Comparison of ground penetrating radar and time-domain reflectometry as soil water sensors

Robust and noninvasive techniques for in situ measurement of soil water content are essential for monitoring and research of many hydrologic processes. Although in situ measurement of soil water content by means of a soil's electric and dielectric properties has been explored extensively, the use of ground-penetrating radar (GPR) for this purpose is not well established. We compared the soil's dielectric constant as measured by GPR and time domain reflectometry (TDR) and its relationship to water content determined independently in auger holes. We propose a calibration equation relating soil water to GPR-measured dielectric constants. The difference in calibration equations between GPR and TDR was partially attributed to the difference in frequency ranges in which TDR and GPR operate and the zero offset of the GPR.