Developments in operational shelf sea modelling in Danish waters

An initial implementation of an operational system for the Danish waters ha s been carried out. The system consists of an observational network of wate r level stations, a two-dimensional model that computes simultaneously area s with different grid resolution, and a sequential data assimilation method . For assimilation of water level measurements an approximate Kalman filter algorithm, the ensemble Kalman filter, has been implemented. The ensemble Kalman filter has a computational cost much lower than the cost associated with a full Kalman filter application, and therefore it is suitable to be a pplied in an operational system. The error covariance matrix in this specif ic case tends to a quasi-steady state after a few days of assimilation. Thu s, a Kalman filter with a constant weighting matrix has been applied during a 13-day test period to assimilate observed water levels in a model coveri ng the entire North Sea and Baltic Sea area. The corrections achieved by th e assimilation procedure are significant in most of the validation stations . Moreover, the error estimation provided by the filter is very accurate, e specially in the inner Danish waters. (C) 2001 Academic Press.