Swell wave direction off Tweed Heads monitored by HF ocean surface radar

We present results of an analysis of data collected in coastal waters off Tweed Heads during an ocean surface monitoring survey using the HF Ocean Surface Radar (COSRAD). The radar was deployed for a 30-day period during February and March of 2001 to routinely measure surface currents and wind wave parameters. The deployment also offered an opportunity to develop techniques for measuring swell wave parameters. This paper presents theory and a case study showing how second order swell peaks are observed in the Doppler spectrum. COSRAD produces an entire sweep every 30 min with spatial resolution of the order of 3 km. We average 8 adjacent pixels over a 2 h period to produce swell parameters. Swell parameters are produced from second-order (sideband) energy near the strong first-order Bragg peaks in the spectrum. Space and time averaging is done to reduce spectral noise. Our analysis indicates that the COSRAD HF radar is suitable for monitoring swell in the near-shore zone