Design considerations for a 3-d laser Doppler velocimeter for studying gravity waves in shallow water.

A laser velocimeter system using three frequency-modulated light beams and one detector for measurement of the instantaneous velocity vector in reversing flow is considered. An analysis of the scattering and detection processes by means of the Mie and optical mixing theories is outlined. A system proposed for gravity wave studies uses an argon-ion laser and three Bragg cells as a source and a photomultiplier detector of the light backscattered from 0.2-microm-diameter spheres, introduced into the flow in a low concentration, and can measure local velocity vectors.of magnitude between 0.1 m/sec and 3.0 m/sec, with turbulent fluctuations of 1% or greater intensity.