Abstract. In atmospheric chemistry retrievals and data assimilation systems, observation errors associated with satellite radiances are chosen empirically and generally treated as uncorrelated. In this work, we estimate inter-channel error covariances for the Infrared Atmospheric Sounding Interferometer (IASI) and evaluate their impact on ozone assimilation with the chemical transport model MOCAGE (MOdèle de Chime Atmospheric à Grand Echelle). The method used to calculate observation errors is a diagnostic based on the observation and analysis residual statistics already adopted in numerical weather prediction centers. We used a subset of 280 channels covering the spectral range between 980 and 1100 cm⁻¹ to estimate the observation error covariance matrix. We computed hourly 3D-Var analyses and compared the resulting O₃ fields against ozonesondes and the measurements provided by the Microwave Limb Sounder (MLS). The results show significant differences between using the estimated error covariance matrix with respect to the empirical diagonal matrix employed in previous studies. The validation of the analyses against independent data reports a significant improvement especially in the tropical stratosphere. The computational cost has also been reduced when the estimated covariance is employed in the assimilation system.

中文翻译：

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IASI辐射误差协方差矩阵的估计及其对臭氧分析的影响

摘要。在大气化学检索和数据同化系统中，凭经验选择与卫星辐射相关的观测误差，通常将其视为不相关。在这项工作中，我们估算了红外大气探测干涉仪（IASI）的通道间误差协方差，并使用化学传输模型MOCAGE（MOdèlede Chime AtmosphericàGrand Echelle）评估了其对臭氧吸收的影响。用于计算观测误差的方法是一种基于数值天气预报中心已经采用的观测和分析残差统计信息的诊断方法。我们使用了280个通道的子集，覆盖了980至1100 cm ^-1之间的光谱范围估计观察误差协方差矩阵。我们计算了每小时的3D-Var分析，并将产生的O ₃场与臭氧探空仪以及由微波测深仪（MLS）提供的测量结果进行了比较。结果表明，相对于先前研究中使用的经验对角矩阵，使用估计的误差协方差矩阵存在显着差异。根据独立数据进行的分析验证表明，特别是在热带平流层中，该方法已有显着改善。当在同化系统中采用估计的协方差时，也减少了计算成本。