Fine-wire thermometer to correct CO2 fluxes by open-path analyzers for artificial density fluctuations
Fine-wire thermometer to correct CO2 fluxes by open-path analyzers for artificial density fluctuations
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DOI：
10.1016/j.agrformet.2007.06.007
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发表时间：
2007-11-12
影响因子：
6.2
通讯作者：
Burba, George
中科院分区：
文献类型：
--
作者：
Grelle, Achim;Burba, George
细导线温度计被施加到测量高频空气温度波动的平均长度的光路的LI-7500开路气体分析仪，用于CO2通量测量在瑞典的森林砍伐。由细线温度数据导出的热通量用于校正光路内密度波动的CO2通量。由于该方法结合了传统Webb-Pearman-Leuning项中的自然热通量和分析仪表面加热引起的热通量，它提供了一种手段，以最大限度地减少或消除可能导致生态系统在淡季期间明显的CO吸收的开路通量的偏差，以及对其他时期碳损失的普遍低估。所提出的技术进行了比较，其他两种方法：传统的WPL校正和理论校正的仪器表面加热与经验估计的仪器表面温度。所有方法均参考闭合路径LI-6262系统，因为该系统中的高频温度波动被长进气管衰减。测量结果表明，细线校正产生的积分通量在4%以内的LI-6262衍生通量。经验估计温度的理论校正导致积分通量在使用LI-6262测量的通量的6%以内。在同一时期，传统的WPL校正低估了CO，损失19%。在另一个时期与外部加热施加到LI-7500，传统的WPL校正导致低估的CO2排放量的66%，而PRT校正产生的流量在8%的LI-6262。实验证实，开路CO2通量测量的偏差主要是由仪器表面加热引起的，这种热量应该在密度校正中考虑。实验还表明，细导线温度计为开路加热现象提供了可靠的仪器解决方案，即使在开路分析仪上施加外部热量时，也可以每半小时和每季度进行适当的校正。(C)2007 Elsevier B. V.保留所有权利。
A fine-wire thermometer was applied to measure high-frequency air temperature fluctuations averaged over the length of the optical path of an LI-7500 open-path gas analyzer that was used for CO2 flux Measurements over a forest clear-cut in Sweden. Heat fluxes derived by the fine-wire temperature data were used to correct the CO2 fluxes for density fluctuations within the optical path. As this method incorporates both natural heat fluxes, accounted for in the conventional Webb-Pearman-Leuning term, and heat fluxes caused by analyzer surface heating, it provides a means to minimize or eliminate the bias in open-path fluxes that could lead to apparent CO-uptake in ecosystems during the off-season period, and to a general underestimation of carbon losses in other periods. The proposed technique was compared to two other methods: the conventional WPL-correction and a theoretical correction for the instrument surface heating with empirically estimated instrument surface temperatures. All methods were referenced to a closed-path LI-6262 system because high frequency temperature fluctuations in that system were attenuated by the long intake tube. Measurements demonstrated that the fine-wire correction yielded integrated fluxes that were within 4% of the LI-6262-derived fluxes. The theoretical correction with empirically estimated temperatures led to integrated fluxes being within 6% of those measured using the LI-6262. For the same time period, the conventional WPL-correction underestimated CO, losses by 19%. During another period with external heating applied to the LI-7500, the conventional WPL-correction led to an underestimation of the CO2 efflux by 66%, while the PRT-correction yielded fluxes within 8% of the LI-6262. The experiment confirmed that the bias in the open-path CO2 flux measurements is mostly caused by instrument surface heating, and that such heat should be accounted for in the density corrections. The experiment also demonstrated that a fine-wire thermometer provided a reliable instrumental solution for the open-path heating phenomenon, and could give adequate corrections on a half-hourly and seasonal basis even when external heat was applied to the open-path analyzer. (C) 2007 Elsevier B.V. All rights reserved.