Xinhua Zhou, Tian Gao, Ning Zheng, Bai Yang, Yanlei Li, Fengyuan Yu, Tala Awada, Jiaojun Zhu
{"title":"Accuracies of field CO2–H2O data from open-path eddy-covariance flux systems: assessment based on atmospheric physics and biological environment","authors":"Xinhua Zhou, Tian Gao, Ning Zheng, Bai Yang, Yanlei Li, Fengyuan Yu, Tala Awada, Jiaojun Zhu","doi":"10.5194/gi-11-335-2022","DOIUrl":null,"url":null,"abstract":"Ecosystem CO<span><sub>2</sub></span>–H<span><sub>2</sub></span>O data measured by infrared\ngas analyzers in open-path eddy-covariance (OPEC) systems have numerous\napplications, such as estimations of CO<span><sub>2</sub></span> and H<span><sub>2</sub></span>O fluxes in the\natmospheric boundary layer. To assess the applicability of the data for\nthese estimations, data uncertainties from analyzer measurements are needed.\nThe uncertainties are sourced from the analyzers in zero drift, gain drift,\ncross-sensitivity, and precision variability. These four uncertainty sources\nare individually specified for analyzer performance, but so far no methodology\nexists yet to combine these individual sources into a composite uncertainty\nfor the specification of an overall accuracy, which is ultimately needed.\nUsing the methodology for closed-path eddy-covariance systems, this overall\naccuracy for OPEC systems is determined from all individual uncertainties\nvia an accuracy model and further formulated into CO<span><sub>2</sub></span> and H<span><sub>2</sub></span>O\naccuracy equations. Based on atmospheric physics and the biological\nenvironment, for EC150 infrared CO<span><sub>2</sub></span>–H<span><sub>2</sub></span>O analyzers, these\nequations are used to evaluate CO<span><sub>2</sub></span> accuracy (<span>±1.22</span> mgCO<span><sub>2</sub></span> m<span><sup>−3</sup></span>, relatively <span>±0.19</span> %) and H<span><sub>2</sub></span>O accuracy (<span>±0.10</span> gH<span><sub>2</sub></span>O m<span><sup>−3</sup></span>, relatively <span>±0.18</span> % in saturated air at 35 <span><sup>∘</sup></span>C and 101.325 kPa). Both accuracies are applied to conceptual\nmodels addressing their roles in uncertainty analyses for CO<span><sub>2</sub></span> and\nH<span><sub>2</sub></span>O fluxes. For the high-frequency air temperature derived from\nH<span><sub>2</sub></span>O density along with sonic temperature and atmospheric pressure, the\nrole of H<span><sub>2</sub></span>O accuracy in its uncertainty is similarly addressed. Among\nthe four uncertainty sources, cross-sensitivity and precision variability\nare minor, although unavoidable, uncertainties, whereas zero drift and gain\ndrift are major uncertainties but are minimizable via corresponding zero and\nspan procedures during field maintenance. The accuracy equations provide\nrationales to assess and guide the procedures. For the atmospheric\nbackground CO<span><sub>2</sub></span> concentration, CO<span><sub>2</sub></span> zero and CO<span><sub>2</sub></span> span\nprocedures can narrow the CO<span><sub>2</sub></span> accuracy range by 40 %, from <span>±1.22</span> to <span>±0.72</span> mgCO<span><sub>2</sub></span> m<span><sup>−3</sup></span>. In hot and humid weather, H<span><sub>2</sub></span>O\ngain drift potentially adds more to the H<span><sub>2</sub></span>O measurement uncertainty,\nwhich requires more attention. If H<span><sub>2</sub></span>O zero and H<span><sub>2</sub></span>O span procedures\ncan be performed practically from 5 to 35 <span><sup>∘</sup></span>C, the H<span><sub>2</sub></span>O\naccuracy can be improved by at least 30 %: from <span>±0.10</span> to <span>±0.07</span> gH<span><sub>2</sub></span>O m<span><sup>−3</sup></span>. Under freezing conditions, the H<span><sub>2</sub></span>O span\nprocedure is impractical but can be neglected because of its trivial\ncontributions to the overall uncertainty. However, the zero procedure for\nH<span><sub>2</sub></span>O, along with CO<span><sub>2</sub></span>, is imperative as an operational and efficient\noption under these conditions to minimize H<span><sub>2</sub></span>O measurement uncertainty.","PeriodicalId":48742,"journal":{"name":"Geoscientific Instrumentation Methods and Data Systems","volume":null,"pages":null},"PeriodicalIF":1.8000,"publicationDate":"2022-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Geoscientific Instrumentation Methods and Data Systems","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.5194/gi-11-335-2022","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
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.
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.