Correction of TDR-based soil water content measurements in conductive soils
Correction of TDR-based soil water content measurements in conductive soils
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DOI：
10.1016/j.geoderma.2007.10.022
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发表时间：
2008-01
期刊：
影响因子：
6.1
通讯作者：
M. Bittelli;F. Salvatorelli;P. Pisa
中科院分区：
文献类型：
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作者：
M. Bittelli;F. Salvatorelli;P. Pisa
时间域反射仪(TDR)是一种广泛应用的土壤水分测量技术。使用时间域反射仪(TDR)的主要假设是损耗可以忽略不计，因此假设只有实部确定TDR测量的视介电常数值。这一假设不适用于表面导电的土壤(粘性土壤)或土壤溶液中存在高浓度电解质的土壤(盐渍土壤)，因为在这些条件下，虚部的贡献变得重要。介质损耗对TDR测量的主要影响之一是高估了SWC。在这项研究中，我们提出了一种从视介电常数测量中分离实部和虚部的方法。这种方法可以通过使用TDR测量的电导率作为介质损耗的指标来修正SWC高估。采用烘干重量法作为一种独立的土壤水分评价方法。最初的SWC高估(相对于基于烘干重量法的测量)达到了土壤总饱和度的20%，经过校正后，差异减小到3-5%。该方法可以仅基于测量的介电常数和电导率的知识来应用，因此它很容易适用于现场实验。
Time Domain Reflectometry (TDR) is a widespread technique for measurement of soil water content (SWC). The main assumption behind the use of Time Domain Reflectometry (TDR) is of negligible losses, therefore assuming that only the real part determines the value of the TDR-measured apparent dielectric permittivity. This assumption does not hold for soils where surfaces are conductive (clay soils) or where high concentrations of electrolyte are present in the soil solution (saline soils) because under these conditions the contribution of the imaginary part becomes important. One of the main effects of dielectric losses on the TDR measurement is overestimation of SWC. In this study we present a methodology for separating the real and the imaginary part from the measurement of the apparent dielectric permittivity. This approach allows correction of the SWC overestimation, by using the TDR-measured electrical conductivity as indicator of dielectric losses. Oven-dry gravimetric soil water content was used as an independent method for soil water content assessment. The original SWC overestimation (in respect to the oven-dry gravimetric based measurement) reached values of up to 20% of total soil saturation, after the correction the differences were reduced to a 3–5%. The methodology can be applied based on knowledge of measured permittivity and electrical conductivity only, making it readily applicable to field experiments.