Accuracy of the cosmic-ray soil water content probe in humid forest ecosystems: The worst case scenario
Accuracy of the cosmic-ray soil water content probe in humid forest ecosystems: The worst case scenario
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DOI：
10.1002/wrcr.20463
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发表时间：
2013-09-01
影响因子：
5.4
通讯作者：
Vereecken, H.
中科院分区：
文献类型：
--
作者：
Bogena, H. R.;Huisman, J. A.;Vereecken, H.
土壤含水量是土壤-植被-大气连续体的关键状态变量之一，它在土壤表面的水分和能量交换中起着重要作用。在野外或小流域尺度上测量整体土壤含水量的新方法是宇宙射线探针（CRP）。最近对CRP测量的研究主要来自位于非常干燥地区的试验点和沙质土壤的农田。在本研究中，利用无线传感器网络（SoilNet）的分布式连续土壤含水量测量数据，研究了CRP测量在湿润森林生态系统中土壤含水量测定中的准确性。由于凋落物层的存在，这种生态系统对CRP的应用不太有利。此外，土壤有机质和地下生物量的晶格水和碳水化合物降低了传感器的有效深度，因此在CRP的校准中被考虑在内。生物质中的氢降低了中子计数率水平，从而降低了宇宙射线探测器的灵敏度，从而增加了测量的不确定度。这种不确定性通过使用较长的集成时间（例如，24小时）得到补偿。在未明确考虑凋落物层的情况下，宇宙射线探测器能够评估整体土壤水分动态，RMSE约为0.03 cm(3)/cm(3)。通过将凋落物层模拟含水量纳入校准，可以获得更好的精度。
Soil water content is one of the key state variables in the soil-vegetation-atmosphere continuum due to its important role in the exchange of water and energy at the soil surface. A new promising method to measure integral soil water content at the field or small catchment scale is the cosmic-ray probe (CRP). Recent studies of CRP measurements have mainly presented results from test sites located in very dry areas and from agricultural fields with sandy soils. In this study, distributed continuous soil water content measurements from a wireless sensor network (SoilNet) were used to investigate the accuracy of CRP measurements for soil water content determination in a humid forest ecosystem. Such ecosystems are less favorable for CRP applications due to the presence of a litter layer. In addition, lattice water and carbohydrates of soil organic matter and belowground biomass reduce the effective sensor depth and thus were accounted for in the calibration of the CRP. The hydrogen located in the biomass decreased the level of neutron count rates and thus also decreased the sensitivity of the cosmic-ray probe, which in turn resulted in an increase of the measurement uncertainty. This uncertainty was compensated by using longer integration times (e.g., 24 h). For the Wustebach forest site, the cosmic-ray probe enabled the assessment of integral daily soil water content dynamics with a RMSE of about 0.03 cm(3)/cm(3) without explicitly considering the litter layer. By including simulated water contents of the litter layer in the calibration, a better accuracy could be achieved.