Complex Permittivity Model for Time Domain Reflectometry Soil Water Content Sensing: II. Calibration

Abstract

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Soil water content on drip irrigated cotton: comparison of measured and simulated values obtained with the Hydrus 2-D model

“…7a, b). Most equipment used to measure soil h, without a field-specific calibration, is generally only accurate to within ±3-5% of soil h (Evett et al 2008;Schwartz et al 2009b). When a field calibration is considered, the accuracy between measured and simulated values of soil h, will probably not improve the values considerably more than what was achieved in this study (2.5% of absolute error).…”

Frequency Domain Probe Design for High Frequency Sensing of Soil Moisture

“…This approach provided Equation (2), which was used to extract the complex permittivity (dielectric constant and dielectric loss) [2]. ε = (β/(sqrt(µ o × ε o )ω(1 + 0.125(tanD) 2 − 5/128(tanD) 4 + 21/1024(tanD) 6 + 429/32768(tanD) 8 ))) 2 ;…”

“…The clay-loam selected for the project was a Pullman clay loam (fine, mixed superactive Torrertic Paleustoll) that was obtained from the surface horizon (0-15 cm). The clay was selected as it was documented to provide measurement difficulties in past research efforts utilizing TDR [6]. The performance of the system was checked against the NPL's reported values for ethylene glycol.…”

“…Recent research has noted errors [2,3] and accuracy limitations of TDR, particularly in heavy soils with high salt contents or with high clay contents [1,4,5]. To mitigate these errors, research efforts have striven to develop algorithmic corrections [6][7][8]. The predominant approach, reported for these algorithms, uses techniques that transform the time-domain waveforms into the frequency domain, to allow for examination of the frequency spectra of the signals.…”

Estimating Soil Water Content from Permittivity for Different Mineralogies and Bulk Densities

“…Because of the involvement of the colloid surface area in the magnitude of dielectric damping, the polarization loss factor is expected to increase with increasing clay content. In general, the predicted surface areas increase with increasing clay contents and measured surface areas (Schwartz et al, 2009a). The complex www.soils.org/publications/sssaj permittivity of bulk and bound water was formulated in the preceding equations as a function of the propagation of sinusoidal plane waves at a single frequency (Schwartz et al, 2009b).…”