The IEEE Seventh Working Conference on Current Measurement Technology

Current and Wave Monitoring and Emerging Technologies

March 13-15 | Bahia Hotel | San Diego, CA, USA

  
     

Design considerations of an acoustic-travel-time current sensor on a profiling free vehicle

Fred Thwaites

Status: Accepted

Woods Hole Oceanographic Institution
MS 18, 101 Smith Bldh.
Woods Hole, , MA USA
02543

Phone: (508) 289-3351
Email: fthwaites@whoi.edu

Co-Authors:
Kurt Polzin
MS 21, 344A Clark Bldh.
Woods Hole, MA USA
02543

We are building a second-generation High-Resolution Profiler to make vertical profiles of water velocity over scales from microstructure to full-ocean depth, to measure internal waves and turbulence. The profiler will measure microstructure with shear probes, fine structure with an acoustic-travel-time current sensor, large-scale water velocity with an electromagnetic field sensor, and profiler motion with accurate
accelerometers, compass, and GPS to get positions at the start and end of a profile. This paper discusses some of the design considerations of the acoustic current sensor and it's interaction with the vehicle. We are using modified MAVS electronics to make the measurement with a sensor head that is customized for this application. The acoustic path-length has been increased to 25 cm to improve accuracy. Estimates are made of the flow distortion in the measurement volume due to the profiler bow and flow disturbance from the sensor itself. Structural flow-induced vibration of the sensor and profiler result in noise in current measurement and can reduce the profiler sensitivity to low levels of turbulence. The sensor, its mounting to the profiler, and the profiler structure itself were made stiff, and the profiler shortened to raise the lowest structural vibration mode to nearly 30 Hz., above the frequency range most sensitive for measuring turbulent dissipation.

Submitted on November 19, 2002