Estimating surface CO2 fluxes from space-borne CO2 dry air mole fraction observations using an ensemble Kalman Filter
Estimating surface CO2 fluxes from space-borne CO2 dry air mole fraction observations using an ensemble Kalman Filter
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DOI：
10.5194/acpd-8-19917-2008
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
L. Feng;P. Palmer;H. Bösch;S. Dance
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文献类型：
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作者：
L. Feng;P. Palmer;H. Bösch;S. Dance
为了准备NASA轨道碳观测站(OCO)的数据，我们开发了一个集合卡尔曼滤波(EnKF)，用于从星载CO2干空气摩尔分数观测(XCO2)估计8天的区域地表CO2通量，并使用一系列合成实验对该方法进行评估。OCO的32天占空比每16天在短波红外波长的反向散射太阳辐射的最低点和闪烁测量之间交替。EnKF使用一个状态集合来表示误差协方差，以估计144个地理区域的8天CO2地表通量。我们使用12×8天的滞后窗口，认识到X二氧化碳测量包括来自先前时间窗口的地表通量信息。将地表二氧化碳通量与XCO2的大气分布联系起来的观测算子包括：a)将地表通量与全球二氧化碳浓度三维分布联系起来的GEOS-Chem输送模式，在无云且具有气溶胶光学厚度的OCO测量的时间和地点进行采样；以及b)与场景有关的平均核函数，它将二氧化碳剖面与XCO2联系在一起，说明了最低点和闪烁测量之间的差异，以及相关的场景相关观测误差。结果表明，OCO-XCO2测量显著降低了地表CO2通量估算的不确定性。通常情况下，闪烁测量在约束海洋二氧化碳通量估计方面更好。陆地热带地区的XCO2测量结果全年都很稀少，要么是因为云，要么是因为烟雾。闪烁测量通过对邻近海洋上新的大陆外流进行精确采样，为估计热带陆地二氧化碳通量提供了最有效的约束。我们还给出了敏感性实验的结果，这些实验研究了通量估计如何随1)偏差和对应关系而变化：L·冯(lfan@Staffmail.ed.ac.uk)无偏误差，2)替代占空比，3)测量密度和相关性，4)估计通量估计的空间分辨率，以及5)减小滞后窗口的长度和集合的大小。在本手稿的修改阶段，OCO仪器在2009年2月24日发射后未能进入轨道。本文提出的EnKF公式也适用于GOSAT对二氧化碳和甲烷的测量。
We have developed an ensemble Kalman Filter (EnKF) to estimate 8-day regional surface fluxes of CO 2 from space-borne CO 2 dry-air mole fraction observations (XCO2) and evaluate the approach using a series of synthetic experiments, in preparation for data from the NASA Orbiting Carbon Observatory (OCO). The 32-day duty cycle of OCO alternates every 16 days between nadir and glint measurements of backscattered solar radiation at short-wave infrared wavelengths. The EnKF uses an ensemble of states to represent the error covariances to estimate 8-day CO 2 surface fluxes over 144 geographical regions. We use a 12 ×8-day lag window, recognising that X CO2 measurements include surface flux information from prior time windows. The observation operator that relates surface CO 2 fluxes to atmospheric distributions of XCO2 includes: a) the GEOS-Chem transport model that relates surface fluxes to global 3-D distributions of CO2 concentrations, which are sampled at the time and location of OCO measurements that are cloud-free and have aerosol optical depths <0.3; and b) scene-dependent averaging kernels that relate the CO 2 profiles to XCO2, accounting for differences between nadir and glint measurements, and the associated scene-dependent observation errors. We show that OCO XCO2 measurements significantly reduce the uncertainties of surface CO 2 flux estimates. Glint measurements are generally better at constraining ocean CO 2 flux estimates. Nadir XCO2 measurements over the terrestrial tropics are sparse throughout the year because of either clouds or smoke. Glint measurements provide the most effective constraint for estimating tropical terrestrial CO 2 fluxes by accurately sampling fresh continental outflow over neighbouring oceans. We also present results from sensitivity experiments that investigate how flux estimates change with 1) bias and Correspondence to: L. Feng (lfeng@staffmail.ed.ac.uk) unbiased errors, 2) alternative duty cycles, 3) measurement density and correlations, 4) the spatial resolution of estimated flux estimates, and 5) reducing the length of the lag window and the size of the ensemble. At the revision stage of this manuscript, the OCO instrument failed to reach its orbit after it was launched on 24 February 2009. The EnKF formulation presented here is also applicable to GOSAT measurements of CO2 and CH4.