Using full‐waveform techniques to understand lysimeter‐induced effects on ground penetrating radar measurements

Abstract

Lysimeters are widely used to investigate soil‐plant‐atmosphere interactions and to assess the impact of management practices on water and nutrient fluxes. These interactions and fluxes are strongly impacted by local scale variability in soil water content and soil hydraulic properties. However, centimeter‐scale imaging of subsurface processes and the controlling variables such as soil water content remains challenging, and conventional approaches often rely on simplifying assumptions that smooth heterogeneities. This study presents a theoretical investigation of full‐waveform ground penetrating radar (GPR) modeling for cylindrical lysimeters, with the objective of assessing the lysimeter‐induced effects on GPR data and their implications for data analysis and inversions. Numerical experiments were conducted for three scenarios: homogeneous dry and saturated sand, heterogeneous soil, and a simplified experimental model, using different antenna frequencies and explicitly accounting for the three‐dimensional lysimeter geometry. The results demonstrate that incorporating the cylindrical geometry is essential, particularly for dry soil conditions and high‐frequency data. The modeled wavefields reveal strong interference among direct, reflected, and refracted waves, consistent with observations from experimental GPR data. While wave‐type distinction is more straightforward in saturated soils, increased attenuation limits signal penetration. A simplified layered model inside the lysimeter geometry was used to reproduce dominant observed features of experimental data from a layered sand‐filled lysimeter, providing a robust foundation for future FWI applications in lysimeter studies.