Earth Surface Controlled Wavefields in Ground-Penetrating Radar Responses

Abstract Ground-penetrating radar (GPR) data are commonly collected with the transmitting and receiving antennas in close proximity. Small transmitter – receiver offsets mean the direct waves can dominate or even saturate the receiver, masking near-surface target responses and potentially leading to misinterpretation. Also, GPR data are interpreted under the implicit assumption that recorded reflections originate from subsurface targets and that the recorded events' moveout velocity discriminates between airwave and groundwave responses. The presence of the air – ground interface significantly alters the antenna radiation pattern and introduces complex wave components, such as head waves and evanescent waves, that interact with objects both above and below the ground surface. These other signal paths make this assumption incomplete, as demonstrated by theoretical, numerical and field studies. In this study, we investigate how the radiation pattern of a horizontal electric dipole placed on the air – ground interface governs the excitation of various wavefields, present in the GPR recorded data. Numerical results confirm that vertically oriented above-ground structures can generate hyperbolic events with groundwave velocity, while shallow subsurface targets may exhibit airwave velocity characteristics. This paper extends our previous work findings by examining the spatial distribution of electromagnetic (EM) signals around a transmitter and those that reach the receiver. The results demonstrate that antenna orientation controls and changes direct-wave amplitudes, clarify the physical origin of the so-called “phantom” targets in GPR records, and provide survey-design guidelines for minimizing misinterpretation in complex near-surface environments.