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Measurement of Soil Water Content with Dielectric Dispersion Frequency
Author(s) -
Xu Jinghui,
Logsdon Sally D.,
Ma Xiaoyi,
Horton Robert,
Han Wenting,
Zhao Ying
Publication year - 2014
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2013.10.0429
Subject(s) - reflectometry , soil water , soil science , dielectric , dispersion (optics) , water content , salinity , soil test , environmental science , soil salinity , materials science , time domain , geology , geotechnical engineering , optics , physics , oceanography , optoelectronics , computer science , computer vision
Frequency domain reflectometry (FDR) is an inexpensive and attractive methodology for repeated measurements of soil water content (θ). Although there are some known measurement limitations for dry soil and sand, a fixed‐frequency method is commonly used with commercially available FDR probes. The purpose of our study was to determine if the soil dielectric spectrum could be used to measure changes in θ. A multifrequency FDR probe was constructed with a 6‐mm diameter, and a soil dielectric spectrum was obtained. Using the dielectric spectrum, the dielectric dispersion frequency ( f d ) was determined. It was discovered that changes in f d were highly correlated with changes in θ, and a third‐order polynomial equation ( R 2 = 0.96) was developed describing the relationship. The effectiveness of f d for θ measurement was evaluated for three soils and a sand across a range of θ. The effects of soil temperature and soil salinity were also evaluated. Accurate measurements of θ were obtained even in dry soil and sand. The root mean square error of the θ estimated by the f d measurement was 0.021. The soil temperature and soil salinity had no measureable effects on θ determination. The use of f d for θ determination should be an effective and accurate methodology, especially when dry soils, soil temperature, and/or soil salinity could potentially cause problems with the θ measurements.