Cablibration of column-attaching TDR probe based on dielectric mixing model
2006
Miyamoto, H.(Kyushu Univ., Fukuoka (Japan)) | ; Chikushi, J.
A column-attaching TDR probe (CA probe) was designed to minimize the effect of disturbance on soil matrix during soil-water measurement, and was calibrated using sand for various water contents (theta). Relative dielectric constant for sand increased with water content, and finally reached to 12.7 at saturated condition. Compared with estimate by Topp equation (Topp et al., 1980), smaller relative dielectric constants were observed at all water contents in case for the CA probe. The relative dielectric constants measured by the CA probe should be composite relative dielectric constant (epsilon(T)) of 2 components in sampling volume: medium (epsilon(m)) and acrylic part (epsilon(ac)). To evaluate the effect of acrylic part on epsilon(T), contribution of both components was investigated with data sets of relative dielectric constant for ethanol having various concentrations, based on dielectric mixing model (epsilon(T)=(omegaepsilon(m)alpha+(1-omega)epsilon(ac)alpha)**(1/alpha);where omega and alpha are parameters). Combined Topp equation, substituting epsilon(m) in the equation by the estimate from the mixing model, relatively agreed with observed epsilon(T) at various theta. The determination of mixing model parameters (omega and alpha) with ethanol could make it possible to calibrate epsilon(T) vs. theta easier than that with soil.
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