HF Radar

HF radar maps ocean surface currents from shore by reading the Bragg backscatter of high-frequency radio waves off surface gravity waves half the radar wavelength. Operating between roughly 3 and 50 MHz, a coastal site senses the radial current component, the speed toward or away from the antenna, out to 30 to 200 km depending on frequency, with finer range and shorter reach at higher frequency. Two or more sites combine their radials into a two-dimensional surface-current vector field. Systems such as CODAR SeaSonde feed real-time current maps for search and rescue, oil-spill drift, and harbor safety, the only routine source of synoptic nearshore surface currents.