Time-frequency approach for ground penetrating radar data analysis to assess railroad ballast condition

Railroad ballast plays an important role in supporting heavy rail loading, preventing the deformation of track, and providing drainage of water from the track structure. However, over time, ballast is fouled by the breakdown of ballast aggregate and/or the infiltration of fines, which undermine ballast functions. This may result in damage to the rail system, such as track settlement. Ground penetrating radar (GPR), a nondestructive method, can be used to rapidly, effectively, and continuously assess railroad track substructure conditions. Ballast under various fouling conditions generates various electromagnetic (EM) scattering patterns. In this study, air-coupled 2 GHz antenna was found to be sensitive to the scattering pattern change. Appropriate data processing was used to remove the effects of ties and rails to obtain clear GPR images of the subsurface layers. Then, the amplitude envelope and time-frequency approaches were implemented to characterize the signal in time and frequency domains simultaneously. Using these techniques, non-fouled ballast thickness can be assessed and trapped water can be detected, along the track.