Building the COllaborative Carbon Column Observing Network (COCCON): long-term stability and ensemble performance of the EM27/SUN Fourier transform spectrometer
Building the COllaborative Carbon Column Observing Network (COCCON): long-term stability and ensemble performance of the EM27/SUN Fourier transform spectrometer
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DOI：
10.5194/amt-12-1513-2019
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发表时间：
2019-03-11
影响因子：
3.8
通讯作者：
Orphal, Johannes
中科院分区：
文献类型：
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作者：
Frey, Matthias;Sha, Mahesh K.;Orphal, Johannes
在一项长达3.5年的研究中，用于温室气体观测的移动式太阳能吸收布鲁克EM27/SUN光谱仪的长期性能与位于同一位置的参考布鲁克IFS 125HR光谱仪进行了对比，后者是总碳柱观测网络（TCCON）的一部分。我们发现EM27/SUN在几年的时间尺度上是稳定的；EM27/SUN与官方TCCON产品之间每年的漂移为XCO2为0.02 ppmv， XCH4为0.9 ppbv，在比较的1西格玛精度范围内，XCO2为0.6 ppmv， XCH4为4.3 ppbv。两个数据集之间的偏差对于XCO2为3.9 ppmv，对于XCH4为13.0 ppbv。为了避免与灵敏度相关的伪影，EM27/SUN还与来自全分辨率TCCON干涉图的截断IFS 125HR数据集进行了比较。XCO2的漂移为0.02 ppmv /年，XCH4的漂移为0.2 ppbv /年，XCO2和XCH4的1西格玛精度分别为0.4 ppmv和1.4 ppbv。两个数据集之间的偏差对于XCO2为0.6 ppmv，对于XCH4为0.5 ppbv。EM27/SUN具有长期的稳定性，可以作为现有偏远地区TCCON网络的有益补充。为了达到一致的性能，这种扩展需要通过应用共同的质量保证措施对涉及的任何光谱仪进行仔细的测试。协同碳柱观测网络（COCCON）基础设施的一个主要目标是为所有EM27/SUN运营商提供这些服务。在COCCON开发的框架内，测试了30个EM27/SUN光谱仪的性能，发现非常均匀，在部署之前在卡尔斯鲁厄理工学院进行的集中检查增强了性能。考虑到每个光谱仪测量的仪器线形参数，相对于XCO2长期研究中使用的参考EM27/SUN，整个系集的平均偏差为0.20 ppmv，而XCH4的平均偏差为0.8 ppbv。XCO2的平均标准差为0.13 ppmv， XCH4的平均标准差为0.6 ppbv。除了基于绝对差的稳健度量外，我们还计算了经验校准因子之间的标准差。得到的2西格玛不确定度为XCO2为0.6 ppmv， XCH4为2.2 ppbv。正如在一个设备上进行的长期研究所表明的那样，可以假设每个单独仪器的剩余经验校准因子随着时间的推移是恒定的。因此，这些经验因子的应用有望进一步提高EM27/SUN网络的一致性，超越上述经验校正因子之间的分散。
In a 3.5-year long study, the long-term performance of a mobile, solar absorption Bruker EM27/SUN spectrometer, used for greenhouse gas observations, is checked with respect to a co-located reference Bruker IFS 125HR spectrometer, which is part of the Total Carbon Column Observing Network (TCCON). We find that the EM27/SUN is stable on timescales of several years; the drift per year between the EM27/SUN and the official TCCON product is 0.02 ppmv for XCO2 and 0.9 ppbv for XCH4, which is within the 1 sigma precision of the comparison, 0.6 ppmv for XCO2 and 4.3 ppbv for XCH4. The bias between the two data sets is 3.9 ppmv for XCO2 and 13.0 ppbv for XCH4. In order to avoid sensitivity-dependent artifacts, the EM27/SUN is also compared to a truncated IFS 125HR data set derived from full-resolution TCCON interferograms. The drift is 0.02 ppmv for XCO2 and 0.2 ppbv for XCH4 per year, with 1 sigma precisions of 0.4 ppmv for XCO2 and 1.4 ppbv for XCH4, respectively. The bias between the two data sets is 0.6 ppmv for XCO2 and 0.5 ppbv for XCH4. With the presented long-term stability, the EM27/SUN qualifies as an useful supplement to the existing TCCON network in remote areas. To achieve consistent performance, such an extension requires careful testing of any spectrometers involved by application of common quality assurance measures. One major aim of the COllaborative Carbon Column Observing Network (COCCON) infrastructure is to provide these services to all EM27/SUN operators. In the framework of COCCON development, the performance of an ensemble of 30 EM27/SUN spectrometers was tested and found to be very uniform, enhanced by the centralized inspection performed at the Karlsruhe Institute of Technology prior to deployment. Taking into account measured instrumental line shape parameters for each spectrometer, the resulting average bias across the ensemble with respect to the reference EM27/SUN used in the long-term study in XCO2 is 0.20 ppmv, while it is 0.8 ppbv for XCH4. The average standard deviation of the ensemble is 0.13 ppmv for XCO2 and 0.6 ppbv for XCH4. In addition to the robust metric based on absolute differences, we calculate the standard deviation among the empirical calibration factors. The resulting 2 sigma uncertainty is 0.6 ppmv for XCO2 and 2.2 ppbv for XCH4. As indicated by the executed long-term study on one device presented here, the remaining empirical calibration factor deduced for each individual instrument can be assumed constant over time. Therefore the application of these empirical factors is expected to further improve the EM27/SUN network conformity beyond the scatter among the empirical calibration factors reported above.