| Summary: | The archival package contains ocean surface radial velocities collected from High frequency (HF) radar stations. NDBC, which with SIO assembles data from the IOOS HF Radar Network, submits these data monthly to NCEI as part of NCEI's Integrated Ocean Observing System Data Assembly Centers (IOOS DACs) Data Stewardship Program. Radial velocity files contain metadata in a key-value format while the measured velocities and associated ancillary data are reported in a tab-delimited format. Remote sensing of ocean surface velocity from shore-based HF radar sites bridges an operational observational gap between point samples obtained from in-situ sampling and synoptic scale relatively low resolution data obtained from satellites by providing continuous mesoscale coverage at relatively high resolution near the coast. HF radar systems measure the speed of ocean surface currents in directions radial to the antenna in near real time. Radial measurements of ocean velocity may be used directly in some applications such as model assimilation but are commonly used in combination with overlapping sites to estimate the total vector ocean velocity. Radial velocities alone are a measurement of surface ocean velocity projected along the direction radial to the antenna. Systems operate continuously in all weather conditions and are installed near the coastline. Range resolution of measured currents is determined by the radar transmit bandwidth used. Bandwidth is controlled by radio frequency licenses and translates to range resolutions of 0.5 to 6 kilometers. Maximum ranges of current measurements also depend on radar transmit frequency and vary from about 40 km offshore to about 200 km offshore. Velocities are measured in the upper 0.3 - 2.5 meters of the ocean depending on the operating frequency and vertical velocity shear profile.
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