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Improved Interpretation of Water Content Reflectometer Measurements in Soils

^a Dep. of Plants, Soils, and Biometeorology, Utah State Univ., Logan, UT 84322
^b USDA-ARS, 800 Park Blvd., Boise, ID 83712
^c Campbell Scientific, Inc., 815 West 1800 North, Logan, UT 84321

View larger version (16K): [in a new window]   Fig. 1. Measured and optimized sensor period P as a function of the relative permittivity for (a) the first CS615 sensor in air, ethanol, and deionized water and (b) the CS616 sensor in air, 2-isopropoxyethanol, deionized water, and 10 mixtures of deionized water and 2-isopropoxyethanol.

View larger version (20K): [in a new window]   Fig. 2. The calculated relative apparent permittivity a as a function of volumetric water content for CS615 sensors in construction sand, Lolalita sandy loam, Searla loam, and Larimer loam. The water content-permittivity relationship according to Topp et al. (1980) is also shown.

View larger version (24K): [in a new window]   Fig. 3. Calculated relative permittivity as a function of volumetric water content for the CS616 sensor, Tektronix TDR, and Hydra impedance probe in a silt loam soil. The water content-permittivity relationship according to Topp et al. (1980) is also shown.

View larger version (23K): [in a new window]   Fig. 4. Calculated period P as a function of water content for (a) the six CS615 sensors and (b) the three CS616 sensors (solid lines), assuming a Topp-like soil with a1 = 0.115 and b1 = –0.176 in Eq. [6]. The water content-period relationships according to the factory calibrations for low-conductivity soils are also shown. Note that some of the solid lines representing the individual sensors almost completely overlap.