TECHNOLOGY INSIGHTS
Technology Expertise beyond Ground Penetration Radar
Our experts have answered the questions surrounding GPR for Railways.
At the core of our innovative approach is Ground Penetrating Radar (GPR) technology, seamlessly integrated with our expertise in its application and automation, specifically and only for railways. To understand when, how and what to expect from our GPR inspection and analysis our experts have answered the questions surrounding GPR for Railways.
One very important fact: we do not use algorithms to compare signal amplitudes with reference tables deriving, for example, the Ballast Fouling Index. We are evaluating every radargram individually, focusing on the specific track situation. Of course, we apply software, but have quality gates with human expert reviews and approvals for highest quality results.
Jochen Nowotny, CEO about
Human-Centered Radargram Analysis for Precision
Why should Ground Penetration Radar be used?
GPR detects ballast quality, water accumulation, cavities, cracks or subsidence and explain unusually rapid deterioration of the track geometry. With this, GPR is not a substitute for measuring track geometry but an essential add-on to gain additional information for deriving the correct, most cost-effective maintenance measures.
The following GPR operational procedure is recommended: As first step, the basis for later comparisons must be created. To do this, the entire rail network is measured and evaluated using GPR. This process shall be repeated every three up to maximum of five years.
Whenever now track geometry deteriorates rapidly, GPR is used for this track specific section. With the created reference and over the years available time-series comparison, the most efficient maintenance measure is derived.
The RTA Team helps this process not only by interpreting the radargrams and providing the Key performance indicators, but also by offering a Restructuring advisory service.
What is Ground Penetrating Radar?
GPR utilizes electromagnetic waves to non-invasively explore subsurface structures. The principle is simple: A transmitter emits short pulses of high-frequency radio waves, which penetrate the ground and are reflected at interfaces between different materials. A receiver registers the reflected signals and records the transit time and amplitude. From this data, conclusions can be drawn about the depth, shape and properties of the underground structure.
GPR is used in a variety of fields – from archeology, geology, hydrology, environmental studies, construction and security. A special application is found in the railway system.
In the Railway System Ground Penetration Radar is used for geotechnical track surveying to assess the condition and quality of the trackbed. The trackbed consists of multiple layers forming the proper structure for durable track geometry under the stress of train traffic. These layers can be identified using GPR technology.
What is Ground Penetrating Radar for the Railway System?
Generally, we are looking to determine the following Key performance indicators:
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Ballast Fouling
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Humidity / Permeability
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Clay Fouling / Mud Pumping
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Layer Thickness
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Undulation of the layer boundaries
These parameters are provided in easy-to-read formats and can be displayed in our dedicated RTA.Viewer.
Which Trackbed GPR Key Performance Indicators are determined?
What are the advantages of using Ground Penetrating Radar for Railways?
Compared to alternative methods of geotechnical track surveying like drilling or visual inspection, the advantages are as follows
Non-invasive Testing
GPR causes no damage to the surface or subsurface since it only emits and receives electromagnetic waves
No Track Closures
GPR measurements can be conducted at speeds up to 270 km/h, thereby not interfering with regular train traffic, including High-Speed Railway operations
Rapid Deployment
Inspection equipment can be mounted easily on any rail-bound vehicle in under 90 minutes
Cost Savings
We are not completely replacing drilling, but we support you in saving costs by optimizing where you drill, if at all and we ensure that your maintenance budget is spent optimally.
Are higher Radar Frequencies better?
The short answer is no.
Get ready for some myth busting!
Antenna Frequency
Penetration depth decreases as the frequency of the radar signal increases. Our 400 MHz antenna is uniquely designed for railway applications, offering an optimal balance between penetration depth and ballast size. At frequencies around 2 GHz, while the resolution is high, even individual ballast stones weaken the signal within the first few centimeters. As a result, higher frequencies do not provide better results; in fact, they limit the ability to see deeper layers.
Measurement Depth
The nature of a subsoil, its dielectric properties, determines the speed at which the radar signal can propagate, how strongly it is attenuated, reflected and refracted. Every change in the subsoil material results in a change in the dielectric properties, whereby parts of the radar signal are reflected and thus become visible in the measurement data. Contamination of ballast layer binds water. Due to its electrical conductivity, water significantly attenuates and reflects radar waves, which on the one hand enables the detection of mud spots, but on the other hand limits the achievable measurement depth. This results in a depth scale of either 0 to 6 m, so in perfectly dry condition we reach 6 m, reality shows that 2 to 2.5m is realistic.
Sample Distance
The optimal sampling rate of 4 cm has been validated through ten years of empirical testing by RTA. Additionally, it is recommended to aggregate the data per sleeper compartment for effective maintenance planning. Naturally, the sampling distance impacts driving speed: more samples mean more data and increased CPU load in less time. We support speeds of up to 270 km/h with a 12 cm sampling distance, which still provides 4 samples per sleeper—sufficient for high-quality data analysis and key performance indicator determination.