Acoustic Doppler current profiler-a sonar system to estimate currents and scattering

The acoustic doppler current profiler (ADCP) is standard equipment on many oceanographic research vessels. The sonar estimates the current using the Doppler shift of echoes from zooplankton present in the upper ocean. With the assumption that the targets are drifting with the current, and knowing the absolute velocity of the ship using the GPS satellite navigation system, profiles of the absolute current in the upper 300-500m of the ocean can be made routinely. A by-product of the current measurement is the strength of the backscattered signal, which forms the basis for the zooplankton abundance estimate. The data, which are digitally logged, are processed using shipboard computers to produce sections and maps of currents and scattering. Careful calibration is needed before scattering signal can be related to biomass. As examples of the use of shipboard ADCPs data are given for ocean current monitoring in the region of the Iceland Faeroes in July-August 1990 and for zooplankton abundance estimation in the region of the Indian Ocean atoll of Aldabra in 1987