Ground-penetrating radar for correlation analysis of temporal soil moisture stability and land-slope

Knowledge of temporal surface soil moisture variability is an useful key in agriculture, surface hydrology and meteorology. In that respect, ground-penetrating radar (GPR) is a non-invasive and promising tool for high-resolution and large scale characterization. In the case of quantitative analysis, off-ground GPR signal modeling and full-waveform inversion has shown a great potential during the last decade. In this research, we applied GPR for time-laps measurements in an agricultural field along a 320 m single transect with a significant land-slope for about 3 months. A 200-2000 MHz TEM-horn antenna situated 1.1 m above the ground, connected to a vector network analyzer (VNA) was used as an off-ground frequency-domain GPR. The accurate positioning was done using a differential GPS. All systems were mounted on a 4-wheels vehicle for realtime and automated mapping. The calibration of the antenna and using the GPR signal inversion permitted to the ground surface relative dielectric permittivity. Topp's model was used for transformation of the relative dielectric permittivity to soil moisture. The temporal stability of the field-average soil moisture was computed by indicators based on the relative difference of the soil moisture to the field-average. The results showed an excellent correlation amount of -0.9905 for temporal stability of soil moisture and slope variability.