An acoustic Doppler current profiler sends sound pulses along three or four slanted beams and measures the Doppler shift of echoes from particles drifting with the water. Sorting the returns by travel time gives velocities in a stack of depth cells, so one instrument profiles the whole water column. ADCPs are bottom-mounted looking up, mounted on vessels looking down, or fixed sideways on piers to watch a channel.
ADCP on the channel floor shows the ebb running 2.8 knots near the surface and half that near the bottom.
Bottom-mounted ADCPs cannot see the top few percent of the water column because of sidelobe interference, so surface current is extrapolated, not measured.
Also heard as
- acoustic Doppler current profiler
- ADP
- current profiler
- H-ADCP
Related terms
Bin
One depth cell of an ADCP profile, the slice of water over which a single velocity is averaged.
Current ellipse
The ellipse traced by the tip of a tidal current vector over one cycle, showing direction and speed at each stage.
Tidal current
The horizontal flow of water that accompanies the rise and fall of the tide.
Harmonic analysis
Breaking an observed water level or current record into its tidal constituents to find each one's amplitude and phase.