Evaluating GroundPenetrating Radar use for water infiltration monitoring

Ground-Penetrating Radar (GPR) was used to monitor water infiltration in sand. Water was injected down an 81 cm long tubed hole with a piezometer recording the depth of water and a tap valve used to adjust it to 15 cm ± 2 cm above the bottom of the tube. During the 20 minutes of infiltration two GPR antennas (transmitter and receiver) were recording a trace every second from an offset position on the surface. The signal, enhanced by differential correction allows to trace the evolution of top and bottom limits of the water bulb in space and time. Comparison with hydrodynamic model of the infiltration process proves that the GPR reflections trace the wetting front and not the saturation bulb. An exact, quantified estimation of the evolution of the top border of the wetting zone is provided. For the bottom border, further work on the estimation of the velocity of radar wave in the infiltration bulb will be needed.