Direct 4D-Var assimilation of all-sky radiances. Part I: Implementation Bauer, Peter ; Geer, Alan J. ; Lopez, Philippe ; Salmond, Deborah Abstract Publication: Quarterly Journal of the Royal Meteorological Society Pub Date: October 2010 DOI: 10.1002/qj.659 Bibcode: 2010QJRMS.136.1868B