The RDI Acoustic Doppler Current Profiler (ADCP) employs the Doppler principle to measure speed and direction of currents in the water column below a moving vessel.

By transmitting a succession of acoustic pulses, and segmenting the resulting backscatter echoes into many depth cells (bins) over a depth range of 8 to 1000 meters, computer analysis of the bins provides a detailed profile of current speed and direction throughout the water column. In waters where the bottom depth is within range, the ADCP bottom track feature measures earth referenced vessel speed. Combination of these measurements yields absolute (earth referenced) vertical current profiles from a moving vessel without inputs from other navigation systems. The PC Windows  based VmData Acquisition System (VmDAS) processes the ADCP data in real time together with vessel attitude and heading data to produce vector averaged profiles in earth referenced coordinates. Data is displayed in real time on a monitor or can be played back at a later time.

The ADCP transmits acoustic pulses from a transducer assembly along four beams. The transducers receives backscattered echos from plankton and small particles riding the water currents. Using the Doppler effect and some basic trigonometry, the ADCP converts the backscattered sound into components of water current velocity. The ADCP measures the speed and direction of the current at multiple locations in the water column. The ADCP makes a profile of these measurements for up to 128 locations called depth cells or bins. Bins can be from 4 to 32 meters in length. For information on ADCP principles of operation and the Doppler effect, see RDI's Acoustic Doppler Current Profilers Principles of Operation: A Practical Primer. Appendix S has information on system specifications and dimensions. Appendix X has a functional description.