Data assimilation activities: 1. Provide NCEO and the NERC community with accessible core models equipped for data assimilation which can be used for Earth System Science investigations and Observing System Simulation Experiments. 2. Interrogate UK Earth System components and derive data-consistent global state and model parameter estimates for initialisation and driving of models. 3. Investigate new techniques that will enable DA to meet the science challenges of tomorrow, including work with the Met Office and other meteorological forecast centres to ensure NCEO DA work has impact and to promote critical mass in key research and development areas.