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Quantifying the Impact of Soil Properties on the Performance of Electromagnetic Water Content Sensors
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: 2009 Reno, Nevada, June 21 - June 24, 2009 097437.
Authors: Congying Wang, Ricardo Estevez, Carlos M.P Vaz,, Scott B Jones
Keywords: Electromagnetic, water content sensor, dielectric, permittivity, Network analyzer.
Most water content sensors today rely on soil dielectric properties and measure using electromagnetic (EM) techniques. This includes for example time domain reflectometry (TDR), ground penetrating radar (GPR) and remote sensing measurements, etc. There are many different soil water content sensors available with orders of magnitude difference in price, suggesting significant differences in quality. Our objective was to highlight key factors that impact soil water content measurements using EM sensors and to develop a standard technique for evaluating the performance of EM sensors, especially to find or design a reference relaxing-conducting (R-C) system capable of providing variable electrical conductivity and relaxation frequency, which represent the most challenging measurement conditions in soils. We used network analyzer measurements to provide well-defined dielectric permittivity standards with which to characterize EM sensors. We evaluated a 50 MHz EM sensor using liquids and suspensions developed in this study which exhibit well-defined permittivity and variable electrical conductivity properties. The effective frequency analysis and error evaluation were conducted on the Hydra Probe testing results. The methodology is aimed at providing quantitative measures of sensor performance encompassing a wide variety of soil and porous media conditions.