A three-component bistatic coherent Doppler velocity profiler: error sensitivity and system accuracy

We report on a 1.7-MHz coherent Doppler sonar system designed for near-shore environments that provides three-component velocity profiles over an O(1-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 horizontal 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, the standard deviation in measured vertical velocity is about 1% of the total flow speed. For the horizontal components (based on bistatic measurements), the standard deviation of velocity estimates is about 5%. Absolute accuracies are also about 5% of the speed but a portion of this bias is caused by flow disturbance around the instrument package: this disturbance is modeled using potential flow past a cylinder