How it works
We measure ocean currents by emitting radio waves from shore-based transmitting antennas that travel along the ocean's surface. The radio waves are scattered by the rough surface of the ocean (ocean waves) and part of the scattered energy returns like an echo to a receiving antenna.
The received echoes contain information about the range, direction, and speed of the current in relation to the antenna location. Combining this information from two or more antennas allows us to construct surface maps of current speed and direction.
Although the technology we use to measure ocean currents is typically called "High Frequency Radar" of "HF Radar", a more accurate name is "HF Radio". Ocean current transmitting antennas operate at similar frequencies to broadcast radio and TV, but at much lower power levels (0.1% or less). The transmitted energy, comparable to the power of a household light bulb, is harmless to humans and animals.