Remotely sensed surface currents in Monterey Bay from shore‐based HF radar (Coastal Ocean Dynamics Application Radar)

Abstract

Near‐surface currents in Monterey Bay derived from a network of shore‐based HF radars are presented for August–December 1994 and compared with those from April to September 1992. Focus is placed on the low‐frequency (2‐ to 30‐day period) motions in the remotely sensed data and on comparison of radar‐derived currents with moored current and wind observations, ship‐based acoustic Doppler current profiler observations, satellite‐based surface temperature imagery, and surface drifter velocities. The radar‐derived picture of the late summer mean flow is very similar in the two realizations and is consistent with historical data. Flow is equatorward in the outer part of the bay, poleward in a narrow band nearshore, and very sluggish in the middle of the bay. Low‐pass‐filtered time series of radar‐derived currents are highly correlated with moored current observations and with winds in the outer part of the bay. The vector time series are also coherent across a broad frequency band with currents typically in phase between 1‐ and 9‐m depths and with 1‐m currents typically 40°–60° to the right of the wind. Overall, these results confirm the utility of Coastal Ocean Dynamics Applications Radar (CODAR)‐type HF radars for the study of coastal surface currents out to ranges ∼50 km from shore, particularly for highly averaged fields. Data variability and comparison with in situ observations for high‐frequency (1‐ to 48‐hour period) motions point to the need to better characterize and minimize sources of error in the radar observations.

Blending HF radar and model velocities in Monterey Bay through normal mode analysis

“…Spatial coverage variability is typical of HRD observations. CEDAR measurements of surface velocity vary in their spatial coverage over time for a variety of reasons discussed by Paduan and Rosenfeld [1996]. Although both the size of the radar footprint and the uniformity of data coverage within the footprint show time variations, variations in footprint size are most troublesome.…”

“…The processed CEDAR data we use come from a uniform grid with a horizontal resolution of 2 km. A detailed description of the CO-DAR observations and an analysis of the low-frequency motions they describe are given by Paduan and Rosenfeld [1996]. Although their data could not be used to report an expected accuracy of CEDAR measurements, they did make quantitative comparisons between filtered CEDAR observations and ADCP current measurements, reporting rms speed differences Figure 1) were moved inward by four grid points from the true model boundary to ensure that nowcast boundary velocities will be determined by the model's dynamics and will not be strongly influenced by the model's radiation boundary condition.…”

Ocean forecasting for the German Bight: from regional to coastal scales

“…With their large area coverage, high resolution in time and space, and long-term operational capabilities, the radar systems have enhanced the coastal ocean monitoring capabilities for surface currents (Paduan and Rosenfeld, 1996) and have enabled the development of new data products. The value of HF radar data for the investigation of circulation in the German Bight was demonstrated by Carbajal and Pohlmann (2004) and Port et al (2011).…”

HF Radar Activity in European Coastal Seas: Next Steps toward a Pan-European HF Radar Network

“…In general an HFR sends out modulated radio waves and listens to the returned signal, which is mainly affected by the surface waves propagating along radar look direction that are of the order of the transmitted wave length (Bragg scattering). From the measured backscatter several oceanic parameters can be obtained, such as: ocean surface currents (e.g., Paduan and Rosenfeld, 1996;Gurgel et al, 1999;Shrira et al, 2001), waves (e.g., Wyatt et al, 2006), winds (e.g., Shen et al, 2012), tsunami (e.g., Lipa et al, 2006) and discrete targets (ships) (e.g., Maresca et al, 2014).…”