Time domain reflectometry measurement principles and applications

TLDR

Time‑domain reflectometry (TDR) is a highly accurate, automatable technique for measuring porous‑media water content and electrical conductivity, but its dielectric‑based calibration must account for clay and organic matter, and recent advances promise cheaper, more precise tools and additional property measurements. TDR determines water content from dielectric permittivity and conductivity from signal attenuation, using empirical and dielectric mixing models, with probe configurations tailored to specific sites and media. © 2002 John Wiley & Sons, Ltd.

Abstract

Abstract Time domain reflectometry (TDR) is a highly accurate and automatable method for determination of porous media water content and electrical conductivity. Water content is inferred from the dielectric permittivity of the medium, whereas electrical conductivity is inferred from TDR signal attenuation. Empirical and dielectric mixing models are used to relate water content to measured dielectric permittivity. Clay and organic matter bind substantial amounts of water, such that measured bulk dielectric constant is reduced and the relationship with total water content requires individual calibration. A variety of TDR probe configurations provide users with site‐ and media‐specific options. Advances in TDR technology and in other dielectric methods offer the promise not only for less expensive and more accurate tools for electrical determination of water and solute contents, but also a host of other properties such as specific surface area, and retention properties of porous media. Copyright © 2002 John Wiley & Sons, Ltd.