A Markov chain model for characterizing medium heterogeneity and sediment layering structure
A Markov chain model for characterizing medium heterogeneity and sediment layering structure
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DOI：
10.1029/2008wr006924
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发表时间：
2008-09
影响因子：
5.4
通讯作者：
M. Ye;R. Khaleel
中科院分区：
文献类型：
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作者：
M. Ye;R. Khaleel
通过利用“软”数据（例如，初始含水量θi），将基于转移概率的马尔可夫链模型应用于沉积物结构分类，以表征介质的非均匀性和沉积物的分层结构。TP/MC方法进行评估，通过模拟包气带水分运动在现场，地层由不完全分层的土层。土壤异质性是通过土壤质地类别的几何空间变异性来表征的。当携带介质非均质性和地层学特征的θi测量值不包括在TP/MC模型中时，不可能识别水平TP。θi测量值在转换为土壤类别时，对于绘制现场普遍存在的土壤分层结构是必要的。确定性地对待每一个土壤类的土壤水力参数，并估计芯样的基础上。为了评估表征土壤类别几何形状的不确定性，生成土壤类别的多个条件实现。蒙特卡罗模拟表明，模拟的平均含水量符合相应的现场观测。在夹在两个细纹理层之间的粗砂层中观察到的水分羽流的分裂，在再分布期间羽流的东南向运动，以及底部细层下方的近零流体通量都得到了充分的模拟。通过Monte Carlo模拟计算的95%置信区间充分捕获了现场测量含水量的空间变异性。调查数据调理对模拟结果的影响表明，减少调理数据并不一定会恶化模拟结果，如果其他调理数据存在的平均长度内的土壤类。TP/MC方法是灵活的，使得其他类型的站点表征数据（例如，地球物理数据）可以在它们变得可用时被并入。
By leveraging use of “soft” data (e.g., initial moisture content, θi), this study applies the transition probability (TP) based Markov chain (MC) model to sediment textural classes for characterizing the medium heterogeneity and sediment layering structure. The TP/MC method is evaluated by simulating the vadose zone moisture movement at a field site, where the stratigraphy consists of imperfectly stratified soil layers. Soil heterogeneity is characterized via spatial variability of the geometry of soil textural classes. When the θi measurements, which carry signature about medium heterogeneity and stratigraphy, are not included in the TP/MC model, it is not possible to identify the horizontal TP. The θi measurements, when transformed into soil classes, are necessary in mapping the soil layering structure prevalent at the site. The soil hydraulic parameters for each soil class are treated deterministically and are estimated on the basis of core samples. To evaluate uncertainty in characterizing geometry of the soil classes, multiple conditional realizations of the soil classes are generated. A Monte Carlo simulation shows that the simulated mean moisture contents agree well with corresponding field observations. The observed splitting of the moisture plume in a coarse sand layer that is sandwiched between two fine‐textured layers, the southeastward movement of the plume during the redistribution period, and the near‐zero fluid flux below the bottom fine layer are adequately simulated. Spatial variability of the field‐measured moisture content is sufficiently captured by the 95% confidence intervals calculated from the Monte Carlo simulations. Investigating the effect of data conditioning on the simulated results shows that a reduction of conditioning data does not necessarily deteriorate simulation results if other conditioning data exist within the mean length of the soil classes. The TP/MC method is flexible so that other types of site characterization data (e.g., geophysical data) can be incorporated as they become available.