The steps in the development of an atmospheric vorticity meter

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Singleton, Thomas W.
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This thesis describes the steps necessary to develop an acoustic vorticity meter for the atmosphere. The analysis is based on Benthic Acoustic Stress Sensor (BASS) technology that is currently used for similar acoustic measurements in the ocean. Compared to sonic anemometer measurements, the BASS measurements of velocity are not only made in a different fluid but in a different way. Due to these differences, the physical make up of BASS needed to be altered, and the validity of the measurement technique had to be explored. The alterations to the BASS hardware occurred for several reasons. Because attenuation of sound is much higher in air than in water for the same frequencies, it was necessary to change the transducers. The generally faster and unidirectional mean flows that are present in the air encourage open measurement volumes which the BASS vorticity meters do not have. The difference in group speed of sound is different for water and air, and this forced a change to the timing and burst generation board of the BASS vorticity meter. The measurement technique used by the BASS instrumentation is validated by the error analysis in the text. Because the BASS instrumentation actually provides a time difference, the equation used by the BASS instrumentation to compute velocity was assumed throughout the error analysis. The error analysis shows that the combination of BASS measurement techniques with a temperature sensor will provide errors that are less than 2% of the velocity. The types of measurements that an atmospheric vorticity meter would provide to a researcher are described in the text to show the meter's potential. If deployed on a buoy, a vorticity meter could measure shearing of the wind close to the surface of the waves. If deployed at heights much greater than its path lengths, an atmospheric vorticity meter could provide three-dimensional vorticity measurements which would provide a unique measurement of a fundamental characteristic of turbulent flows.
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1995
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