Fusion d'observation altimétriques satellitaires par assimilation de données : préparation de la mission SWOT

par Florian Le Guillou

Projet de thèse en Océan, Atmosphère, Hydrologie

Sous la direction de Emmanuel Cosme.

Thèses en préparation à Grenoble Alpes , dans le cadre de École doctorale terre, univers, environnement (Grenoble) , en partenariat avec Institut des Géosciences de l'Environnement (laboratoire) depuis le 01-11-2018 .


  • Résumé

    Les cartes actuelles de topographie de surface de l'océan, indispensables pour de nombreuses applications climatiques, sont actuellement conçues en interpolant linéairement, en temps et en espace, les observations altimétriques satellitaires. Pour la mission altimétrique de nouvelle génération SWOT, prévue pour lancement en 2021, ce procédé sera certainement insuffisant. L'objectif de cette thèse est de développer une méthodologie permettant d'introduire de la dynamique océanique dans le processus d'interpolation, basée sur de l'assimilation de données.

  • Titre traduit

    Merging satellite altimetry observations by data assimilation: preparation of the SWOT mission


  • Résumé

    Future SWOT altimetric observations could revolutionize our understanding of oceanic turbulent processes, from which the sub-mesoscale (kilometric scales) plays an essential role in the dissipation of kinetic energy and the exchange of properties between the surface ocean and the deep ocean. For example, the knowledge of the current velocity field and its gradients will make it possible to estimate the mixing rates that control the energy cascades between the different scales. These potentialities will be realized if we can infer maps of small scale currents velocity and their gradients from SWOT observations of ocean surface topography. Maps of ocean surface topography and current have been produced for nearly 20 years by the AVISO consortium as part of the DUACS project (Figure 2). The DUACS system, unique worldwide, processes the available satellite altimetry data to produce these maps. This processing is based in particular on a statistical interpolation of existing data, in space and time. Given the density of these data distributed along linear traces, the spatial resolution of 1/4° obtained from these maps does not allow the resolution of dynamic scales below 200 km. In 2021, the next-generation SWOT (Surface Water and Ocean Topography, NASA/CNES) altimetry mission will be launched, which will provide SSH images at a kilometric resolution, possibly resolving dynamics to a scale of 10 to 50 km. SWOT could thus pave the way for the development of maps of ocean surface topography, current velocity and velocity gradients at a resolution allowing the study of sub-mesoscale processes. But the inversion method by statistical interpolation implemented in the current DUACS system will most certainly be insufficient to process these data efficiently. The PhD is part of a project to develop the DUACS system in order to make it capable of processing SWOT data as efficiently as possible, by explicitly introducing information on ocean dynamics, in the form of data assimilation with a simple model, for example of the quasi-geostrophic type.