3D Ground Penetrating Radar
What is it?
Step-frequency GPR array system (3DGPR) is a ground penetrating radar system consisting of a series of 
frequencies. The 3DGPR system that MnDOT uses contains 21 pair antennas at 3 in spacing that has a total width of 5 ft. Compared to traditional single channel horn antenna GPR systems, which only provides pavement information on a longitudinal line for a single survey pass, the 3DGPR can cover 5ft width of pavement area for a single survey pass. Thus, it is more efficient than single antenna system for roadway evaluation and can provide three-dimensional view of roadway features. The radar measures the phase and amplitude on each frequency and used an inverse Fourier transform of these data to build a time domain profile (A-scan).
Therefore, the step-frequency radar collects data in the frequency domain and converts the data to time-domain data through computer processing. The computer control allows the user to set the dwell time on each frequency as well as the start and stop frequencies.
What type of information it provides
- Transversal and longitudinal pavement layer thickness profiles.
- Detection of underground anomalies.
- Potential detection of asphalt mixture stripping.
- Potential use for moisture monitoring in the surface and base layers.
What are its intended applications?
MnDOT’s 3DGPR system is a loan from FHWA. MnDOT has used for pavement layer thickness evaluation based on district request. As a part of SHRP R06D assistance program, MnDOT evaluated a potential application of using the 3DGPR to detect asphalt mixture stripping.
Project applications: The research office has been providing services to districts for pavement layer thickness evaluation and detection of underground anomalies, such as voids, steel mash, and underground pipes with unknown locations, etc.
Research applications: The 3DGPR radar will be incorporated into the Road Doctor vehicle to further advance the ongoing research on using the 3DGPR technology along with other continuous roadway evaluation technologies, such as thermal imagine and Traffic Speed Deflectometer (TSD) to effectively detect stripping in asphalt pavements.