Summary of Findings for using High Frequency Radar in Physical Oceanographic and Ecological Studies

The performance of a network of five CODAR (Coastal Ocean Dynamics Application Radar) high frequency (HF) radars is described based on comparisons with an array of nine moorings in the Santa Barbara Channel and Santa Maria Basin deployed between June 1997 and November 1999. Eight of the moorings carried vector measuring current meters (VMCM’s), the ninth an upward-looking acoustic Doppler current profiler (ADCP). Coverage areas of the HF radars and moorings included diverse flow and sea state regimes. Measurement depths were ~1 m for the HF radars, 5 m for the VMCM’s, and 3.2 m for the nearest ADCP bin to the surface. Comparison of radial components of near-surface currents from 18 HF radar-mooring pairs yielded root mean square (rms) speed differences of 7-19 cm s. The radial components were significantly correlated with r in the range 0.39-0.77. Other studies based on radar-mooring comparisons have found similar rms speed differences and r based on total velocity vectors. Spectral analysis showed significant coherence for frequencies below 2.3 cycles day (periods longer than 11 hr). At higher frequencies no significant coherence was found. Comparisons revealed bearing errors in locating radial currents on the sea surface by some of the HF radars. These were typically 510° with a maximum error of 19o. The effects of bearing errors on total velocity vector estimates were evaluated using a simple flow field and measured bearing errors, showing up to 15% differences in computed flow speeds, and up to ~9o differences in flow directions.