Accuracies of field CO2–H2O data from open-path eddy-covariance flux systems: assessment based on atmospheric physics and biological environment

IF 1.8 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Geoscientific Instrumentation Methods and Data Systems Pub Date : 2022-10-21 DOI:10.5194/gi-11-335-2022
Xinhua Zhou, Tian Gao, Ning Zheng, Bai Yang, Yanlei Li, Fengyuan Yu, Tala Awada, Jiaojun Zhu
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Abstract

Ecosystem CO2–H2O data measured by infrared gas analyzers in open-path eddy-covariance (OPEC) systems have numerous applications, such as estimations of CO2 and H2O fluxes in the atmospheric boundary layer. To assess the applicability of the data for these estimations, data uncertainties from analyzer measurements are needed. The uncertainties are sourced from the analyzers in zero drift, gain drift, cross-sensitivity, and precision variability. These four uncertainty sources are individually specified for analyzer performance, but so far no methodology exists yet to combine these individual sources into a composite uncertainty for the specification of an overall accuracy, which is ultimately needed. Using the methodology for closed-path eddy-covariance systems, this overall accuracy for OPEC systems is determined from all individual uncertainties via an accuracy model and further formulated into CO2 and H2O accuracy equations. Based on atmospheric physics and the biological environment, for EC150 infrared CO2–H2O analyzers, these equations are used to evaluate CO2 accuracy (±1.22 mgCO2 m−3, relatively ±0.19 %) and H2O accuracy (±0.10 gH2O m−3, relatively ±0.18 % in saturated air at 35 C and 101.325 kPa). Both accuracies are applied to conceptual models addressing their roles in uncertainty analyses for CO2 and H2O fluxes. For the high-frequency air temperature derived from H2O density along with sonic temperature and atmospheric pressure, the role of H2O accuracy in its uncertainty is similarly addressed. Among the four uncertainty sources, cross-sensitivity and precision variability are minor, although unavoidable, uncertainties, whereas zero drift and gain drift are major uncertainties but are minimizable via corresponding zero and span procedures during field maintenance. The accuracy equations provide rationales to assess and guide the procedures. For the atmospheric background CO2 concentration, CO2 zero and CO2 span procedures can narrow the CO2 accuracy range by 40 %, from ±1.22 to ±0.72 mgCO2 m−3. In hot and humid weather, H2O gain drift potentially adds more to the H2O measurement uncertainty, which requires more attention. If H2O zero and H2O span procedures can be performed practically from 5 to 35 C, the H2O accuracy can be improved by at least 30 %: from ±0.10 to ±0.07 gH2O m−3. Under freezing conditions, the H2O span procedure is impractical but can be neglected because of its trivial contributions to the overall uncertainty. However, the zero procedure for H2O, along with CO2, is imperative as an operational and efficient option under these conditions to minimize H2O measurement uncertainty.
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开放路径涡旋-协方差通量系统野外CO2-H2O数据的准确性:基于大气物理和生物环境的评估
开放路径涡旋协方差(OPEC)系统中红外气体分析仪测量的生态系统CO2 - H2O数据有许多应用,例如大气边界层中CO2和H2O通量的估计。为了评估这些估计的数据的适用性,需要从分析仪测量的数据不确定度。不确定性来自于分析仪的零漂移、增益漂移、交叉灵敏度和精度变异性。这四个不确定度源是为分析仪性能单独指定的,但到目前为止还没有方法将这些单独的不确定度源组合成一个综合的不确定度,以规范总体精度,这是最终需要的。使用封闭路径涡流协方差系统的方法,欧佩克系统的总体精度通过精度模型从所有个体不确定性中确定,并进一步制定为二氧化碳和h2o精度方程。基于大气物理和生物环境,对EC150红外CO2 - H2O分析仪,使用这些方程来评估CO2精度(±1.22 mgCO2 m - 3,相对±0.19%)和H2O精度(±0.10 gH2O m - 3,相对±0.18%,在35°C和101.325 kPa的饱和空气中)。这两种精度都适用于概念模型,解决了它们在CO2和h2o通量不确定性分析中的作用。对于由H2O密度、声波温度和大气压力导出的高频空气温度,H2O精度在其不确定性中的作用也同样得到了解决。在四个不确定性来源中,交叉灵敏度和精度变化是次要的,虽然不可避免,不确定性,而零漂移和增益漂移是主要的不确定性,但在现场维护期间通过相应的零和跨度程序可以最小化。准确度方程为评估和指导程序提供了依据。对于大气背景CO2浓度,CO2零和CO2跨度程序可以将CO2精度范围缩小40%,从±1.22到±0.72 mgCO2 m - 3。在炎热潮湿的天气中,H2Ogain漂移可能会增加H2O测量的不确定度,需要引起更多的注意。如果能在5到35°C范围内实际进行H2O零点和H2O跨度测量,H2O精度至少可以提高30%:从±0.10到±0.07 gH2O m - 3。在冻结条件下,水跨度过程是不切实际的,但可以忽略,因为它对总体不确定性的贡献微不足道。然而,在这些条件下,H2O和CO2的零程序作为一种操作和有效的选择是必要的,以最大限度地减少H2O测量的不确定性。
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来源期刊
Geoscientific Instrumentation Methods and Data Systems
Geoscientific Instrumentation Methods and Data Systems GEOSCIENCES, MULTIDISCIPLINARYMETEOROLOGY-METEOROLOGY & ATMOSPHERIC SCIENCES
CiteScore
3.70
自引率
0.00%
发文量
23
审稿时长
37 weeks
期刊介绍: Geoscientific Instrumentation, Methods and Data Systems (GI) is an open-access interdisciplinary electronic journal for swift publication of original articles and short communications in the area of geoscientific instruments. It covers three main areas: (i) atmospheric and geospace sciences, (ii) earth science, and (iii) ocean science. A unique feature of the journal is the emphasis on synergy between science and technology that facilitates advances in GI. These advances include but are not limited to the following: concepts, design, and description of instrumentation and data systems; retrieval techniques of scientific products from measurements; calibration and data quality assessment; uncertainty in measurements; newly developed and planned research platforms and community instrumentation capabilities; major national and international field campaigns and observational research programs; new observational strategies to address societal needs in areas such as monitoring climate change and preventing natural disasters; networking of instruments for enhancing high temporal and spatial resolution of observations. GI has an innovative two-stage publication process involving the scientific discussion forum Geoscientific Instrumentation, Methods and Data Systems Discussions (GID), which has been designed to do the following: foster scientific discussion; maximize the effectiveness and transparency of scientific quality assurance; enable rapid publication; make scientific publications freely accessible.
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