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Laboratory evaluation of time domain reflectometry for continuous monitoring of stream stage, channel profile, and aqueous conductivity
Author(s) -
Tidwell Vincent C.,
Brainard James R.
Publication year - 2005
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2004wr003416
Subject(s) - reflectometry , transmission line , classification of discontinuities , time domain , conductivity , materials science , dielectric , attenuation , dispersion (optics) , acoustics , remote sensing , environmental science , geology , optics , telecommunications , computer science , optoelectronics , physics , mathematical analysis , mathematics , quantum mechanics , computer vision
Time domain reflectometry (TDR) operates by propagating a radar frequency electromagnetic pulse down a transmission line while monitoring the reflected signal. As the electromagnetic pulse propagates along the transmission line, it is subject to impedance by the dielectric properties of the media along the transmission line (e.g., air, water, and sediment), reflection at dielectric discontinuities (e.g., air‐water or water‐sediment interface), and attenuation by electrically conductive materials (e.g., salts and clays). Taken together, these characteristics provide a basis for integrated stream monitoring, specifically, concurrent measurement of stream stage, channel profile, and aqueous conductivity. Requisite for such application is a means of extracting the desired stream parameters from measured TDR traces. Analysis is complicated by the fact that interface location and aqueous conductivity vary concurrently and multiple interfaces may be present at any time. For this reason a physically based multisection model employing the S 11 scatter function and Debeye parameters for dielectric dispersion and loss is used to analyze acquired TDR traces. Here we explore the capability of this multisection modeling approach for interpreting TDR data acquired from complex environments, such as encountered in stream monitoring. A series of laboratory tank experiments was performed in which the depth of water, depth of sediment, and conductivity were varied systematically. Comparisons between modeled and independently measured data indicate that TDR measurements can be made with an accuracy of ±3.4 × 10 −3 m for sensing the location of an air‐water or water‐sediment interface and ±7.4% of actual for the aqueous conductivity.