How ADCPs Work
ADCPs measure water motion by transmitting sound at fixed frequency. The
instrument measures the Doppler-shifted echoes backscattered from scatterers
(plankton and sediment) in the water and converts the echoes to along (acoustic) beam
velocity components. The ADCP then converts the along beam velocities to
north/south, east/west, and vertical velocity components. Velocity profiles
are determined by range gating echoes so that velocities are determined at
preset intervals along the acoustic path (called bins). Velocity
measurements with as little as 5 cm bin size are possible with the Broad Band
version of the ADCP operating in certain high resolution modes.
For more details about recent U.S. Geological Survey field work, please see: