Mapping surface soil water content with the ground wave of ground-penetrating radar

We investigated the accuracy of surface soil water content measurements with the ground wave of GPR. We examined the influence of SWC mapping equipment near the GPR and tested the significance of reported time differences in air and ground wave arrival time at zero antenna offset (t(0)). The influence of the equipment on the radar signal was tested by introducing the sleds, odometer and vehicle to pull equipment stepwise. The sleds caused a decrease in the amplitude of the ground wave and all the equipment caused disturbances in the air wave. However, the data quality remained sufficient to pick arrival times automatically. The importance of t(0) was assessed with 20 WARR measurements and a sensitivity analysis based on GPR simulations. We observed a mean t(0) of 0.5231 ns that could not be explained from the GPR simulations. There also was a large variation in t(0), but that could be explained by considering picking error, positional error and soil water content heterogeneity in the sensitivity analysis. We conclude that a t(0) correction in the calculation of soil water content would improve measurements with GPR, but it should be noted that the large variation in t(0) makes it difficult to accurately estimate mean t(0).