Web page of Sébastien Beyou

Background and Position

I received a Bachelor degree in mathematics in 2007 and a Master in mathematical modeling and scientific computing in 2009 at University of Rennes I.

I was a PhD student at INRIA under the supervision of Étienne Mémin and François Le Gland.

Research areas

The topic of my PhD thesis is the estimation of the velocity fields of oceanic currents given satellite images; the approach chosen is a stochastic framework with Ensemble Kalman Filter, particles filters, and data assimilation techniques.

Thesis summary

This thesis applies fluid flows estimation with particle filtering-based assimilation methods imaged using digital cameras. We rely on a specific particle filter, of which the proposal distribution is given by an Ensemble Kalman Filter, namely the Weighted Ensemble Kalman Filter. Two variations of this method are introduced and tested. The first consists in using a dynamical noise (which modelizes the model uncertainty and separates the particles from each others); its spatial form obeys to a power law stemming from the phenomenological theory of the turbulence. The second variation relies on a multiscale assimilation scheme introducing successive refinements from observations at smaller and smaller scales. These two methods are tested on synthetic and experimental sequences of 2D incompressible flows. Results show an important gain on the Root Mean Square Error. They are then tested on real satellite images; here a good temporal coherence and a good tracking of vortex structures are observed. The multiscale assimilation shows a visible gain on the number of reconstructed scales. Some additional variations are also presented and tested in order to take into account important problems in a real satellite context, like the management of missing data areas in the Sea Surface Temperature sequence. Lastly an experiment involving a Weighted Ensemble Kalman Filter with a complete oceanic model is presented for a surface currents fields assimilation in Iroise Sea near the English Channel mouth.

Publication list (with postscript or pdf files if available)