Developments in Operational Shelf Sea Modelling in Danish Waters

Abstract

An initial implementation of an operational system for the Danish waters has been carried out. The system consists of an observational network of water level stations, a two-dimensional model that computes simultaneously areas 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 applied in an operational system. The error covariance matrix in this specific case tends to a quasi-steady state after a few days of assimilation. Thus, 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 covering the entire North Sea and Baltic Sea area. The corrections achieved by the assimilation procedure are significant in most of the validation stations. Moreover, the error estimation provided by the filter is very accurate, especially in the inner Danish waters.