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 travelling 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.

Nortek Aquadopp Current Profilers uses 3 acoustic beams typically slanted at 25 degrees to measure the current profile. The internal tilt and compass sensors measure the direction of the current and the high resolution pressure sensor measures depth. If the system is fixed mounted, the pressure sensor can measure the tidal elevation. The HR Aquadopp Current Profiler measures the phase shift between two or more acoustic pulses. The instrument transmits a pulse and then records an echo to measure the velocity along each of the acoustic beams.