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San Francisco Bay (Region 1) Surface Currents
Program: Coastal Ocean Currents Monitoring Program
Sensor: CODAR HF Radar
Primary Geophysical Parameter: Surface Current velocity
Nominal Accuracy: unknown
Spatial grid: 0.025 degrees longitude by 0.025 degrees latitude, geographic
Spatial coverage: Coastal waters off San Francisco Bay
Temporal Coverage: Aug, 2006 - ongoing
CoastWatch distributes surface current velocity data for the San Francisco Bay region generated by a network of CODAR High Frequency (HF) radar stations. These currents are generated as part of the Coastal Ocean Currents Monitoring Program. More specifically, these currents are generated by the Naval Postgraduate School (Professor Jeffrey Paduan, Principal Investigator) and San Francisco State University's Romberg Center for Environmental Studies (Professor Newell T. Garfield, Principal Investigator) as part of the Central California region of the Coastal Ocean Currents Monitoring Program. Current data are valuable in addressing environmental emergencies such as oil spills or pollution releases and other ocean-related issues such as search and rescue operations. This is an EXPERIMENTAL dataset, distributed for scientific evaluation.
The source data are processed to surface current as in Paduan and Rosenfeld, 1996. The HF radar transmits a pulse and measures the resulting Bragg scattering. A Bragg backscatter results only from waves of specific wavelength that are traveling along the direction of travel of the radar pulse. The theoretical wave speed is calculated from this backscattered wavelength and the deep water dispersion relation. The HF radar station also measures the Doppler shift of the backscatter signal and calculates wave speed from the Doppler shift. Surface current is the difference between theoretical wave speed calculated from wavelength and the deep water dispersion relation and wave speed calculated from the Doppler shift of the backscatter radar signal.
An important limitation of this measurement technique is that it only measures the radial current velocity, the component of surface current towards or away from the HF station. Measurements from more than one HF station are needed to generate the absolute current velocity at any one point within the bay. By combining measurements from multiple stations, the total velocity grid is generated.
To fill in gaps in current velocity measurements in the total velocity grid, a normal mode analysis technique is used (Lipphardt et al., 2000, see http://newark.cms.udel.edu/~brucel/nma/index.html), resulting in a complete objective mapping grid with fewer data gaps.
Despite our best efforts, incorrect data may often appear within near real time data sets. NOAA CoastWatch accepts no liability for use of these data products. It is recommended that these products NOT be used for navigation.
If this data is used for presentation or publication, please acknowledge the University of Delaware and the Naval Postgraduate School.
References and suggested citations:
Lipphardt, B. L. Jr., A. D. Kirwan, Jr., C. E. Grosch, J. K. Lewis, J. D. Paduan. 2000. Blending HF radar and model velocities in Monterey Bay through normal mode analysis. J. Geophys. Res, vol. 105, pp. 3425-3450.
Paduan, J.D. and L.K. Rosenfeld. 1996. Remotely sensed surface currents in Monterey Bay from shore-based HF radar (CODAR), J. Geophys. Res., vol. 101, no. C9, pp. 20,669-20,686.