Ensemble perturbations in Data Assimilation

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For data assimilation schemes relying on ensemble methods, uncertain aspect of the model have to be perturbed within the range of their uncertainty. Different methods for the generation of perturbations can be used based on unperturbed time serie:

  • EOF modes: EOF are computed based on the unperturbed field and perturbations are random linear combination of the EOFs with a given temporal correlation.
  • Fourier modes: see paper:

A. Barth, A. Alvera-Azcárate, J.-M. Beckers, J. Staneva, E. V. Stanev, and J. Schulz-Stellenfleth. Correcting surface winds by assimilating High-Frequency Radar surface currents in the German Bight. Ocean Dynmics, 61(5):599–610, 2011. doi: 10.1007/s10236-010-0369-0. URL http://hdl.handle.net/2268/83330. Preprint

The code is available here http://modb.oce.ulg.ac.be/mediawiki/upload/Alex/Perturbations/pert_fft_trans2.m.

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