Parameter Estimation Analysis of the Evaporation Method for Determining Soil Hydraulic Properties
Parameter Estimation Analysis of the Evaporation Method for Determining Soil Hydraulic Properties
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DOI：
10.2136/sssaj1998.03615995006200040007x
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发表时间：
1998-07
影响因子：
2.9
通讯作者：
J. Šimůnek;M. Genuchten;O. Wendroth
中科院分区：
文献类型：
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作者：
J. Šimůnek;M. Genuchten;O. Wendroth
土壤水力特性是影响变饱和土壤水流运动的重要参数。我们用参数估计法和修正的Wind法对实验室蒸发实验的水力性质进行了估算。该参数估计方法结合了Richards方程的一维数值解和MarQuardt-Levenberg优化方案。在我们的研究中，我们使用了数值生成的数据和实验室测量的数据。在含有两种不同土壤的10厘米高的土芯上进行了两次试验。岩芯内部的压力头是用五个张力计测量的，而顶部的蒸发水分损失是通过称重土壤样本来确定的。参数估计分析的目标函数是根据岩心最终总水量和一个或几个张力计的压力水头读数确定的。对数值生成数据的分析表明，优化方法对形状因子(N)和饱和含水率(θS)最敏感，对残余含水率(θr)最不敏感。在靠近土壤表面测量的压头被发现比在较低位置测量的压头对参数估计技术更有价值。优化后的水力参数与Wind分析得到的水力参数吻合较好。在测得的压头范围内(0~-700 cm)，所有优化措施对土壤水力性质的影响结果基本一致。超出这一范围的外推涉及很高的不确定性，因为参数θ、r和n之间高度相关。
Soil hydraulic properties are important parameters affecting water flow in variably saturated soils. We estimated the hydraulic properties from a laboratory evaporation experiment using both a parameter estimation method and the modified Wind method. The parameter estimation method combined a one-dimensional numerical solution of the Richards equation with the Marquardt-Levenberg optimization scheme. In our study we used both numerically generated data and data measured in the laboratory. Two experiments were carried out on 10-cm-high soil cores containing two different soils. Pressure heads inside the cores were measured with five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The objective function for the parameter estimation analysis was defined in terms of the final total water volume in the core and pressure head readings by one or several tensiometers. An analysis of numerically generated data showed that the optimization method was most sensitive to the shape factor (n) and the saturated water content (θ s ) and least to the residual water content (θ r ). Pressure heads measured close to the soil surface were found to be more valuable for the parameter estimation technique than those measured at lower locations. The optimized hydraulic parameters corresponded closely with those obtained using Wind's analysis. All optimizations gave similar results for the soil hydraulic properties within the range of measured pressure heads (0 to -700 cm). Extrapolation beyond this range involved a high level of uncertainty because of high correlation between parameters θ r and n.