Surface ocean velocities obtained by HF radar from stations located along coastal waters of Antarctica, Hawaii, North Slope Alaska, Puerto Rico/Virgin Islands, eastern US/Gulf of Mexico and western US during July 2015 (NCEI Accession 0138671)

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.

本档案数据包包含由高频（HF）雷达站采集的海洋表面径向流速数据。NDBC与SIO联合整合了IOOS HF雷达网络的观测数据，并每月将这些数据提交至NCEI，作为NCEI综合海洋观测系统数据汇编中心（IOOS DACs）数据管理计划的一部分。径向流速文件以键值对格式存储元数据，而实测流速及相关辅助数据则采用制表符分隔格式进行记录。

岸基HF雷达站开展的海洋表层流速遥感探测，通过在近岸区域提供连续的中尺度高分辨率观测覆盖，填补了原位采样获取的点样本与卫星获取的天气尺度相对低分辨率数据之间的业务化观测空白。HF雷达系统可近乎实时地测量沿天线径向方向的海洋表层流流速。海洋流速的径向测量结果可直接应用于诸如模式同化等部分场景，但通常会与重叠覆盖的雷达站数据结合，以估算完整的海洋矢量流速。仅依靠径向流速，仅能得到沿天线径向投影的海洋表层流速测量值。

该系统可在全天气条件下连续运行，并部署于近岸区域。实测海流的距离分辨率由雷达发射带宽决定，带宽受无线电频率许可管控，对应的距离分辨率范围为0.5至6千米。海流测量的最大探测距离同样取决于雷达发射频率，离岸探测范围约为40千米至200千米。依据工作频率与垂直流速切变剖面的不同，流速测量的海洋表层探测深度为0.3至2.5米。