OPTIMAL ESTIMATION OF PARAMETERS FOR A 2-DIMENSIONAL HYDRODYNAMICAL MODEL OF THE ARABIAN GULF

The parameters of a two-dimensional numerical tidal model of the Arabi an Gulf are estimated by optimal assimilation of data from tide gauges at several of the Saudi Aramco tide stations. The parameters estimate d am the bottom drag coefficient and a correction to the bathymetry an d are in general allowed to be position dependent. Significant improve ments in the predictions of the model are obtained. The method used is based on the minimization of a cost function measuring the difference between the observed and computed water heights at the tide stations, the gradient of the cost function being computed by the adjoint metho d. The parameter functions are approximated by piecewise constant or p iecewise linear approximations, and the cost function is minimized usi ng the quasi-Newton algorithm CONMIN. It is found in general that in o rder to obtain stable estimates, it is necessary to include in the cos t function a term that penalizes large variations in the parameter fun ctions. Techniques are developed to reduce the storage demands of the algorithm sufficiently to permit the assimilation of 29 days of tidal data.