A three-dimensional coherent Doppler profiler

Abstract

A 1.7-MHz coherent Doppler sonar system has been designed for near-shore environments that provides three-dimensional velocity profiles over an O (0.5-m) depth range. The use of a bistatic geometry allows three independent components of velocity to be measured simultaneously in time and coincident in space. The system was calibrated in a tow-tank facility for velocities up to 2 m/s. For multiple pulse-pair ensemble-averaged velocity estimates generated at a rate of 30 profiles/s in 0.7-cm-depth bins, vertical velocity accuracies of the order 1 cm/s are achieved. For the horizontal components (based on bistatic measurements), standard deviation in velocity estimates of about 5% is realized with absolute accuracies of about 2%. In the configuration as tested, flow disturbance around the instrument introduces a bias of about 5%: this disturbance is modeled using potential flow past a cylinder. The disturbance errors could be corrected to the free-stream velocities using the present data set. Such a correction would not, however, reflect the actual water speed at the point of measurement. [This research was funded by the Office of Naval Research Coastal Sciences Program, and the Natural Sciences and Engineering Research Council of Canada.]