Echoes of these pulses are backscattered from material suspended in the flow. As this material has motion relative to the transducer, the echoes are Doppler shifted in frequency. Measurement of this frequency enables the calculation of the flow speed. A fifth ceramic mounted in the center of the transducer assembly, and aimed vertically, is used to measure the depth. The ADFM divides the return signal into discrete regular intervals which correspond to different depths in the flow.
Velocity is calculated from the frequency shift measured in each interval.
The result is a profile, or linear distribution of velocities, along the direction of the beam. Each of the rectangular yellow segments in Figure 1 represent an individual velocity measurement in a small volume known as a depth cell. The directions of the velocity profiles in Figure 1 are based on the geometry of the ADFM s transducer assembly. Figure 2 shows a side view of the transducer assembly. The profiles shown in Figure 1 are generated from velocity data measured by an upstream and downstream beam pair.