Mapping coastal winds with HF radar

Over-water wind speeds and directions derived from a ground-wave high frequency radar-the Multi-frequency Coastal Radar (MCR)-are compared to in-situ observations to examine the skill of the radar measurements. Conventional beam formation processing of radar data collected from two sites around Monterey Bay during summer 1997 is used to produce wind directions based on the relative strength of the positive and negative Bragg-resonant peaks, which correspond to wind-driven waves approaching and receding from the radar, respectively. The functional relationship that converts these signal levels, which primarily reflect surface wave conditions, to a wind direction are a central research issue. To address this issue, the remotely sensed estimates are compared against moored observations under variable wind conditions. Wind direction algorithms based on Bragg ratios applied to this or any HF radar cannot detect wind speed. However, the unique capability of the MCR to, simultaneously, measure at four Bragg-resonant frequencies is used to assess the sensitivity of near-surface current shear to the measured wind speed.