From 1992 to 2001 he worked at the Met Office in the U.K., where he developed the linear and adjoint models used in their four-dimensional variational data assimilation system. He gained his PhD while working at the Met Office, before moving to the University of Reading in 2001. His scientific interest is in the mathematics of data assimilation, in particular the development and analysis of efficient numerical methods to solve the data assimilation problem in large, complex systems. His recent projects have included work on coupled atmosphere-ocean data assimilation, land surface data assimilation and the representation of observation error correlations. He is part of the UK National Centre for Earth Observation (NCEO).