Time-lapse 3D GPR imaging of brilliant blue infiltration experiments

Preferential flow due to fingering, funnelling or macropore flow results in small scale spatial variability in infiltration. On the plot scale (∼ 1 m × 1 m), a common method to characterize such infiftration patterns are sprinkling experiments using dye tracers. Typically, the resulting patterns are analyzed after excavation using digital photographs of selected vertical 2D slices. The observed preferential flow paths vary in scafe from centimeters to decimeters width, often reveafing rather compficated 3D flow networks. In this study, we examine the potential of surface based 3D ground-penetrating radar (GPR) to image subsurface flow patterns from such dye tracer experiments. Our approach is based on time-tapse 3D (i.e., 4D) GPR surveys using 500 MHz antennas. In a case study, we compare the resufts from our GPR-based imaging approach to the patterns observed in digitaf photographs after excavation. Our resuits show that GPR is a feasibie technique to non-invasiveiy image major flow patterns in 3D and, compared to the ctassicaf invasive approach, provides the opportunity to image the temporat evofution of the associated infiltration patterns.