Diurnal Measurement of Near-Surface Water Content using Ground Penetrating Radar (GPR)-Implications for Large Scale Hydrological Studies using Radar Measurements

Ground-penetrating radar (GPR) was utilized to measure near surface diurnal soil reflectivity and dielectric properties to determine change in soil water content. Measurements were performed over both bare and vegetated surfaces. From these measurements, soil volumetric water contents were determined via surface reflectivity and in one instance from propagation time. Soil water content was ground truthed gravimetrically. Measurements show that water content changes at the surface follow patterns reported by Jackson (1973), albeit that changes in the soil profile as measured from propagation time data may follow a different pattern. Diurnal variations in soil reflectivity do not show evidence for increases in bulk soil dielectric permittivity due to thermodielectric bound water desorption effects as air and soil temperatures appear to have been too low to induce desorption of bound water layers. Results here suggest that continuous monitoring of soil dielectric properties and water content would improve the accuracy of large-scale SAR and scatterometer measurements. Furthermore, such data should be used to correct for differences between soil water content at the time of gravimetric sampling and the time of radar measurement