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Near-Surface Water Content Estimation with Borehole Ground Penetrating Radar Using Critically Refracted Waves

Department of Hydrology and Water Resources, University of Arizona. P.O. Box 210110, Tucson, AZ 85721

View larger version (12K): [in a new window]   Fig. 1. Pathways of direct and critically refracted waves from a transmitting borehole ground penetrating radar (BGPR) antenna to a receiving BGPR antenna located a distance, z, below the ground surface and separated by a distance, x. The travel time of the refracted wave is ttx-surface + tair + tsurface-rx. The travel time of the direct wave is tdirect. The critically refracted wave approaches the interface at the critical angle from the normal to the interface, ic.

View larger version (17K): [in a new window]   Fig. 2. Travel times as a function of antennae depth for direct and critically refracted waves for the case of a soil with a velocity of vsoil = 0.1 m ns-1 and an antennae separation of 3 m. The thin lines show the travel times of the direct and critically refracted waves. The first-arriving energy is highlighted as a thick line.

View larger version (16K): [in a new window]   Fig. 3. Schematic diagram of field site used for infiltration experiment showing the locations of borehole ground penetrating radar (BGPR) access tubes (circles), buried time domain reflectometry (TDR) probes (stars), and multilevel TDR probe (square) within the infiltration gallery (solid line).

View larger version (18K): [in a new window]   Fig. 4. Three borehole ground penetrating radar travel time profiles taken before infiltration, immediately after infiltration, and 1 wk after infiltration. The calculated refraction termination depth is shown with a horizontal arrow for each time. The antennae separation was 3.1 m, and the vertical sampling interval was 0.25 m.

View larger version (25K): [in a new window]   Fig. 5. Volumetric water content measured using buried time domain reflectometry (TDR) probes (lines), using direct borehole ground penetrating radar (BGPR) waves at 1.5 m depth (circles), and using the slope of the BGPR travel time profile at the ground surface (squares). TDR4 is located outside of the infiltration gallery at a depth of 1.2 m. TDR2 and TDR3 are located within the gallery at depths of 1.62 and 1.67 m, respectively.