The Doppler method of measuring local velocities using lasers

The article reviews research on a new optical method, based on the Doppler effect, of investigating flows of liquid and gases. The connection between the statistical characteristics of the photocurrent and the statistical characteristics of a stream contain light-scattering particles is discussed. Methods are considered for the separation of the Doppler frequency shift, which contains information on the local flow velocity, viz., photomixing, direct photodetection, and optical spectral analysis. The most frequently employed systems of Doppler optical velocity meters are described for laminary and turbulent flows of liquid and gases, at both subsonic and supersonic velocities.