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United States Department of Agriculture

Agricultural Research Service

Title: Dielectrics - Beyond Water Content

Author
item Logsdon, Sally

Submitted to: First International Symposium on Soil Water Measurement Using Capacitance Impedance and Time Domain Transmission
Publication Type: Proceedings
Publication Acceptance Date: November 8, 2002
Publication Date: November 26, 2003
Citation: LOGSDON, S.D. DIELECTRICS - BEYOND WATER CONTENT. FIRST INTERNATIONAL SYMPOSIUM ON SOIL WATER MEASUREMENT USING CAPACITANCE IMPEDANCE AND TIME DOMAIN TRANSMISSION. 2003. CD-ROM. LAUREL, MD: PALTIN.

Technical Abstract: To properly understand dielectric methods for determining soil water content, it is necessary to study the frequency relation of the complex dielectric properties, known as dielectric spectroscopy. The objectives of this study are to see if dielectric spectroscopy can explain the observed dielectric patterns from time domain reflectometry (TDR)for a problem soil, and to show how dielectric spectroscopy can be used to determine other soil properties. Mixing models were used with data from another study to back-calculate a range of complex spectra for bound water. Complex dielectric spectra were measured for a problem soil. The frequency analysis of the real and imaginary dielectric components were used to calculate the square root of the apparent dielectric number, ADN, which is the measured value from TDR and impedance dielectric systems. The ADN back-calculated for bound water increased 59% at a frequency of 0.1 GHz compared with that for the square root of the real dielectric at 1 GHz frequency. As the temperature increased from 10 to 35 degrees C, ADN decreased 2% at 1 GHz, but increased 17% at 0.1 GHz. The ADN determined from TDR was much greater than that calculated at equivalent frequencies from dielectric spectra. Calculated viscosities and diffusion coefficients for bound water showed reduced mobility and increased viscosity for bound water compared with free water. The next generation of dielectric sensors should consider quantifying these other properties in addition to, or in place of, soil water content.

Last Modified: 9/22/2014
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