Acoustic Doppler Current Profilers (ADCP) are hydroacoustic instruments, similar to sonars. ADCPs use the Doppler effect of sound waves that are scattered by particles in seawater over a depth range. The traveling time of sound waves gives an estimate of distance, and the increase (blue shift) or decrease (red shift) in frequency is converted into water current velocities.

RDI Teledyne Acoustic Doppler current profilers are configured to monitor water currents at several frequencies. The instruments contain sensors for temperature, pressure, tilt and compass heading. RDI ADCPs use four beams to measure current velocity so that the fourth beam/transducer can substitute for a blocked or damaged beam or it can be used to increase data accuracy. The RDI Workhorse ADCP operating at 1200 kHz offer high vertical resolution with a typical range of 12 m.