A hybrid ensemble transform filter for nonlinear and spatially extended dynamical systems
For researchers in data assimilation, this hybrid filter offers a practical way to leverage the strengths of both Kalman and particle filters, though the improvement is incremental.
The authors propose a hybrid ensemble transform filter that adaptively combines ensemble Kalman and particle filters for nonlinear and spatially extended dynamical systems. Numerical experiments show improved performance over both filters at moderate ensemble sizes.
Data assimilation is the task to combine evolution models and observational data in order to produce reliable predictions. In this paper, we focus on ensemble-based recursive data assimilation problems. Our main contribution is a hybrid filter that allows one to adaptively bridge between ensemble Kalman and particle filters. While ensemble Kalman filters are robust and applicable to strongly nonlinear systems even with small and moderate ensemble sizes, particle filters are asymptotically consistent in the large ensemble size limit. We demonstrate numerically that our hybrid approach can improve the performance of both Kalman and particle filters at moderate ensemble sizes. We also show how to implement the concept of localization into a hybrid filter, which is key to its applicability to spatially extended systems.