Water velocity and turbulence measurements by pulse coherent doppler sonar

A five-beam pulse-to-pulse coherent Doppler sonar capable of high space-velocity resolution measurements of water current mean velocity and turbulence has been developed and used extensively to monitor the characteristics of water flow. One beam is vertical thus providing direct measurements of the vertical component, w, of water velocity and turbulence. Horizontal velocity and turbulence measurements are made using two tilted beams contained in a vertical plane parallel to the longitudinal flow, and two other beams also tilted but contained in a plane perpendicular to that longitudinal flow. The paper presents the system and its performance including techniques to extend the maximum unambiguous range-velocity limits by use of dual-or tri-interleaved pulse repetition periods assisted by signal processing methods. Fast switching of the five beams, together with high elevation angle of the tilted beams (five degrees from vertical), reducing the horizontal separation distance between the five beams, allows individual estimates of the variance and covariance-Reynolds stress terms which both contribute to the measured Doppler spectrum variance.