Flux measurements over heterogeneous surfaces with growing vegetation and a limited fetch are a difficult task, as measurement heights that are too high or too low above the canopy adversely affect results. The aim of this study is to assess implications from measurement height in regard to low-pass filtering, footprint representativeness, and energy balance closure for a clear-cut site with regrowing vegetation of varying height. For this, measurements from two open-path eddy-covariance systems at different heights are compared over the course of one growing season. Particular attention is paid to low-pass-filtering corrections, for which five different methods are compared. Results indicate significant differences between fluxes from the upper and lower systems, which likely result from footprint differences and an insufficient spectral correction for the lower system. Different low-pass-filtering corrections add an uncertainty of 3.4% (7.0%) to CO₂ fluxes and 1.4% (3.0%) to H₂O fluxes for the upper (lower) system, also leading to considerable differences in cumulative fluxes. Despite limitations in the analysis, which include the difficulty of applying a footprint model at this study site and the likely influence of advection on the total exchange, the analysis confirms that information about the choice of spectral correction method and measurement-height changes are critical for interpreting data at complex sites.

在植被生长和获取有限的异质表面上进行通量测量是一项艰巨的任务，因为在树冠之上太高或太低的测量高度会对结果产生不利影响。本研究的目的是评估测量高度对低通滤波、足迹代表性和能量平衡闭合的影响，用于具有不同高度再生植被的清晰场地。为此，在一个生长季节的过程中比较了来自不同高度的两个开放路径涡度协方差系统的测量值。特别注意低通滤波校正，比较了五种不同的方法。结果表明来自上层和下层系统的通量之间存在显着差异，这可能是由于足迹差异和较低系统的光谱校正不足造成的。不同的低通滤波校正给 CO 增加了 3.4% (7.0%) 的不确定性₂通量和 1.4% (3.0%) 到上（下）系统的 H ₂ O 通量，也导致累积通量的相当大的差异。尽管分析存在局限性，包括在该研究地点应用足迹模型的困难以及平流对总交换的可能影响，但分析证实，有关光谱校正方法选择和测量高度变化的信息对于解释复杂站点的数据。