Wang Xing Chang, Wang Chuan Kuan
Center for Ecological Research, Northeast Forestry University, Harbin 150040, China.
Ying Yong Sheng Tai Xue Bao. 2016 Sep;27(9):2779-2788. doi: 10.13287/j.1001-9332.201609.012.
Coordinate rotation is an essential step in eddy covariance (EC) flux measurements particularly on complex terrains. Systematically assessing impacts of coordinate rotation methods can improve the accuracy in EC flux estimations. Taking the Maoershan flux tower in a temperate deci-duous forest on valley slopes as a case, we comprehensively examined the effects of various tilt-correction methods on sensible heat flux (H), latent heat flux (LE), CO fluxes (F), energy ba-lance, friction velocity (u), and vertical velocity (w) using the standardized major axis method. Compared with the unrotated fluxes, the double rotation (DR), planar fit (PF), vertical velocity unbiased planar fit (NBPF), monthly planar fit (MPF), triple rotation (TR) and monthly sector-wist planar fit (MSWPF) changed the H by +1.5%, +3.8%, +3.1%, +3.3%, -1.3% and -7.1%, respectively. The NBPF and DR increased LE by 1.0% and 0.4%, respectively. The PF also increased LE by 0.671 W·m, and the MPF decreased LE by 0.4%, but increased the intercept by 0.747 W·m. In contrast, the MSWPF and TR decreased the LE by 4.5% and 15.1%, respectively. The coordinate rotation reduced the F by 6.0% (DR)-12.1% (TR). Among the studied methods, the PF increased the energy balance closure by about 2%, whereas the TR decreased it by about 6%. In the light of u and w, the TR and NBPF were inappropriate for anemometer tilt correction. Considering the precision and practical application of EC measurements, we recommend the PF as the first choice for the Maoershan flux tower site, followed by the DR. These findings are useful for tilt correction of anemometer in EC flux observations over complex terrains.
坐标旋转是涡度相关（EC）通量测量中的关键步骤，特别是在复杂地形上。系统地评估坐标旋转方法的影响可以提高EC通量估算的准确性。以位于山谷坡地温带落叶林中的帽儿山通量塔为例，我们使用标准化主轴方法全面研究了各种倾斜校正方法对感热通量（H）、潜热通量（LE）、CO通量（F）、能量平衡、摩擦速度（u）和垂直速度（w）的影响。与未旋转的通量相比，双旋转（DR）、平面拟合法（PF）、垂直速度无偏平面拟合法（NBPF）、月度平面拟合法（MPF）、三旋转（TR）和月度扇形加权平面拟合法（MSWPF）对H的改变分别为+1.5%、+3.8%、+3.1%、+3.3%、-1.3%和-7.1%。NBPF和DR分别使LE增加了1.0%和0.4%。PF也使LE增加了0.671 W·m，而MPF使LE降低了0.4%，但截距增加了0.747 W·m。相比之下，MSWPF和TR分别使LE降低了4.5%和15.1%。坐标旋转使F降低了6.0%（DR）至12.1%（TR）。在所研究的方法中，PF使能量平衡闭合度提高了约2%，而TR使其降低了约6%。就u和w而言，TR和NBPF不适用于风速仪倾斜校正。考虑到EC测量的精度和实际应用，我们建议帽儿山通量塔站点首选PF，其次是DR。这些发现对于复杂地形上EC通量观测中风速仪的倾斜校正具有参考价值。
