Complete Data Fusionof GOME-2 and IASI Ozone Profiles: State of the Art and Comparison with In-Situ Measurements and Synergistic Retrievals

Remote sensing observations of the composition of Earth's atmosphere are performed with instruments operating on space-borne and airborne platforms and from ground-based stations. In this context, vertical profiles of atmospheric variables are usually derived with an inversion procedure (retrieval) from the observed radiances. When one or more instruments observe the same portion of the atmosphere, the information obtained from the different measurements can be combined to obtain a unique vertical profile of improved quality compared to the profiles retrieved from the single observations. Synergistic retrieval is the most comprehensive way to combine different measurements of the same quantity. However, a method called Complete Data Fusion was proposed that, in linear approximation conditions, provides products equivalent to synergistic retrieval with simpler implementation requirements. Here, we present the results of applying the Complete Data Fusion method to measurements of vertical profiles performed by IASI and GOME-2. The method's inputs are the profiles retrieved from IASI and from GOME-2 measurements characterized by their a priori information, covariance matrices and averaging kernel matrices. The output consists of a single profile characterized by a-priori information, covariance matrix, and averaging kernel matrix. Two kinds of analysis have been performed in this work, both based on publicly available datasets. The first kind refers to the in-situ measurements sites of Uccle and De Bilt and to all the IASI and GOME2 measurements available in a fixed spatial-temporal interval centered on the considered in-situ measurement. In this case, the quality of the fused profile is compared with the quality of the original profiles retrieved from IASI and GOME-2 measurements in terms of errors and number of degrees of freedom. The original and the fused measurements are also compared in terms of differences from the in-situ measurements. The second kind of analysis refers to cases in which in-situ measurements, MetOp-B IASI and GOME-2 measurements and synergistic retrieval are available. In this case, the fusion results are compared with the two original standalone retrievals and the synergistic retrieval in terms of errors, number of degrees of freedom, and differences from the corresponding in-situ measurement. The discussion of these two cases, based on publicly available observational data, will also focus on the CDF method's critical issues and its state of development.