Acoustic Doppler current profiler
An acoustic Doppler current profiler (ADCP or ADP) is a hydroacoustic current meter similar to a sonar, attempting to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column. The term ADCP is used synonymously for all kind of acoustic current meters although the abbreviation originates from the name of an instrument series by Teledyne. ADCPs have been commercially available since the late 1980s. The working frequencies range from 38 kHz to several megahertz.
Working principle
ADCPs contain piezoelectric oscillators to transmit and receive sound signals. The traveling time of sound waves gives an estimate of the distance, the red or blue shift can be converted to a velocity. To measure 3D velocities, at least three vector components have to be estimated, this is why the instrument typically has four of them.
Further components of an ADCP are an electronic amplifier, a receiver, a mixer, a clock to measure the traveling time, a temperature sensor, a compass to know the relative rotation, and a pitch/roll sensor to know the horizontal. An analog-to-digital converter and a digital signal processor are required to sample the returning signal in order to determine the Doppler shift. A micro processor evaluates the sound velocity at the instrument position using the seawater equation of state, and uses this to estimate the velocities. This procedure assumes that the same density in the water column nearby is mainly determined by temperature, i.e. that the salinity has a preconfigured constant value. Finally, the results are saved on a memory card.
