Ultrasonic Doppler Method

The ultrasonic velocity profiler (UVP) mainly employs the ultrasonic Doppler method to obtain a one-dimensional velocity profile. The measurement position is a function of time-of-flight of the ultrasonic pulses, and the velocity is obtained from the Doppler shift frequency. The principle and the method to detect the Doppler shift frequency are described in Sect. 3.1. When we use UVP for measuring velocity profiles in real situation, selections of the ultrasonic basic frequency, transducer setting, and ultrasonic reflectors are important, as shown in Sect. 3.2. Attention to be paid for measuring velocity is described in Sect. 3.3. Velocity aliasing appears if the velocity is over the maximum velocity defined by the Nyquist sampling theorem. We have to set a transducer carefully to avoid multiple reflections from surroundings. Temperature directly affects the measurement accuracy because measurement positions and velocities are functions of sound speed, and we also have to pay attention to the effects of solid boundary and measurement volume.