A three dimensional coherent Doppler velocity profiler: Bistatic beam geometry and calibration results

The authors report on a 1.7 MHz coherent Doppler sonar system designed for nearshore environments that provides three dimensional velocity profiles over a ≃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/second in 0.7 cm depth bins, vertical velocity accuracies of order 1 cm/s are achieved. For the horizontal components (based on bistatic measurements) standard deviation in velocity estimates of about 5% are realized with absolute accuracies of a similar magnitude. Accurate velocities from the bistatic configuration are critically dependent on transducer beam geometries. The authors outline their approach for determining the exact sample volume for the acoustic system