“…More broadly speaking, the exploration of alternative proposal densities in the context of data assimilation has started only recently. See, for example, Vanden-Eijnden and Weare (2012), Morzfeld, Tu, Atkins and Chorin (2012), Van Leeuwen (2015), Llopis, Kantas, Beskos and Jasra (2018), and van Leeuwen, Künsch, Nerger, Potthast and Reich (2018). filtering Figure 3: The the initial PDF π 0 , the forecast PDF π 1 , the filtering PDF π 1 , and the smoothing PDF π 0 for a simple Gaussian transition kernel.…”