  Online data assimilation in time series models over a large spatial extent is
an important problem in both geosciences and robotics. Such models are
intrinsically high-dimensional, rendering traditional particle filter
algorithms ineffective. Though methods that begin to address this problem
exist, they either rely on additional assumptions or lead to error that is
spatially inhomogeneous. I present a novel particle-based algorithm for online
approximation of the filtering problem on such models, using the fact that each
locus affects only nearby loci at the next time step. The algorithm is based on
a Metropolis-Hastings-like MCMC for creating hybrid particles at each step. I
show simulation results that suggest the error of this algorithm is uniform in
both space and time, with a lower bias, though higher variance, as compared to
a previously-proposed algorithm.
