Pedosphere 15(6): 805--812, 2005
ISSN 1002-0160/CN 32-1315/P
©2005 Soil Science Society of China
Published by Elsevier B.V. and Science Press
An improved frequency domain technique for determining soil water content
SUN Yu-Rui1, MA Dao-Kun1, LIN Jian-Hui1, P. SCHULZE LAMMERS2 and L. DAMEROW2
1 Department of Information and Electrical Engineering, China Agricultural University, Beijing 100083 (China). E-mail: yurui828@yahoo.com
2 Department of Agricultural Engineering, University Bonn, Bonn 53115 (Germany)
ABSTRACT
      For many years a soil water content sensor with low cost, reliability and sufficient accuracy has been desirable. Thus, an improved measurement method based on the frequency domain (FD) principle for determining soil water content was considered. Unlike other measurement principles, a new measurable index, η, which was independent of the output impedance and the amplitude of the oscillator while relying on the electrical impedance of a multi-pin probe, was proposed. Moreover, a model for processing the impedance of the multi-pin soil probe was developed, and several important electrical parameters for establishing their operating ranges applicable to this probe were evaluated. In order to confirm the theoretical analysis, an experiment was conducted with a 4-pin probe. Using the developed model, the relationship between the proposed index η and soil volumetric water content was shown to be linear (R2 = 0.9921). Thus, as the measurable index, η seemed satisfactory.
Key Words:  dielectric constant, frequency domain principle, measurement, soil water content
Citation: Sun, Y. R., Ma, D. K., Lin, J. H., Schulze, L. and Damerow, L. 2005. An improved frequency domain technique for determining soil water content. Pedosphere. 15(6): 805-812.
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