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