HR: 0830h
AN: H31B-0458    [PDF]
TI: Soil Moisture Content Estimation using GPR Reflection Travel Time
AU: * Lunt, I A
EM: ilunt@lbl.gov
AF: Department of Civil Engineering, UC Berkeley, Berkeley, CA 94720 United States
AU: Hubbard, S S
EM: sshubbard@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Rubin, Y
EM: rubin@ce.berkeley.edu
AF: Department of Civil Engineering, UC Berkeley, Berkeley, CA 94720 United States
AB: Ground-penetrating radar (GPR) reflection travel time data were used to estimate changes in soil water content under a range of soil saturation conditions throughout the growing season at a California winery. Data were collected during four data acquisition campaigns over an 80 by 180 m area using 100 MHz surface GPR antennae. GPR reflections were associated with a thin, low permeability clay layer located between 0.8 to 1.3 m below the ground surface that was calibrated with borehole information and mapped across the study area. Field infiltration tests and neutron probe logs suggest that the thin clay layer inhibited vertical water flow, and was coincident with high volumetric water content (VWC) values. The GPR reflection two-way travel time and the depth of the reflector at borehole locations were used to calculate an average dielectric constant for soils above the reflector. A site-specific relationship between the dielectric constant and VWC was then used to estimate the depth-averaged VWC of the soils above the reflector. Compared to average VWC measurements from calibrated neutron probe logs over the same depth interval, the average VWC estimates obtained from GPR reflections had an RMS error of 2 percent. We also investigated the estimation of VWC using reflections associated with an advancing water front, and found that estimates of average VWC to the water front could be obtained with similar accuracy. These results suggested that the two-way travel time to a GPR reflection associated with a geological surface or wetting front can be used under natural conditions to obtain estimates of average water content when borehole control is available. The GPR reflection method therefore has potential for monitoring soil water content over large areas and under variable hydrological conditions.
DE: 0694 Instrumentation and techniques
DE: 1842 Irrigation
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2003 Fall Meeting