A TDR array probe for monitoring near-surface soil moisture distribution

Sheng, Wenyi; Zhou, Rong; Sadeghi, Morteza; Babaeian, Ebrahim; Robinson, David A.; Tuller, Markus; Jones, Scott B.. 2017 A TDR array probe for monitoring near-surface soil moisture distribution. Vadose Zone Journal, 16 (4), vzj2016.11.0112. 8, pp.

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Near-surface soil conditions (i.e., moisture and temperature) moderate mass and energy exchange at the soil–atmosphere interface. While remote sensing offers an effective means for mapping near-surface moisture content across large areas, in situ measurements, targeting those specific remotely sensed soil depths, are poorly understood and high-resolution near-surface measurement capabilities are lacking. Time domain reflectometry (TDR) is a well-established, accurate measurement method for soil dielectric permittivity and moisture content. A TDR array was designed to provide centimeter-resolution measurements of near-surface soil moisture. The array consists of nine stainless steel TDR rods spaced 1 cm apart, acting as waveguide pairs to form eight two-rod TDR probes in series. A critical aspect of the design was matching the spacing of the coaxial cable–TDR rod transition to avoid unwanted reflections in the waveforms. The accuracy of the TDR array permittivity measurement (±1 permittivity unit) was similar to that of conventional TDR as verified in dielectric liquids. Electric field numerical simulations showed minimal influence of adjacent rods during a given rod-pair measurement. The evaporation rate determined by the TDR array compared well with mass balance data in a laboratory test. Near-surface soil moisture profile dynamics were monitored at centimeter-depth resolution using the TDR array in a field experiment where volumetric moisture content estimates (0–8 cm) were within 2% of conventional three-rod TDR probes averaging across 0 to 8 cm and from 1- to 3-cm depths

Item Type: Publication - Article
Digital Object Identifier (DOI):
CEH Sections/Science Areas: Emmett
ISSN: 1539-1663
NORA Subject Terms: Agriculture and Soil Science
Date made live: 14 Jun 2017 11:22 +0 (UTC)

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