ADCPs

An acoustic Doppler current profiler (ADCP) is an oceanographic instrument that measures velocity throughout the water column by emitting acoustic pulses and analyzing the Doppler shift of backscattered sound from moving particles in the water. The instrument uses multiple acoustic beams, typically four, oriented at fixed angles to the vertical. By comparing the Doppler shifts along each beam, the device resolves velocities into earth-referenced components, usually horizontal (u, v) and vertical (w), after applying tilt and heading information.

ADCPs are deployed in several configurations. Moorings hold the instrument in a fixed position to monitor time series of current profiles. Lowered from a ship or buoy, it can acquire profiles as it moves through a depth range. Hull-mounted and towed ADCPs collect data while the host vessel or vehicle is in motion, enabling broader spatial surveys. Frequencies commonly range from about 75 to 300 kHz for high-resolution, near-surface measurements, with lower frequencies used for deeper water. Some systems offer multiple frequency channels or adjustable settings to balance range and resolution.

Data products include velocity profiles as a function of depth, produced at chosen bin sizes, along with backscatter intensity that can indicate turbidity or particulate content. Processing involves ensemble averaging, quality control, and corrections for instrument tilt, compass heading, and sound speed. Data quality can be affected by attenuation, bottom reflections, and insufficient scattering particles, which can create blind zones near the surface or bottom.

Applications span oceanic, estuarine, and riverine studies, including coastal circulation, boundary layer dynamics, and discharge estimation. The main advantages of ADCPs are non-intrusive, continuous, high-resolution measurements over extended periods and depths, while limitations include reliance on adequate scattering particles and sensitivity to environmental conditions and instrument installation.