Some Practical Ways to Determine Coastal Current´s Vertical Structure

Remote sensing technology has made it possible to rapidly observe wide areas of the ocean surface. To determine subsurface conditions from these observations requires the application of hydrodynamic principles. For coastal currents, the viscous dynamics can be applied to efficiently project surface data downward to obtain the current´s vertical structure in real time. This method has been developed for use with remotely sensed surface current data obtained from HF radars, and now is being extended to use remote sensing images. In this case, the surface currents are determined together with subsurface currents from the dynamic and conservation equations, as opposed to tracking or correlating image patterns in time. Alternatively, the surface data can be assimilated into a numerical coastal ocean model that solves for depth-dependent currents. But, presently, efficient assimilative computation appears to be feasible only with depth-integrated ocean models. In this case, a method can be developed to obtain current structure from the depth-integrated solution via the use of surface and bottom boundary stresses and associated shear equations. This method of determination can be practical as it requires only the depth-integrated solution and surface and bottom boundary conditions at the location of interest as input, in contrast to conventional modeling approach of determining currents over the whole model domain. Demonstration of the use of the various methods noted here will be given by means of numerical examples and comparisons with some field experimental data