Two- and three-parameter calibrations of time domain reflectometry for soil moisture measurement

C. Yu, A. W. Warrick, M. H. Conklin, M. H. Young, Marek G Zreda

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

Time domain reflectometry (TDR) is widely used to measure and monitor soil water. The commonly used calibration curve is the third-degree 'universal polynomial' of Topp et al. [1980]. The most common refinement is calibration to a specific soil but still using four parameters (coefficients)from fitting a third-degree polynomial. Here we demonstrate that a three-parameter expression, θ(v) = aK(a)/α + b, fits as close as or more closely than the four-parameter polynomial (where the three parameters a, b, and α are determined by fitting water content θ(v) to the dielectric coefficient K(a)). This form is consistent with the well-known mixing model. For an isotropic soil with homogeneous water distribution this expression is further simplified to two parameters by taking α = 0.5. When α is 0.5, its calibration is equivalent to the linear calibration between θ(v) and the travel time along the waveguide. In addition, the simple three-parameter expression can be easily inverted without losing accuracy with regard to the original calibration. The TDR calibration expressed in a three-parameter form not only achieves a good fit but also conveys a physical connotation.

Original languageEnglish (US)
Pages (from-to)2417-2421
Number of pages5
JournalWater Resources Research
Volume33
Issue number10
StatePublished - Oct 1997

Fingerprint

time domain reflectometry
Soil moisture
calibration
soil moisture
soil water
Calibration
Polynomials
Soils
Water
water distribution
Travel time
travel
Water content
parameter
soil
Waveguides
travel time
water content
monitoring

ASJC Scopus subject areas

  • Aquatic Science
  • Environmental Science(all)
  • Environmental Chemistry
  • Water Science and Technology

Cite this

Two- and three-parameter calibrations of time domain reflectometry for soil moisture measurement. / Yu, C.; Warrick, A. W.; Conklin, M. H.; Young, M. H.; Zreda, Marek G.

In: Water Resources Research, Vol. 33, No. 10, 10.1997, p. 2417-2421.

Research output: Contribution to journalArticle

Yu, C. ; Warrick, A. W. ; Conklin, M. H. ; Young, M. H. ; Zreda, Marek G. / Two- and three-parameter calibrations of time domain reflectometry for soil moisture measurement. In: Water Resources Research. 1997 ; Vol. 33, No. 10. pp. 2417-2421.
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