Applying different features of GPR hyperbolic reflections to refine cavity identification in a complex environment

Abstract Ground penetrating radar (GPR) is a widely used geophysical technique for detecting subsurface features in near-surface investigations. Subsurface cavities present severe geotechnical hazards, particularly in post-mining areas where collapse-prone strata threaten public safety. This study evaluates the effectiveness of GPR for detecting such cavities within a geologically complex region previously subjected to lignite excavation in Várpalota, Hungary. A total of 30 GPR profiles were acquired using 200 and 270 MHz antennas across hiking trails and collapsed zones. The profiles revealed numerous hyperbolic reflections interpreted as potential cavities. Numerical simulations using GprMax were employed to validate field interpretations and examine the influence of dielectric contrasts, depth, and material properties on the radar signal response. In total, 64 subsurface cavities were identified. The potential risk of the cavities was analysed based on two factors: how deep they are and their position relative to a subsurface interface. Of these, 77% were located below a subsurface interface, showing a dominant NW–SE trend likely controlled by structural features. Shallow cavities in these zones pose a moderate risk of long-term instability, targeted mitigation. The findings emphasize the diagnostic value of combining GPR with electromagnetic modeling for hazard mapping in high-risk terrain and highlight optimal strategies for antenna selection, velocity estimation, and interface-aware interpretation. The approach of integrating GPR with numerical models can be further refined for broader application in geotechnical and environmental studies.