北京325米气象塔上CO_2梯度观测数据质量控制与评价

Data Processing and Quality Assessment of the Eddy Covariance System of the 325-m Meteorology Tower in Beijing

近些年涡度相关系统在城市通量研究中得到了广泛应用,因城市下垫面的特殊性和复杂性,以及系统观测原理和仪器精度存在着局限性,使得结果存在10%以上偏差,故必须对原始观测数据进行质量控制和评价。本文对北京325 m气象塔七层高度上的CO_2(二氧化碳)、能量等通量进行了长期观测,研究了涡度相关技术在城市环境通量观测中的适用性,设计出了一套适合于复杂城市下垫面上的涡度相关系统资料前处理和质量控制方案,并对比了不同修正方案效果。分析结果表明,城市下垫面环境中计算CO_2通量的最优周期为30 min;二次坐标旋转法优于平面拟合法;频率响应修正后的感热通量提高5.21%,潜热通量和CO_2通量均提高9.42%。空气密度脉动修正Liu法(Liu,2005)优于WPL法(Webb et al.,1980);湍流谱在惯性副区满足-2/3次方定律,协方差谱满足-4/3次方定律。经过这套前处理和质量控制方案,原始数据中有79%能够用于基础研究,该质量控制与评价体系可为复杂城市下垫面通量研究提供参考。

Advances in instrumentation, notably the eddy covariance（EC） technique, offer a tool for the direct measurement of representative flux data in urban areas. The complexity of the urban underlying surface and limitations of the EC system cause the obtained surface fluxes to not be true values. If no correction is applied, the error will be greater than 10%. The applicability of the EC technique, quality assessment of the EC system, and processing of its data, in urban Beijing, were analyzed using the CO2 flux data and energy measured at seven levels of the 325-m meteorology tower in the city. Analysis of the data from the tower showed that the best time period to calculate the CO2 flux for the urban underlying surface is 30 minutes. The secondary coordinate rotation method is superior to plane fitting. After frequency response correction, the sensible heat flux increased by 5.21%, and the latent heat flux and CO2 flux were increased by 9.42%. Liu＇s method（Liu, 2005） was found to be better than the Webb E K, Pearman G I, and Leuning R＇s（WPL） method（Webb et al., 1980） in the air density pulse correction step. The turbulent spectral checks of the data quality evaluation were satisfactory. After rigorous data screening, the final result showed that approximately 79% of the flux data were good.