WET sensor performance in organic and inorganic media with heterogeneous moisture distribution

Authors: KARGAS, G - University Of Athens; KERKIDES, P - University Of Athens; Seyfried, Mark; SGOUBPOMILOU, A - University Of Athens

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2012
Publication Date: 7/1/2011
Citation: Kargas, G., Kerkides, P., Seyfried, M.S., Sgoubpomilou, A. 2011. WET sensor performance in organic and inorganic media with heterogeneous moisture distribution. Soil Science Society of America Journal. 75(4):1244-1252.

Interpretive Summary: Interest in electronic monitoring of soil water has grown as increased demand for water creates a greater need for effective water management. Relatively inexpensive commercial soil water sensors that use measured dielectric properties to calculate water content, have been developed to address this need, but have received little independent testing of critical calibration procedures and parameterization. We determined calibration parameters for ten inorganic soils and five organic porous media using the WET sensor (Delta- T Device Ltd. 2005). Measurements in fluids showed that the WET sensor accurately measures dielectric properties. Although the calibration parameters varied with media, we found that excellent calibration could be obtained with all the media tested. In addition, we showed that, when the sensing volume is layered with strongly contrasting dielectric values, the bulk values are determined from arithmetic rather than refractive index averaging. This indicates that the “standard” calibration in uniform media must be used. All the results are consistent with predictions based on the measurement frequency of the instrument, indicating that our results can be generalized to other sensors operating at similar frequencies.

Technical Abstract: Interest in electronic monitoring of soil water has grown as increased demand for water creates a greater need for effective water management. Relatively inexpensive commercial soil water sensors that use measured dielectric properties to calculate water content, have been developed to address this need, but have received little independent testing of critical calibration procedures and parameterization. We determined calibration parameters for ten inorganic soils and five organic porous media using the WET sensor (Delta- T Device Ltd. 2005). Measurements in fluids showed that the WET sensor accurately measures dielectric properties. Although the calibration parameters varied with media, we found that excellent calibration could be obtained with all the media tested. In addition, we showed that, when the sensing volume is layered with strongly contrasting dielectric values, the bulk values are determined from arithmetic rather than refractive index averaging. This indicates that the “standard” calibration in uniform media must be used. All the results are consistent with predictions based on the measurement frequency of the instrument, indicating that our results can be generalized to other sensors operating at similar frequencies.