Ground Penetrating Radar systems generally comprise two main components: a control unit, usually including a rechargeable battery to power the system, and antenna.
The control unit contains the electronics that generate and control the GPR pulse of electromagnetic energy waves that the system’s antenna sends into the sub-surface.
The control unit also includes an in-built computer, although some systems use an external laptop. The computer saves the GPR data generated by the antenna’s receiver on disk/solid state memory.
Most control units include an integral display unit. This enables a visual means of configuring the system for the survey. It also displays the GPR data in real time enabling preliminary interpretation of the data on-site and to ensure that the objectives of the survey are met. More detailed analysis is generally undertaken off site by uploading the saved data files and using specialist software to process and interpret the data.
The antenna transmits the GPR signal from the control unit into the sub-surface as a series of pulses. Reflections are produced from changes and features within the sub-surface and these, together with amplitude and time travel information, are received by the antenna. This information is sent back to the control unit, where the information is saved electronically and displayed on screen.
GPR scans can be undertaken using antennas with different central frequencies. The resolution and detail of GPR data increases with higher antenna frequencies; however, the depth of penetration decreases. As a general rule, it is desirable to use the highest frequency possible, while still meeting the objectives of the survey. When undertaking site surveys, we carry a range of antennas which may be suitable for the conditions likely to be encountered. This enables us to select the most suitable antenna. We often scan using multiple frequencies to ensure the best possible data.
There is an increasing number of-all-in one GPR systems available. These typically house the control unit, antenna and power supply all in one unit. Because the component parts are all fixed, the main advantage of these systems is that they are mostly pre-configured and hence simple to use. They are however also very limiting. As the component parts are fixed, they lack versatility and can’t be modified to suit site and survey conditions. For this reason, they tend to be one trick ponies and are designed for a specific survey type.
At Sandberg, we mainly use GPR equipment made by GSSI. The core of our equipment pool that we use daily includes, but is not limited to, the following: