Soil water content measurements at different scales: accuracy of time domain reflectometry and ground-penetrating radar

Accurate measurements of soil water content with an appropriate support are important in many research fields. Ground-penetrating radar (GPR) is an interesting measurement technique for mapping soil water content at an intermediate scale in between point and remote sensing measurements. To measure soil water content with GPR, we used the velocity of the ground wave, which is the signal traveling directly from source to receiving antenna through the upper centimeters of the soil. To evaluate GPR performance, we aggregated time domain reflectometry (TDR) and gravimetric soil water content measurements to the support of GPR measurements. The results showed that the calibration equations between GPR measurements and aggregated gravimetrical soil water content were similar to those obtained for TDR measurements, suggesting that available TDR calibrations (e.g. Toppʹs equation) can be used for GPR. Furthermore, we found that the accuracy of GPR to measure soil water content is comparable with the accuracy of TDR, although it depended on the type of data acquisition used for the determination of the ground wave velocity.