GPR Myth Busting: Unveiling the Truths Behind Ground Penetrating Radar in Utility Locating
Ground Penetrating Radar (GPR) is an important tool for locating utilities underground. Reveal’s Field Services team uses MALA single and dual frequency pushcart 2D GPRs, and Kontur multi-channel vehicle mounted GPR arrays to locate utilities, each of which have their own value in different locating environments.
Pushcart 2D GPRs allow our utility locators to survey sidewalks and tighter areas of urban centers on foot, while the multichannel GPR is vehicle mounted and enables the team to capture large sections of road corridors quickly.
However, like any specialized tool, GPR has its limitations and there are many myths about how GPR performs. In this article, we aim to debunk some common myths surrounding GPR and shed light on its true capabilities and applications in utility locating.
The MALA GPR unit locates utilities through a range of different soil types, from urban centers to rural locations.
How Does GPR Work?
Ground Penetrating Radar (GPR) necessitates two primary components: a transmitter and a receiving antenna. The transmitter emits electromagnetic energy into the soil and other materials. The functioning of GPR involves transmitting a pulse into the ground and capturing the reflections produced by subsurface objects.
When the electromagnetic pulse encounters an object, the object's density influences the reflection, refraction, and scattering of the signal. The receiver picks up the returning signals and registers variations within them. The system incorporates software that interprets these signals, generating images, in the form of sets of hyperbolas, signaling the presence of subsurface objects. GPR is a useful tool in utility detection and mapping but is primarily a geophysical instrument that requires expertise to effectively interpret collected data.
Myth 1: GPR Can Find Everything
One of the prevailing myths about GPR is that it possesses magical powers to find all underground utilities, so no other techniques are required. While in theory GPR reflection will occur from any feature with enough dielectric permittivity contrast to the surrounding soil, in practice not all utilities will be seen. Limiting factors include:
Soil conditions: high conductivity soils limit the effectiveness of the GPR reflections in detecting penetration depth.
The contrast between a target, such as an underground utility, and the surrounding soil may be low, and the resulting weak reflections are either not strong enough to be detected, or may be obscured by background noise.
The size of a target is smaller than the resolution limit of the selected GPR frequency, or a target is deeper than the range of the selected GPR frequency.
A target is obscured by another feature; GPR in most scenarios, will not detect a subsurface utility directly below another utility, and multiple utilities laid in a common trench may only give a single GPR response.
Other features such as buried rocks etc., can be difficult to differentiate from utilities in some cases, and in some cases, these features may obscure reflections from the desired targets, like subsurface utilities.
It is essential to understand the characteristics of the site being scanned, its soil types, and the utilities being searched for, to ensure there is a realistic expectation of GPR's performance.
Myth 2: GPR Can Replace All Other Utility Locating Methods
GPR is not a one-size-fits-all solution. Different utility locating methods complement each other, and a best practice approach involves using GPR in conjunction with electromagnetic locators (EML), as well as conducting site feature inspections and manhole investigations. This is in addition to analyzing available as-builts to create a plausible case of evidence for utility locations. Each surveying technique has its strengths and weaknesses, and combining them enhances the accuracy and reliability of a survey.
Myth 3: GPR Can Tell You What A Utility Is
GPR can show you that a utility may be present, but it cannot directly determine what type of utility. GPR reflections are caused by a contrast in dielectric permittivity (essentially, the ability of a material to be a capacitor) between a target, like a utility, and the ground. In a typical GPR utility survey, the user is not able to accurately determine the dielectric permittivity of the ground, which may vary considerably both horizontally and vertically across an investigation site.
Myth 4: GPR Is Foolproof And Requires No Expertise
While GPR technology has become more user-friendly, proper training and expertise are still crucial for obtaining accurate and meaningful results. Interpreting GPR data correctly requires a deep understanding of the technology, the targets in question ( i.e. utility networks), subsurface conditions, and potential sources of interference. Misinterpretation of GPR data can lead to costly project overruns and potential utility strikes further into projects. It is important to invest in training or employ qualified utility locators to maximize the benefits of GPR in utility locating.
Myth 5: GPR Works Equally Well in All Environments
The effectiveness of GPR can be influenced by the environmental conditions. Factors such as soil type, moisture content, and the presence of other materials can impact the performance of GPR. Utility dense, congested environments like in a city center or power substation, can lead to GPR data that is difficult to interpret due to the overlapping nature of GPR reflections within a concentrated network area. GPR users should be aware of the specific challenges posed by different environments to optimize data collection and interpretation.
Conclusion: Separating Fact from Fiction
Ground Penetrating Radar is a valuable tool for utility locating, providing non-invasive insights into the subsurface. However, it is crucial to dispel myths and misconceptions surrounding GPR to harness its full potential responsibly. By understanding its limitations and strengths, utility locators can make informed decisions, ensuring more accurate and reliable data collection.
If you are having trouble interpreting your data, reach out to Reveal hello@reveal.nz. Our expert team can help.