Ground penetrating radar operates by using an antenna to transmit short pulses of electromagnetic energy into a pavement or bridge deck. These pulses are reflected back to the antenna with an arrival time and amplitude that is related to the location and nature of dielectric discontinuities in the material (air/asphalt or asphalt/concrete, reinforcing steel, etc). The reflected energy is captured and displayed as a radar waveform, which contains a record of the properties and thicknesses of the layers within the pavement or bridge deck. Energy amplitudes and dielectric properties are calculated using Infrasense’s winDecar©data analysis software program to output pavement layer thickness, or bridge deck overlay and concrete cover thickness and rebar attenuation.
A typical GPR setup usually includes one or more antennas to transmit and receive the electromagnetic pulses, a data collection unit that collects and stores the data from the antennas, and a computer that controls the data collection unit. The antennas can be either ground-coupled or air-launched, depending on the application. The frequency of the antenna also varies, depending on the application and the type of data required; a high frequency antenna (~1GHz and greater) provides more detail and resolution at a limited depth of penetration, and a low frequency antenna (~400 MHz and less) provides lower resolution data at a greater depth of penetration. The latest version of data collection units allow for higher speed surveys and more antenna configurations to collect large amounts of data efficiently.
Recent GPR systems also use a step-frequency array (3D) covering frequencies ranging from 200MHz to 3000MHz, in both ground-coupled and air-launched setups. These unique arrays provide a much larger amount of data, and require sophisticated analysis software; Infrasense uses its proprietary ExploreGPR software to analyze data from these types of GPR systems.
The most common applications of GPR include:
- Bridge deck condition evaluation
- Pavement structure evaluation
- Utility location
- Concrete inspection (including rebar detection)
- Archeological Surveys