Intercomparison of Methods for the Simultaneous Estimation of Zero-Plane Displacement and Aerodynamic Roughness Length from Single-Level Eddy-Covariance Data
Intercomparison of Methods for the Simultaneous Estimation of Zero-Plane Displacement and Aerodynamic Roughness Length from Single-Level Eddy-Covariance Data
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DOI：
10.1007/s10546-013-9905-z
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发表时间：
2014-01
影响因子：
4.3
通讯作者：
A. Graf;A. Boer;A. Moene;H. Vereecken
中科院分区：
文献类型：
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作者：
A. Graf;A. Boer;A. Moene;H. Vereecken
我们应用三种方法从单层涡动协方差数据中通过气动测量高度(与地面以上的测量高度)和气动粗糙度长度来估计零面位移。两种方法(一种是迭代方法，另一种是基于回归的方法)是基于对数风廓线中的泛函，得到了固有的同时估计两种风速的方法。第三种方法是基于通量-方差相似性，其中估计和连续估计是独立的步骤。每种方法又被进一步分为两种方法，它们在解决方法(剖面方法)或变量(分别是垂直风和温度的方差)方面不同。所有的方法都被应用于在一块生长着的大麦田上空进行测量，在那里，统一的冠层高度及其频繁的监测为由此产生的时变因子估计提供了可信的限度。在对每种方法应用了说明其有效条件范围(例如稳定性)的特定数据过滤之后，六种方法中的五种能够描述与作物生长和收获相关的粗糙度参数的时间变化，其中四种方法在大多数情况下在0.3米内达成一致。将同样的方法应用于由完全生长的甜菜和相邻收获的田地的不同贡献组成的更不同的足迹的测量，显示出粗糙度参数对甜菜比例的可信的依赖关系。它还表明，产生最大异常值的方法可能因场地条件和稳定性而不同。因此，我们得出的结论是，当从单层测量中确定具有未知属性的树冠时，重要的是比较多种方法的结果，而不是依赖于单一方法。结果的集合平均值或中位数，可能在消除产生异常值的方法之后，有助于产生更稳健的估计。估计几乎完全是物理上可信的，尽管被认为是未知的，并与上述方法和结果同时估计。
We applied three approaches to estimate the zero-plane displacementthrough the aerodynamic measurement height(withandbeing the measurement height above the surface), and the aerodynamic roughness length, from single-level eddy covariance data. Two approaches (one iterative and one regression-based) were based on the universal function in the logarithmic wind profile and yielded an inherently simultaneous estimation of bothand. The third approach was based on flux–variance similarity, where estimation ofand consecutive estimation ofare independent steps. Each approach was further divided into two methods differing either with respect to the solution technique (profile approaches) or with respect to the variable (variance of vertical wind and temperature, respectively). All methods were applied to measurements above a large, growing wheat field where a uniform canopy height and its frequent monitoring provided plausibility limits for the resulting estimates of time-variantand. After applying, for each approach, a specific data filtering that accounted for the range of conditions (e.g. stability) for which it is valid, five of the six methods were able to describe the temporal changes of roughness parameters associated with crop growth and harvest, and four of them agreed onto within 0.3 m most of the time. Application of the same methods to measurements with a more heterogeneous footprint consisting of fully-grown sugarbeet and a varying contribution of adjacent harvested fields exhibited a plausible dependence of the roughness parameters on the sugarbeet fraction. It also revealed that the methods producing the largest outliers can differ between site conditions and stability. We therefore conclude that when determiningfor canopies with unknown properties from single-level measurements, as is increasingly done, it is important to compare the results of a number of methods rather than rely on a single one. An ensemble average or median of the results, possibly after elimination of methods that produce outliers, can help to yield more robust estimates. The estimates ofwere almost exclusively physically plausible, althoughwas considered unknown and estimated simultaneously with the methods and results described above.