Automatic calibrations for improved quality assurance of coastal HF radar currents

CODAR Ocean Sensors, Ltd. and the University of California, Santa Barbara are developing a method by which HF radar antenna response patterns can be calibrated automatically over time. Currently, over 130 HF radar units are providing coastal surface current maps to the public via the U.S. Integrated Ocean Observing System (USIOOS): http://www.ioos.gov/hfradar/. These real-time data are used for Coast Guard Search and Rescue, Hazardous Materials Spills Response, Water Quality Monitoring, Monitoring Harmful Algal Blooms, Fisheries Management, Modeling, Marine Navigation, Ocean Energy Production. Techniques for improved, automated quality assurance of the data provided by coastal radar stations, such as the one discussed here, will improve the efficacy of efforts in these areas. Passing vessels provide a steady supply of targets for which the echoes in the HF Doppler spectra can be used as source signals. The Automatic Identification System (AIS) transmissions from these vessels provide the position and, therefore, bearing to the vessel. By associating the known AIS positions with HF Doppler echoes, a low-cost calibration procedure can be implemented which can reduce or eliminate more labor-intensive alternatives. This method is demonstrated using data from mid-range systems in the Santa Barbara channel that are operating in the 13 MHz band. A prototype package has been deployed on a system monitoring the Gulf of Farallones and the shipping lanes approaching the San Francisco Bay. Performance and data quality metrics for this prototype will be discussed.