Spatial averaging of water content by time domain reflectometry: Implications for twin rod probes with and without dielectric coatings

Paul A Ferre, D. L. Rudolph, R. G. Kachanoski

Research output: Contribution to journalArticle

144 Citations (Scopus)

Abstract

The averaging of apparent relative dielectric permittivities by time domain reflectometry (TDR) is examined for properties varying along TDR waveguides and in the plane perpendicular to a TDR probe. A square root averaging model with uniform weighting factors describes the measured apparent relative dielectric permittivity for axially varying materials; variations in the transverse plane are described by an inverse averaging model with nonuniform spatial weighting. We define the sensitivity of a TDR probe as the change in the measured travel time for a given change in the average soil water content for rods of a fixed length. For rods with dielectric coatings, this sensitivity increases with the dielectric permittivity of the coating and the rod radius and decreases with the soil dielectric permittivity. Due to the dependence of the sensitivity on the soil water content, coated rods will not measure the actual average water content for conditions of axially variable water contents.

Original languageEnglish (US)
Pages (from-to)271-279
Number of pages9
JournalWater Resources Research
Volume32
Issue number2
DOIs
StatePublished - Feb 1996
Externally publishedYes

Fingerprint

time domain reflectometry
permittivity
Water content
coatings
coating
water content
probe
Permittivity
Coatings
soil water content
Soils
soil water
travel
travel time
Travel time
Waveguides
soil

ASJC Scopus subject areas

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

Cite this

Spatial averaging of water content by time domain reflectometry : Implications for twin rod probes with and without dielectric coatings. / Ferre, Paul A; Rudolph, D. L.; Kachanoski, R. G.

In: Water Resources Research, Vol. 32, No. 2, 02.1996, p. 271-279.

Research output: Contribution to journalArticle

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