Monitoring water infiltration in aggregated volcanic ash soil using multi-offset GPR

Abstract:

Ground penetrating radar (GPR), one of the electromagnetic (EM) exploration techniques, is regarded as an effective method to monitor soil water infiltration process in rapid and non-destructive fashion. From EM wave velocity data, we can estimate dielectric permittivity of the soil. The dielectric permittivity is then used to calculate volumetric water contents from one of empirically derived equations relating dielectric permittivity and volumetric water content. In many GPR surveys, wide angle reflection and refraction (WARR) or common midpoint (CMP) survey techniques with a pair of GPR antennas are used to obtain EM wave velocities. WARR and CMP, however, are not suitable to monitor dynamic processes, such as soil water infiltration processes, as it takes time to complete each survey.

A multi-offset (MO) GPR survey technique allows one to obtain EM wave velocity profiles in short time by scanning soil profiles with multiple GPR antennas. In this study, the MO GPR survey was used to monitor changes in soil water content distribution during infiltration test. A field experiment was conducted at an experimental field at Tokyo University of Agriculture and Technology where top soils consisted mainly with well aggregated volcanic as soils. The GPR system used in this study was composed of a transmitter and multiple receivers of 250 MHz GPR. Ground truth of soil water content was obtained simultaneously with soil moisture sensors such as Profile Probe.