基于涡度相关技术估算植被/大气间净CO2交换量中的不确定性

近年来，涡度相关技术的进步使陆地生态系统CO2通量的长期和连续观测成为可能。目前，涡度相关技术是全球通量观测网络（FLUXNET）测定植被/大气间CO2通量的主要技术手段，但绝大部分CO2通量观测站点都处于非典型的理想条件下，不能完全满足涡度相关技术的基本假设条件，从而导致基于涡度相关技术估算植被/大气间净生态系统CO2交换量的不确定性。系统介绍了涡度相关技术的基本假设，基本理论公式和误差的类型与特征等理论问题，重点阐述了通量测定中仪器本身的物理限制、二维和三维的气流运动、数据处理的方法和夜间通量的低估等不确定性的主要来源，并据此对通量观测研究中需要优先考虑的问题提出一些建议。研究认为数据质量控制与分析以及误差评价是不同通量站点间的结果比较和全球尺度综合分析的过程中需重点考虑的问题。

UNCERTAINTIES IN LONG-TERM STUDIES OF NET ECOSYSTEM CO2 EXCHANGE WITH THE ATMOSPHERE BASED ON EDDY COVARIANCE TECHNIQUE

Direct and continuous long-term measurements of canopy-scale carbon dioxide fluxes have only recently become possible due to the improvement of eddy covariance technique. Now it has been widely used in long-term observation studies of CO_2 uptake and release by terrestrial ecosystem. A global network of micrometeorological tower sites (FLUXNET) uses eddy covariance methods to measure the exchanges of CO_2 between terrestrial ecosystem and atmosphere, but a majority of the site are not in ideal conditions, which can not fully meet the basic assumption of eddy covariance technique for the CO_2 flux measurement, thus resulting in some uncertainties in the flux measurement. Chinese Terrestrial Ecosystem Flux Observational Research Network (ChinaFLUX) has been established, which relies on Chinese Ecosystem Research Network (CERN) and applies eddy covariance of microclimatology as main research method to study fluxes of carbon dioxide between the vegetation and soil of typical ecosystem and atmosphere. The objective of this paper is to introduce the basic assumption of the eddy covariance technique, the basic theoretical equations, the types and characteristics of errors in long-term measurements and to elucidate emphatically the uncertainties in the flux measurement due to physical limitation of instrumentation, two and three dimensional air flow motion effects, methods of data processing, and underestimation of nighttime fluxes, etc. Where possible, this paper makes recommendations concerning methodologies and research priorities. Without some understanding of and ability to compensate for these uncertainties, cross-site comparisons and global scale synthesis are difficult and uncertain at best. Thus, dada quality analysis and control (QA/QC) and errors assessments are necessary for cross-site comparisons and global scale synthesis.