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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: Abstract Only
Publication Acceptance Date: November 8, 2002
Publication Date: November 8, 2002
Citation: LOGSDON, S.D. DIELECTRICS-BEYOND WATER CONTENT. FIRST INTERNATIONAL SYMPOSIUM ON SOIL WATER MEASUREMENT USING CAPACITANCE IMPEDANCE AND TIME DOMAIN TRANSMISSION. 2002. P. 1.3.1-17.

Technical Abstract: To properly understand capacitance probes and time domain reflectometry (TDR), and the effect of operating frequency, it is necessary to study dielectrics as a function of frequency (dielectric spectroscopy). The objectives of this study are to see if dielectric spectroscopy can help interpret dielectric-determination of soil water content, and to show how dielectric spectroscopy can be used to characterize other soil properties. First data from another study was used to back-calculate a range of complex spectra for bound water, using mixing models. This frequency analysis of both real and imaginary components of complex dielectric was used to show the potential inadequacies of TDR (which uses "apparent" dielectric, and the contribution of the imaginary component), and capacitance probes (which operate at a frequency that has a strong positive temperature dependance). TDR and impedance data are then interpreted for "problem" soils (soils with high CEC, high surface area, etc.). Finally dielectric spectra are related to bound water viscosity. Apparent dielectric numbers for bound water were increased up to 30% compared with the real dielectric numbers because of the imaginary component; however, the dielectric numbers determined by TDR were even larger for samples with bound water or high electrical conductivity. Bound water may be an insignificant fraction of many soils, but could be 20% or more of the volume for some soils with high surface area. Perhaps new dielectric sensors should emphasize other soil properties.

Last Modified: 11/25/2014
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