Development of a modular acoustic velocity sensor

The authors are developing a Modular Acoustic Velocity Sensor (MAVS), a three-axis current meter that measures the differential acoustic-travel time in a small measurement volume. The requirements of this sensor are: low cost, small size, high accuracy, good cosine response to current direction, lack of bias in a wave environment, ability to measure turbulence and the Reynolds stress, resistance to fouling, ability to measure near a boundary, and accuracy at low current speeds. The sensor is a derivative of the Benthic Acoustic Stress Sensor (BASS) which has been very successful at measuring currents, shear, and Reynolds stress. A first MAVS sensor prototype has been built and tested. The sensor was designed to reduce flow disturbance error when flows are steeper than thirty degrees from the horizontal. This paper describes performance measurements of the first prototype sensor. The sensor was towed in a tow tank to measure its accuracy and to characterize the vortex shedding noise inherent in any flow measurement made local to an ocean sensor. The first prototype was found to have better cosine response but more flow noise than BASS. A second prototype is now being built to have better cosine response than BASS and lower noise than the first prototype