In today’s infrastructure and construction environment, non-destructive subsurface investigation is more important than ever. At Centara, we deploy advanced ground-penetrating radar (GPR) systems — including those manufactured by IDS GeoRadar, GSSI, Mala Geoscience and SPX GPR — to tackle a variety of challenging subsurface tasks: from locating sinkholes and mapping land drainage to tracing underground utilities, mapping rebar and structural steelwork, and even identifying suspected un-marked graves.
In this article we explain how GPR works, why such a broad variety of applications is possible, and what the limitations are. We also detail how Centara applies this technology and the practical considerations for each use case
Basic principle
Ground-penetrating radar (GPR) is a geophysical, non-destructive method that uses pulses of high-frequency electromagnetic energy to image subsurface features.
Here’s a simplified step-by-step:
One of the central technical considerations in GPR is antenna frequency. Higher frequencies give better resolution (i.e., finer detail) but shallower penetration; lower frequencies penetrate deeper but with lower resolution. For example, typical maximum penetration depths for concrete or utility surveys may only be a few metres using higher frequencies, whereas in very favourable ground conditions (dry sandy soil, little clay) penetration might reach many metres.
GPR works because of contrasts in electromagnetic properties. A buried object (metal pipe, rebar, void, disturbed soil) will often have a significantly different dielectric permittivity or conductivity than the undisturbed surrounding medium. That contrast produces a reflection.
Here is how Centara uses GPR in six key application areas: sinkholes, underground utilities, rebar/concrete scanning, land drainage, and un-marked graves.
Sinkholes and subsurface voids (for example beneath pavements, floors, or in land areas) pose serious safety and structural risks. At Centara we deploy GPR to identify areas of anomalous subsurface conditions (voids, cavities, disturbed material, anomalous layering) that may indicate a developing sinkhole or collapse risk.
Because GPR can detect changes in layering and reflectors (for example a void will show up as a strong reflector or disrupted layering), it can provide early warning of voids before collapse. In favourable ground conditions, this is a cost-effective, non-destructive method.
Locating underground utilities is a major use-case. Many utilities are non-metallic (plastic ducts, fibre-optic conduits, concrete sewers) and cannot always be detected by traditional electromagnetic utility locators. GPR is ideal because it detects all objects that produce a dielectric contrast (metallic or non-metallic).
At Centara we can survey an area (soil, asphalt, concrete) scanning in grid patterns, record the radar-gram data, identify the utilities’ location, depth and orientation, and produce a map/plan for the client. The use of multiple antenna frequencies (via our IDS, GSSI, Mala, SPX systems) allows us to tailor resolution vs penetration depending on expected depth and ground conditions.
In building refurbishments, floor cutting or drilling through slabs, knowing where rebar, post-tension cables, conduits and voids are is vital. GPR excels here. For example, high-frequency antennas (such as 1.5 GHz or 2.6 GHz) can provide high resolution and map rebar mats at shallow depths quite accurately.
Centara uses GPR to scan concrete floors, walls and ceilings to map reinforcement, locate embedded conduits or utilities, and identify potential hazards prior to coring or cutting. The non-destructive, non-intrusive nature of GPR means minimal disruption.
Land-scaping, sports fields, golf courses, infrastructure corridors often have drainage features (pipes, infiltration layers, gravel drainage channels) that may be undocumented or changed over time. Centara uses GPR to detect drainage pipes, voided drainage layers, and the condition of subsurface drainage systems.
Because the contrast between filled/unfilled drainage channels and surrounding material is detectable, our surveys help clients map existing drainage networks, assess condition, identify blockages or collapse risk, and plan rehabilitation.
One of the more sensitive applications is locating un-marked graves. In forensic, archaeological or heritage-contexts, GPR can identify anomalies consistent with burial features (e.g., disturbed soil, voids, coffin remains, layering changes) without excavation.
At Centara we approach these surveys with great care, appropriate data collection parameters (often lower frequency for greater depth, grid scanning, careful processing) and collaborate with heritage/archaeological specialists as required. The ability of our GPR systems (IDS, GSSI, Mala, SPX) to produce high-resolution imaging aids in providing credible mapping for planning and documentation.
Centara also applies ground-penetrating radar to investigate masonry arch bridges, where the position and condition of hidden structural steelwork such as tie-bars, reinforcement beams, or embedded strengthening plates must be determined without destructive testing. Using mid- to high-frequency GPR antennas, our surveyors can detect the characteristic reflections produced by ferrous metal within stone or brick masonry.
By scanning along and across the bridge span, we generate detailed radar-grams that reveal the depth, alignment, and continuity of the steelwork. This information supports engineers in assessing load-carrying capacity, verifying as-built details, planning refurbishments, and identifying areas where corrosion or voiding may have compromised the structure. The non-intrusive nature of GPR makes it particularly well suited for historic bridges, allowing condition assessment and preservation planning while maintaining structural integrity.
To summarise:
While GPR is a powerful tool, it is subject to limitations and practical constraints. Centara always assesses these before deployment to ensure relevance and manage expectations.
Ground/Material conditions
Depth vs resolution trade-off
As discussed: higher frequencies = finer detail but shallow penetration; lower frequencies = greater depth but lower resolution. For example, rebar mapping might use 1–2 GHz (shallow), whereas a deep utility survey might use 200–400 MHz (deeper but less detail).
Interpretation ambiguity
GPR data is not always straightforward. A reflection may indicate a void, a pipe, a rock, or simply a change in soil layering. Without calibration (known reference), the depth, size and nature of the anomaly may remain uncertain.
Calibration and survey design
For accurate depth estimation you often need to know wave velocity in the medium (which may vary). Incorrect assumptions can lead to depth errors. Also survey density, grid spacing, antenna coupling, operator skill all matter.
Practical onsite constraints
Specific to un-marked graves & heritage surveys
By leveraging advanced ground-penetrating radar systems from IDS, GSSI, Mala and SPX, Centara is able to provide high-quality non-destructive subsurface investigations across a wide range of application areas: sinkholes and voids, underground utilities, concrete/rebar scanning, land drainage, and heritage/forensic un-marked graves.
While GPR is an extremely powerful technology, its success depends on correct antenna selection, survey design, ground conditions, and careful interpretation. Centara’s expertise ensures that clients receive actionable subsurface intelligence, with risk and ambiguity clearly managed.
To discuss the requirements for any GPR projects please contact us – 01924 220726 or email info@centara-ltd.com