About Us | Help Videos | Contact Us | Subscriptions
 

Abstract

 

This article in SSSAJ

  1. Vol. 67 No. 2, p. 478-482
     
    Received: July 30, 2002


    * Corresponding author(s): magnus.persson@tvrl.lth.se
 View
 Download
 Alerts
 Permissions
Request Permissions
 Share

doi:10.2136/sssaj2003.4780

Estimating Water Content from Electrical Conductivity Measurements with Short Time-Domain Reflectometry Probes

  1. Magnus Persson * and
  2. Sahar Haridy
  1. Department of Water Resources Engineering, Lund University, Box 118, SE-221 00 Lund, Sweden

Abstract

Time domain reflectometry (TDR) is a widely used technique for measuring the dielectric constant (K a) and bulk electrical conductivity (σa) of soil. The K a measurement can be converted to water content (θ) by means of a (soil specific) calibration. Since the accuracy of the K a measurement is dependent on the TDR probe length, probes longer than about 0.1 m are preferred. However, shorter probes are desired for many applications. The possible use of the σa measurement of short TDR probes for estimating θ under conditions with constant soil solution electrical conductivity (σw) is investigated and the accuracy of the K a and σa measurements of two reference TDR probes (0.20 m long) and four miniature probes (0.02 m long) is determined. The standard deviation of the K a measured by the miniature probes was found to be ten times higher compared to the reference probes. The standard deviation of the σa measured by the miniature probes was only slightly larger compared with the reference probes. A calibration experiment in sand using the reference TDR probes showed that when σw is constant, the θ estimations from K a and σa measurements have the same accuracy. TDR measurements were taken with the miniature probes in small sand samples. From the K a–θ and σa–θ relationships determined in the calibration experiment, the K a and σa measurements of the miniature probes could be converted to θ. The root mean square error (RMSE) of the θ estimated by the K a measurements was 10 to 20 times higher compared with the reference probe measurement. The RMSEs of the θ estimated by the σa measurements was only two to three times higher compared with the reference probes. The results presented in this study clearly show that the σa measurement made with short TDR probes can give accurate θ estimations under conditions of constant σw

  Please view the pdf by using the Full Text (PDF) link under 'View' to the left.

Copyright © 2003. Soil Science SocietyPublished in Soil Sci. Soc. Am. J.67:478–482.