Assimilation of Doppler radar current data into numerical ocean models

A technique is presented for the assimilation of ocean surface currents determined from Doppler radar systems into numerical ocean models. An approach is taken in which the Doppler radar current data act as if there were an additional layer of water overlying the ocean surface. A pseudo-shearing stress resulting from the difference between the model-predicted velocity and the Doppler radar velocity is added to that of the wind in order to force a model. Test applications are presented for an ocean model of the Monterey Bay, California, region. Comparisons are made between optimized and non-optimized assimilation techniques based on the shearing stress approach. The optimized assimilation scheme provides the minimum additional shearing stress while achieving a significant nudging of the model surface currents toward the basic characteristics of the observed field of Doppler radar currents. Analyses indicate that the model surface currents take on the general pattern of the Doppler radar currents but not always the magnitude. The radar currents are shown to have significant divergences and unrealistic spatial variations of divergence. Characteristics of this sort for oppler data suggest additional processing for such observations. (C) 1998 Elsevier Science Ltd. All rights reserved.