Optical and Acoustical Measuring Techniques

  • William C. Cliff


In recent years considerable emphasis has been placed on developing techniques to remotely measure the velocity of confined and free fluid flows (such as atmospheric, oceanic, wind tunnel, blood, pipe, and channel flows, etc.). The laser Doppler and acoustic Doppler are two techniques that will be examined in this chapter. Both techniques are based on the Doppler effect. The Doppler effect is the fact that there is a change in frequency with which energy reaches a receiver when the receiver and the energy source are in motion relative to one another. In the cases of the laser and acoustic Doppler system, energy is transmitted to a moving scatterer (tracer), which then becomes a source, and the energy is transmitted to a receiver. The Doppler systems measure the velocity of these scattering sources and, therefore, the accuracy with which the Doppler systems measure fluid velocity is dependent upon the accuracy with which the imbedded scattering source follows the true velocity of the medium. Major efforts in the development of the laser and acoustic Doppler systems have been underway since the 1960’s.(1–3) It is the intent of this chapter to skip the developmental years of these systems and present the techniques that are presently employed and the results that they are obtaining.


Doppler Frequency Scattered Radiation Fringe Pattern Local Oscillator Dust Devil 
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Copyright information

© Plenum Press, New York 1977

Authors and Affiliations

  • William C. Cliff
    • 1
  1. 1.George C. Marshall Space Flight CenterNational Aeronautics and Space AdministrationHuntsvilleUSA

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