The dielectric calibration of capacitance probes for soil hydrology using an oscillation frequency response model
The dielectric calibration of capacitance probes for soil hydrology using an oscillation frequency response model
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DOI：
10.5194/hess-2-111-1998
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发表时间：
1998-03-01
影响因子：
6.3
通讯作者：
Bell, JP
中科院分区：
文献类型：
--
作者：
Robinson, DA;Gardner, CMK;Bell, JP
电容探针是一种快速、安全且相对便宜的测量土壤相对介电常数的方法，可用于估计土壤含水量。电容探头的初始实验使用仪器的频率响应和土壤含水量之间的经验校准。这的缺点是校准取决于仪器。本文介绍了一种双重校准策略;仪器频率转换为相对介电常数（介电常数），然后可以针对土壤含水量进行校准。该方法的优点是可以实现从土壤介电常数到土壤含水量的二次标定，与仪器无关，并可以与时域反射法等其他介电方法进行比较。该模型，这是从电路分析，预测，成功地，在不同的相对电阻率的液体中的仪器的频率响应，仅使用在空气和水中的测量。该方法已成功地用于10个表面电容探针和1个深度电容探针的标定。研究结果表明，仪器电极的几何特性是模型中的一个重要参数，其值可以通过测量来确定。土壤表观介电常数与体积含水量之间的关系在过去30年中一直是许多研究的主题。两条线的调查已经开发，时域反射计（TDR）和电容。这两种方法都声称测量相对介电常数，因此应该是可比的。本文证明了IH电容探头高估了相对介电常数！因为介质的离子电导率增加。导电离子溶液被用来测试这种影响的大小上的相对介电常数的测定。响应建模，使相对介电常数，独立于离子电导率，可以确定在溶液中的电导率高达0.25 S m（1）。结果发现，溶液EC小于0.05 S m（-1）的介电常数的影响不大。测量.
Capacitance probes are a fast, safe and relatively inexpensive means of measuring the relative permittivity of soils, which can then be used to estimate soil water content. Initial experiments with capacitance probes used empirical calibrations between the frequency response of the instrument and soil water content. This has the disadvantage that the calibrations are instrument-dependent. A twofold calibration strategy is described in this paper; the instrument frequency is turned into relative permittivity (dielectric constant) which can then be calibrated against soil water content. This approach offers the advantages of making the second calibration, from soil permittivity to soil water content, instrument-independent and allows comparison with other dielectric methods, such as time domain reflectometry.A physically based model, used to calibrate capacitance probes in terms of relative permittivity (epsilon(r)) is presented. The model, which was developed from circuit analysis, predicts, successfully, the frequency response of the instrument in liquids with different relative permittivities, using only measurements in air and water. It was used successfully to calibrate 10 prototype surface capacitance insertion probes (SCIPs) and a depth capacitance probe. The findings demonstrate that the geometric properties of the instrument electrodes were an important parameter in the model, the value of which could be fixed through measurement.The relationship between apparent soil permittivity and volumetric water content has been the subject of much research in the last 30 years. Two lines of investigation have developed, time domain reflectometry (TDR) and capacitance. Both methods claim to measure relative permittivity and should therefore be comparable. This paper demonstrates that the IH capacitance probe overestimates relative permittivity! as the ionic conductivity of the medium increases. Electrically conducting ionic solutions a ere used to test the magnitude of this effect on the determination of relative permittivity. The response was modelled so that the relative permittivity, independent of ionic conductivity, could be determined in solutions with an electrical conductivity of up to 0.25 S m(1). It was found that a solution EC of less than 0.05 S m(-1) had little impact on the permittivity. measurement.