ADS Environmental Services Model 4000 530017 A0 - Manual (Page 23)

System Overview 2-11
upward into the flow. The sound wave bounces off particles in the
flow and returns to the sensor. The velocity sensor measures the
change in the sound wave's frequency from transmission to
reception. This change is used to determine the velocity of the flow
based on the Doppler effect.
The Doppler effect describes the shift in frequency of a sound wave
emitted by a moving object in relation to a stationary point. In this
case, the moving objects are particles in the flow, the stationary
point is the velocity sensor, and the received signal is the reflection
of the sound wave (emitted by the velocity sensor) off the particles.
Doppler velocity sensor sending signals reflecting off particles in the flow