Acoustic Doppler velocimetry


Acoustic Doppler velocimetry is designed to record instantaneous velocity components at a single-point with a relatively high frequency. Measurements are performed by measuring the velocity of particles in a remote sampling volume based upon the Doppler shift effect.

Probe specs and features

The probe head includes one transmitter and between two and four receivers. The remote sampling volume is located typically 5 or 10 cm from the tip of the transmitter, but some studies showed that the distance might change slightly. The sampling volume size is determined by the sampling conditions and manual setup. In a standard configuration, the sampling volume is about a cylinder of water with a diameter of 6 mm and a height of 9 mm, although newer laboratory ADVs may have smaller sampling volume.
A typical ADV system equipped with N receivers records simultaneously 4.N values with each sample. That is, for each receiver, a velocity component, a signal strength value, a signal-to-noise and a correlation value. The signal strength, SNR and correlation values are used primarily to determine the quality and accuracy of the velocity data, although the signal strength may related to the instantaneous suspended sediment concentration with proper calibration. The velocity component is measured along the line connecting the sampling volume to the receiver. The velocity data must be transformed into a Cartesian system of coordinates and the trigonometric transformation may cause some velocity resolution errors.
Although acoustic Doppler velocimetry. Simply, "raw" ADV velocity data are not "true" turbulent velocities and they should never be used without adequate post-processing. Chanson presented a summary of experiences gained during laboratory and field investigations with both Sontek and Nortek ADV systems.