ground from an antenna and bounce back when they encounter a change in the electrical properties of the subsurface materials.

Ground Penetrating Radar GPR Service Locating Sydney Geoscope
GPR using electromagnetic waves in the raio wave portion

The reflected waves are then analysed to create an image of the subsurface features and structures.

The wavelength and frequency used in GPR antennas determine the depth at which the waves can penetrate the ground

Higher frequencies provide better resolution of shallow features but have limited penetration, while lower frequencies can penetrate deeper but with lower resolution.

In addition to GPR, electromagnetic waves have many applications in our everyday lives. Radio waves are used in communication systems like radios and cell phones, while microwaves are used in microwave ovens. However, there are concerns about the potential harm of electromagnetic radiation, particularly from high-frequency waves such as X-rays and gamma rays.

Applications of GPR

Ground Penetrating Radar has a wide range of applications in construction, engineering, surveying, and geology. Some of the most common applications of GPR are:

Utility Detection

GPR is commonly used to locate underground utilities such as pipes, cables, and conduits. 

By using GPR to locate utilities, construction workers can avoid damaging them while digging, saving time and money.

How GPR works in finding Underground Utilities in Utility Locating Service provided by Geoscope

Concrete Inspection

How GPR works in finding Underground Utilities service provided by Geoscope

GPR can be used to detect voids, delamination, and other defects in concrete structures such as bridges, roads, and buildings. 

This information can help engineers determine the condition of the structure and plan repairs.

Archaeological Investigations

GPR can be used to locate buried artefacts and features, such as walls and foundations, in archaeological sites without the need for excavation. 

This helps archaeologists preserve the site and avoid damaging artefacts.

Portrait of Beautiful Paleontologist Cleaning Tyrannosaurus Dinosaur Skeleton with Brushes. Archeologists Discover Fossil Remains of New Predator Species. Archaeological Excavation Digging Site

Geological Investigations

man geologist examines a mineral sample

GPR can be used to study the subsurface geology of an area.

For example, it can be used to understand the depth and thickness of sediment layers, as well as the presence of faults and other geological structures.

Environmental Investigations

GPR can be used to study the subsurface environment. 

It can be used to detect the location and extent of groundwater contamination and the depth and thickness of soil layers.

GPR being used to detect water lines in Sydney service provided by Geoscope

Detecting Utilities with GPR

To detect utilities with GPR, it is important to approach the target at an ideal angle to obtain a strong hyperbolic response. 

Ground Penetrating Radar being used in a perpendicular angle in Sydney service provided by Geoscope
Ideal angle for GPR

The ideal angle is perpendicular to the utility, by approaching the utility at a 90-degree angle, maximises the amount of energy that is reflected back to the antenna as it will create the strongest reflection. 

If the radar is not run perpendicular to the utility, the energy may bypass the utility and not be reflected back to the antenna, resulting in a weaker hyperbolic response or even a missed signal. 

However, the angle may need to be adjusted depending on the depth and location of the utility.

Factors Affecting GPR Accuracy

Several factors can affect the accuracy of GPR readings, including the type of soil being scanned, the moisture content of the soil, and the presence of other underground utilities or metallic objects. 

In general, dry soils and sandy soils are more conducive to accurate GPR readings, while wet or clay soils can reduce the accuracy of GPR readings. Similarly, underground utilities made of metal or other conductive materials can cause interference with GPR signals, leading to inaccuracies in detecting the depth and location of the utility. 

It is essential to understand these factors and adjust the GPR parameters accordingly to obtain accurate results.

The Limitations of Ground Penetrating Radar

GPR isn’t perfect, and it has its limitations. The following factors can affect its accuracy:

  • The presence of other materials may interfere with the signal.
  • Accessibility of the site survey area.
  • The composition and material of the target utility
  • Ground surface condition.
  • The orientation and depth of the target utility


These can all impact the results of a GPR scan. For example, GPR may struggle to detect utilities in areas with high electromagnetic interference, such as near power lines or electrical equipment.

Additionally, GPR may not be able to penetrate certain types of materials, such as metals or heavily compacted soils, resulting in missed signals or inaccurate readings.

Other Limitations of GPR

Limited Penetration

The depth to which GPR can penetrate the subsurface depends on the frequency and wavelength of the electromagnetic waves used. Higher frequencies provide better resolution of shallow features but have limited penetration, while lower frequencies can penetrate deeper but with lower resolution.

Soil Conditions

Soil moisture content, clay content, and other factors can affect the accuracy of GPR results. In general, dry, sandy soils provide better GPR results than wet, clay soils.


Other subsurface features, such as rocks, tree roots, and metal objects, can interfere with GPR signals and create false positives or negatives. It is important to use multiple detection methods and to interpret GPR results in conjunction with other data sources.


GPR data must be interpreted by a trained professional to identify subsurface features and structures. Misinterpretation of GPR data can lead to errors in construction or engineering projects.

If you want to know more about the limitations of GPR, this article is perfect for you!

Ground Penetrating Radar isn’t perfect – Limitations of GPR

In this article, we will explore the limitations of using GPR for underground utility locations.

The Importance of Using Multiple Detection Methods

It’s important to note that no single method can accurately detect every type of underground utility or object. That’s why it’s essential to use multiple methods when conducting a subsurface investigation.

While GPR is a powerful tool for locating utilities, it has limitations, such as interference from other materials, inaccessible sites, and the depth and orientation of the target utility. 

Other methods, such as electromagnetic locating, can complement GPR and provide a more comprehensive understanding of the subsurface.

Ground Penetrating Radar (GPR) being used together with other utility locating methods service provided by Geoscope
GPR together with other methods

Moreover, visual inspections are crucial for detecting utility markings, surface indicators, and other visible signs of underground utilities. A combination of methods allows for a more accurate and efficient subsurface investigation, minimising the risk of damaging underground utilities during excavation.

Tips or Best Practices for Using GPR in Utility Locating

When using GPR to locate utilities, some tips can help maximise its effectiveness and accuracy. Here are some tips for using GPR in utility locating:

1. Choose the Right Antenna

Choosing the right antenna is crucial for accurate utility locating. Different antennas have different frequencies and characteristics that affect their performance. Ensure that you select an antenna that is suitable for the application and utility depth.

The ideal GPR antenna frequency is somewhere in the middle of the range in frequencies around 450-500MHz. Some GPR has dual antennas to run high and low-frequency antennas simultaneously, ranging around 200-700MHz. 

It depends on the user, although each system has benefits and limitations. 

2. Calibrate the GPR equipment

It is vital to calibrate the GPR equipment correctly before beginning the detection process. This involves adjusting the equipment to the specific soil conditions and utility types in the area. 

Setting the zero level and calibrating the energy velocity through the soil is vital to get accurate depth readings.

3. Keep the Antenna Close to the Ground

When scanning the ground, keep the antenna as close to the surface as possible. This maximises the signal strength and improves the resolution of the image.

4. Take Your Time

Utility locating is a time-consuming process that requires patience and attention to detail. Take your time and scan the area slowly to ensure that you don’t miss any utilities.

5. Cross-Check with Other Methods

Cross-checking with other methods such as electromagnetic locating and visual inspections can help confirm the accuracy of the GPR results.

Ground Penetrating Radar (GPR) is a powerful geophysical technique that uses electromagnetic waves to detect subsurface features and structures. 

GPR has a wide range of applications in construction, engineering, surveying, and geology, but it has limitations that must be understood to ensure a thorough investigation. 

By understanding how GPR works, its applications, and its limitations, professionals in these fields can make informed decisions about when and how to use GPR to obtain accurate and useful information about the subsurface environment.

If you are looking to avail GPR Services, we highly recommend the most trusted and reliable GPR Service provider — Geoscope

Expert Ground Penetrating Radar Services

Sydney’s Best GPR Services, Guaranteed!
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Patricia Cupiado

Co-Author of this Article

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