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The 8 February 2019 at 14h00

PhD Defense: Oliver GUILLET – “Modelling spatially correlated observation errors in varational data assimilation on unstructured meshes”

Brigitte Yzel |  Salle JCA, Cerfacs, Toulouse |  

In this thesis, we propose a class of methods to represent spatial observation error correlations numerically in variational data assimilation. Based on the existing link between solutions of the time-implicit diffusion equation and Matérn correlation functions, we design correlation operators and inverse correlation operators that are appropriate for large datasets. Discretizing the diffusion equation with the finite element method allows us to account for data that do not necessarily lie on a structured mesh, as is the case with satellite observations assimilated in meteorology. Experiments are carried out using data from the infrared imager Seviri, the images of which are known for containing strong horizontal correlations. We show that the quality of our correlation model may depend locally on the spatial distribution of the observations. Nevertheless, by introducing an auxiliary mesh to perform the finite element computations, we can control this dependency to a large extent. Improving the accuracy of the method this way comes at the expense of making the inverse correlation operator more complicated. Finally, strategies for efficiently modelling the inverse of the correlation operator are proposed.

Jury :

Anthony Weaver           (Cerfacs)                                      Advisor
Michel Yann                  (Météo-France)                            Co Advisor
Marcin Chrust               (ECMWF, UK)                              Examiner
Selime Gürol                (Cerfacs)                                      Examiner
Serge Gratton              (INPT-IRIT)                                   Examiner
Marc Bocquet              (Ecole des Ponts Paris Tech)       Rapporteur
Emmanuel Cosme       (Université Grenoble Alpes)        Rapporteur
Arthur Vidard               (INRIA)                                         Rapporteur
Xavier Vasseur            (ISAE-Supaero)                           Invited member

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The video presentation of the NextSim project has just been released : CERFACS is involved in the NextSim project (). The primary objective is to increase the capabilities of Computational Fluid Dynamics tools on extreme-scale parallel computing platforms for aeronautical design. This project has received funding from the European High-Performance Computing Joint Undertaking (JU) under grant agreement N° 956104. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and Spain, France, Germany. This project has received funding from the Agence Nationale de la Recherche (ANR) under grant agreement N° ANR-20-EHPC-0002-02. For more information, please visit Read more

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