An Acoustic Doppler Current Profiler (ADCP) measures ocean currents using the principle of “Doppler shift.” If you have heard a train whistle in the distance, you are familiar with Doppler effect. As the train gets closer, the whistle pitch gets higher. As the train moves away, the whistle pitch gets lower. The change in pitch is proportional to the speed of the train.
An ADCP follows the premise of the Doppler effect. It emits a series of high-frequency pulses of sound that bounce off of moving particles in the water. If the particle is moving away from the instrument, the return signal is at a lower frequency. If the particle is moving toward the instrument, the return signal is at a higher frequency. Because the particles move at the same speed as the water that carries them, the speed of the water’s current can be determined.