Module 2.3: How GPR works internally

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Ground Penetrating Radar (GPR) block diagram

The following diagram shows the main components of a Ground Penetrating Radar system, you can see that it contains all of the components of a standard Radar system with a few small differences.

Ground Penetrating Radar (GPR) block diagram

The following diagram shows the main components of a Ground Penetrating Radar system, you can see that it contains all of the components of a standard Radar system with a few small differences.

Block diagram of a GPR (Ground Penetrating Radar)
Block diagram of a GPR (Ground Penetrating Radar)

The main differences are that there is no duplexer present in a GPR and the reason for that is because there are (usually) separate antennas for transmitting and receiving, these are almost always housed within a single box which is referred to as the ‘antenna’. The synchroniser (clock) is contained within the control box and GPR has a wheel to tell the radar when to trigger.

The following diagram shows where these items might be found on a typical GPR system (the GPR for this example was based on the IDS Detector Duo, now discontinued, but the same components are contained in almost all GPR from all manufacturers).

Diagram showing the locations of the different parts of a typical GPR system
Diagram showing the locations of the different parts of a typical GPR system

As with the traditional radar, it is useful to have a look at the sequence required for a GPR to transmit and to receive a signal, starting the output section (transmit).

Ground Penetrating Radar (GPR) output section

  1. GPR is driven by a controlling system that runs on its native computer
  2. When the GPR is pushed forward the wheels of the trolley turn, this causes the encoder wheel (mounted against the trolley wheel) to turn.
  3. A signal is sent from the encoder wheel to the control box, informing the controller that the GPR is moving forwards.
  4. The control box then tells the transmitter to generate a pulse.
  5. The pulse is sent from the transmitter, through the antenna, into the ground. The synchroniser then starts to measure the time delay from the moment the pulse is transmitted, until any potential reflections are received.
  6. The GPR now switches to ‘listen’ mode.

Ground Penetrating Radar (GPR) input section

  1. Any reflections from the received signal are collected by the GPR antenna
  2. These reflections are very small, they are immediately passed to the receiver which is usually mounted directly on top of the antenna.
  3. In the receiver, the reflections are amplified (made larger).
  4. The amplified reflections travel from the receiver to the control box where the synchroniser (internal clock) has been measuring the timer delay since those reflections were sent.
  5. A response is shown on the display.

The full cycle (input and output sections) is repeated for every ‘click’ of the survey wheel.

Our Most Common Questions

Frequently Asked Questions

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What can a Ground Penetrating Radar survey detect?

With GPR, you can detect a wide range of objects below ground level, including both metallic and non-metallic objects such as plastic pipework. GPR will also identify and map any voids below the surface, such as air pockets or mine shafts, as well as any other irregularities including concrete and previously excavated or back-filled areas.

Will GPR compromise safety on my site?

GPR equipment emits an electromagnetic pulse into the ground and records the reflected signals from subsurface structures and voids. It is entirely non-destructive and will not break the ground’s surface or affect any objects below. What’s more, it doesn’t emit any harmful levels of radiation, nor are there any other by-products created throughout the process. This means it’s entirely safe to use by its operators, and on sites of any type, including those open to the public.

Is a GPR survey 100% accurate?

While GPR is one of the most effective methods of non-destructive testing available, it can never be 100% accurate. One factor that can adversely affect the accuracy levels include the type of soil being surveyed. Clay soils and soils that contain high levels of salt or minerals can obstruct the GPR reading. Another factor is the experience of the equipment’s operator: interpreting the data collected can be complex, which is why it’s beneficial to commission surveys from an expert firm.

Is GPR equipment difficult to use?

The equipment itself is not difficult to use, but the interpretation of the data recorded tends to be complicated. The results of a GPR survey aren’t automatically translated into an easy-to-understand picture of what lies below the surface; instead, it’s a series of lines and waves and it can take both training and years of practice to master the art of correctly reading the output. Often, it is the experience of the equipment’s operator that plays the most significant role in the accuracy of the results GPR can achieve.

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