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Time Domain Reflectometry Range of Accuracy for High Surface Area Soils

National Soil Tilth Laboratory, 2150 Pammel Dr., Ames, IA 50011

View larger version (16K): [in a new window]   Fig. 1. Specific surface area for the different depths of Sites 1, 2, 3, and 4.

View larger version (16K): [in a new window]   Fig. 2. Comparison of bulk densities for field sites and corresponding repacked laboratory calibration.

View larger version (19K): [in a new window]   Fig. 3. Laboratory waveforms for (a) Site 3, 43-cm depth, 0.326 m3 m–3 and for (b) Site 4, 96-cm depth, 0.379 m3 m–3.

View larger version (18K): [in a new window]   Fig. 4. Field data for Site 3, 35-cm depth, 1996 season, showing good quality TDR data.

View larger version (18K): [in a new window]   Fig. 5. Field data for Site 1, 58-cm depth, 1996 season, showing noisy TDR data.

View larger version (20K): [in a new window]   Fig. 6. Fairly good agreements between laboratory and field raw data for (a) Site 3, 35-cm depth, but field data were offset to higher values for (b) Site 4, 35-cm depth. The laboratory excludes data points with incorrect internal waveform analysis, and only the good field data were included in the calibration.

View larger version (27K): [in a new window]   Fig. 7. Comparison of measured and calculated water content for laboratory data showing each site-depth regression (overlapping) without and with a temperature correction, and compared with Topp's (1980) equation.

View larger version (34K): [in a new window]   Fig. 8. Comparison of measured and calculated water content for field data showing each site–depth regression (overlapping) without and with a temperature correction, and compared with Topp's (1980) equation.

View larger version (19K): [in a new window]   Fig. 9. Calculated water content from TDR, with and without a temperature term, and water content from neutron probe for 1996, Site 3, 35-cm depth.

View larger version (23K): [in a new window]   Fig. 10. Calculated water content from TDR, with and without a temperature term, and water content from neutron probe for 1996, Site 1, 58-cm depth.

View larger version (21K): [in a new window]   Fig. 11. Calculated water content from TDR, with and without a temperature term, and water content from neutron probe for 1997, Site 1, 58-cm depth.