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Conjunctive Use of Tension Infiltrometry and Time-Domain Reflectometry for Inverse Estimation of Soil Hydraulic Properties

Conservation and Production Research Laboratory, USDA-ARS, P.O. Drawer 10, Bushland, TX 79012-0010

View larger version (32K): [in a new window]   Fig. 1. Diagonally placed time-domain reflectometry (TDR) probes shown in a vertical cross section of the cylinder (above) and horizontally placed TDR probes shown in a horizontal cross section (below).

View larger version (16K): [in a new window]   Fig. 2. Measured wetting water characteristic data and corresponding optimized solutions (Table 2). Error bars represent 95% confidence intervals for 13 extracted cores. Water characteristic data at the two largest pressure heads (-65 and -115 mm) were not included in the objective function for these optimizations. , volumetric water content.

View larger version (33K): [in a new window]   Fig. 3. Measured cumulative infiltration and water contents () and the corresponding optimized piecewise (3.1a, 3.2a, and 3.3a) and van Genuchten-Mualem (VGM) (3a) solutions for Exp. 3. Predicted diagonal time-domain reflectometry water contents are also shown for optimizations 3.1b, 3.2b, and 3.3b (see Table 2). Note that the piecewise solution is not always discernible from the VGM solution. Error bars are 95% confidence limits. Arrows indicate a step change in the infiltrometer supply pressure.

View larger version (23K): [in a new window]   Fig. 4. Influence of assumed averaging depth on optimized parameters and predicted water contents for the diagonally placed time-domain reflectometry probe at early times. Error bars are 95% confidence intervals. , volumetric water content; n and , empirically fitted parameters; Ks, saturated hydraulic conductivity; and K(hp1), hydraulic conductivity at h = hp1.

View larger version (45K): [in a new window]   Fig. 5. Two-dimensional progression of wetting front (Optimization 3.1a) and corresponding time-domain reflectometry waveforms for a diagonally (30°) placed probe. The diagonal line represents the center rod of a trifilar probe.

View larger version (61K): [in a new window]   Fig. 6. Simulated cross section of water contents () at t = 614 s (Optimization 3.1a) in Cartesian coordinates at several positions along the x-axis that runs parallel with the time-domain reflectometry (TDR) rods. The filled circles represent the positions of the TDR probes and the border between the white and filled regions represents the soil surface boundary.