The Necessary Paradigm Shift
Concrete Scanning VS Other GPR Applications
*This article was written for those who are familiar with GPR, others may find it difficult to follow.
GPR has been around for a while and it has many applications. While we aren't familiar with all of the them, we would be surprised if another field produced more complicated radargrams than the concrete scanning industry. Those who are familiar with GPR know just how convoluted radargrams (graphical representation of radar data) can appear when the slab/wall is "busy" with embedments.
The old paradigm, while incorrect, was correct enough times to be adopted. More precisely, the flawed interpretations simply weren't discovered or important enough to matter because the material being scanned wasn't excavated (or cored or cut out). When it was cut out and found to be wrong, it was blamed on the limitations of GPR, or "reflections", "shadows", "interference", and so on. There was no need for a deeper understanding, the limit of the technology was accepted.
If a new paradigm was going to be discovered, it would surely be in the concrete scanning industry. Not only do we have more shapes per radargram, we collect so many more of them than anyone else. While others might collect their data in a preset pattern and review the data at a later time, we collect hundreds of feet of radargrams from all angles in just a few scans. It's very easy for us to make another sweep with the antenna just one inch off from the last one we didn't really like. In addition to that, our margin of error is very small compared to others. They need a better paradigm, but we really need a better paradigm!
GPR Myths, Misconceptions, And Malarkey
Water Flowing Around An Object
Let's start with malarkey. The hyperbola has a similar shape to flowing water being deflected by an object. The shapes look alike... and that's about it. It makes absolutely no sense in terms of radar. We could dissect this in so many ways to prove that it's wrong that this whole article would be 5 times longer. Let's just take one.
Radar works like the following: radio waves are emitted from a transmitter (TX) antenna, reflected off an object, and absorbed by a receiver (RX) antenna. The idea behind the flowing water model is that the wave propagation from the TX antenna behaves like water.
Thankfully, this isn't a popular paradigm, but there are still some people out there that use it. They can get away with it on easy slabs/walls. And when they encounter a little complexity, they hit what they think are the limits of GPR.
Radar works like the following: radio waves are emitted from a transmitter (TX) antenna, reflected off an object, and absorbed by a receiver (RX) antenna. The idea behind the flowing water model is that the wave propagation from the TX antenna behaves like water.
- How is the hyperbola even recorded? If hyperbolas represent waves that have been deflected and continue past the object, how does the receiver antenna know about them. For a radar wave to be detected by the equipment, it has to make the full round trip: TX antenna -> object(s) -> RX antenna. If the wave doesn't hit the RX antenna, it isn't detected at all.
Thankfully, this isn't a popular paradigm, but there are still some people out there that use it. They can get away with it on easy slabs/walls. And when they encounter a little complexity, they hit what they think are the limits of GPR.
Pop Quiz
Which of the following statements are myths, and which are true:
- The intensity (brightness) of a hyperbola is dependent on the density of the material.
- A line feature (for example, the bottom of a slab) is generated by successive hyperbolas where the tails overlap and cancel each other out.
- A radargram is a 2D representation (a slice) of what is below the sweep line.
- Hyperbola tails create a shadow on the hyperbolas below it, making them harder or impossible to discern.
- The tails of a hyperbola are thinner than the apex because there is less radar energy being reflected at that angle and distance.
- 3D scanning works
The main concept in the old GPR paradigm is that scanning a target (an object) generates a hyperbola and its apex gives you the target's location . While this is often sort of true, it's such a superficial model of GPR that it leaves quite a lot of information uninterpreted, and often leads to misinterpretation. This is used as the first principle from which the radargram is interpreted. Meaning that when interpreting radargrams, technicians are prone to "constructing it" with hyperbolas as the primary building block. The RadRay model, in contrast, uses the "pip" as the primary building block.
Most experienced concrete scanners wouldn't (shouldn't!) fall for the 1st statement, they know it's a myth and they hear it all the time from clients. But they also know that rebar reflects at a higher intensity than plastic conduits of the same size and at the same depth. Rebar is more dense than plastic, but it also has a higher dielectric. So all else being equal, a metal rebar will reflect at a higher intensity than a plastic conduit - because of the higher dielectric, not the higher density. Correlation does not imply causation.
The same can be said for the remaining statements, they're all myths and misconceptions. Some of them have a decent degree of correlation, so many people are convinced they are true.
Most experienced concrete scanners wouldn't (shouldn't!) fall for the 1st statement, they know it's a myth and they hear it all the time from clients. But they also know that rebar reflects at a higher intensity than plastic conduits of the same size and at the same depth. Rebar is more dense than plastic, but it also has a higher dielectric. So all else being equal, a metal rebar will reflect at a higher intensity than a plastic conduit - because of the higher dielectric, not the higher density. Correlation does not imply causation.
The same can be said for the remaining statements, they're all myths and misconceptions. Some of them have a decent degree of correlation, so many people are convinced they are true.
Right Concept Wrong Explanation
Since the old GPR paradigm is more of a collection of disparate concepts that can't be traced back to first principles, you get some concepts that are "somewhat" correct, but the explanation is incorrect.
For example, one of the factors that determines hyperbola width is target depth. The explanation is that the GPR waves propagate in the shape of a cone so the wavefront expands as it travels downwards. Therefore the lower targets will reflect the wave sooner along the antenna's sweep path, thus creating a wider hyperbola. Wait! What!?! Why??? There's a gap in reasoning here. Why would a reflection earlier in the sweep necessarily create a wider hyperbola. It sounds legitimate - a wider tail would mean it's closer to the antenna... maybe that's the correlation, but it's definitely not the causation. If a technician who has assimilated the RadRay model hears a claim like this, they can determine it's false within a couple minutes of working out the problem in their head from first principles (also, there are no cones in the RadRay model, so if a cone is used to explain something, it's wrong!)
For example, one of the factors that determines hyperbola width is target depth. The explanation is that the GPR waves propagate in the shape of a cone so the wavefront expands as it travels downwards. Therefore the lower targets will reflect the wave sooner along the antenna's sweep path, thus creating a wider hyperbola. Wait! What!?! Why??? There's a gap in reasoning here. Why would a reflection earlier in the sweep necessarily create a wider hyperbola. It sounds legitimate - a wider tail would mean it's closer to the antenna... maybe that's the correlation, but it's definitely not the causation. If a technician who has assimilated the RadRay model hears a claim like this, they can determine it's false within a couple minutes of working out the problem in their head from first principles (also, there are no cones in the RadRay model, so if a cone is used to explain something, it's wrong!)
When A Paradigm Collapses
There is so much that the old paradigm can't explain that the only thing most concrete scanners look for are hyperbola apexes and the bottom of slabs. They eventually give up on questions that bothered them in the beginning of their career. Why did the hyperbola tail disappear, why is this line so much brighter than expected, why is it white when it should be black, why is the shadow at the wrong location, why is there a hyperbola there, shouldn't there be a hyperbola here, is that a false positive or a conduit, is that a PT or rebar, what the hell is this, what the hell is that, and so on and so forth. A new paradigm was needed.
The RadRay model explains and predicts so much more of the radargram. It's like turning on a light in a dim room, vague shapes turn into recognizable objects. It's easy to figure out what shapes a target generates (it's rarely a single hyperbola), where they are, why they're there, and why they have their characteristics like shape, color, and intensity. Because the RadRay model starts from first principles, slabs with strange, busy, and unlikely configurations of targets are now possible to decipher. GPR still has its limits, but they've been pushed back. Our training makes it easier to reach those limits.
The RadRay model explains and predicts so much more of the radargram. It's like turning on a light in a dim room, vague shapes turn into recognizable objects. It's easy to figure out what shapes a target generates (it's rarely a single hyperbola), where they are, why they're there, and why they have their characteristics like shape, color, and intensity. Because the RadRay model starts from first principles, slabs with strange, busy, and unlikely configurations of targets are now possible to decipher. GPR still has its limits, but they've been pushed back. Our training makes it easier to reach those limits.
Featured links
Get in touch
-
hello@focuscage.com
Copyright © 2025
Created with
