DARTS (Digital Automated Radar Tracking System): Application to Tidal Inlet Hydrodynamic Studies

Abstract

The mapping of strong tidally driven currents and waves through navigable inlets and restricted channels has proven to be both difficult and costly. The placement of semipermanent moored current meters and directional wave gauges is often logistically difficult, and, if measurement of surface currents is desired, poses an additional hazard to navigation. In addition, analysis of post-experimental current and wave records often requires substantial time and effort. Recent advances in digital radar technology have made possible the development of a remote ocean probe specifically designed to acquire high quality wave and current data in realtime: the Digital Automated Radar Tracking System (DARTS). DARTS was developed to provide coverage of relatively large ocean and inlet regions from a single shore monitoring station. In the wave measuring mode, DARTS acquires a spatial mapping of radar return intensities from the steep faces of approaching ocean surface waves. From this matrix of sea surface return intensities, a spatial Fast Fourier Transform (FFT) is applied to obtain an estimate of the directional wavenumber spectrum for the incident sea surface. In the current measuring mode, passive drogue floats equipped with radar reflectors are used to produce automatically Lagrangian trajectories and velocities. Remote current mapping of inlet regions up to 30 km has been completed successfully with the DARTS system. DARTS has been deployed successfully in the wave measuring mode as part of the SUPERDUCK 86 Field Experiment at the Coastal Engineering Research Center’s Field Research Facility at Duck, NC, and in the current monitoring mode in Upper Cook Inlet, AK, to map the strong tidally driven circulation in that region.