Surface-to-subsurface velocity projection for shallow water currents

Sea surface currents in coastal oceans are accessible to continuous direct observations by shore-based high-frequency Doppler radar systems. Inferring current structure in shallow water from such surface current observations is attempted. The approach assumes frictionally dominated Row and verticall y varying current velocity on the scale of the Ekman boundary layer. The ap proximation of the velocity variation with depth is consequently derivable in terms of orthogonal basis functions from the sea surface kinematic and d ynamic boundary conditions; specifically, the viscous momentum and shear eq uations evaluated at the sea surface. The inference procedure developed is demonstrated with sea surface data obtained in the coastal High-Resolution Remote Sensing Experiment on the continental shelf off Cape Hatteras. Despi te uncertainties in the surface measurements, qualitative agreement is obta ined between the inferred subsurface current and the current measured in si tu. The sensitivity of the inference to the measurement uncertainties as we ll as to the model assumptions is investigated, and the inferred result is found to be generally robust.