In this study we perform a reanalysis of the sparse MEA CRRES relativistic electron data using a relatively simple one-dimensional radial diffusion model and a Kalman filtering approach. By combining observations with the model in an optimal way we produce a high time and space resolution reanalysis of the radiation belt electron fluxes over a 50-d period starting on 18 August 1990. The results of the reanalysis clearly show pronounced peaks in the electron phase space density (PSD), which can not be explained by the variations in the outer boundary, and can only be produced by a local acceleration processes. The location of the innovation vector shows that local acceleration is most efficient at L* = 5.5 for electrons at K = 0.11 G0.5 R E and mu = 700 MeV/G. Sensitivity numerical experiments for various values of mu and K indicate that peaks in PSD become stronger with increasing K and mu. To verify that our results are not affected by the limitations of the satellite orbit and coverage, we performed an ``identical twin'' experiments with synthetic data specified only at the locations for which CRRES observations are available. Our results indicate that the model with data assimilation can accurately reproduce the underlying structure of the PSD even when data is sparse. The identical twin experiments also indicate that PSD at a particular L-shell is determined by the local processes and cannot be accurately estimated unless local measurements are available.