Accession Number : ADA307806

Title :   Development of an Acoustic Vorticity Meter to Measure Shear in Ocean-Boundary Layers.

Descriptive Note : Doctoral thesis,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE

Personal Author(s) : Thwaites, Fredrik T.

PDF Url : ADA307806

Report Date : SEP 1995

Pagination or Media Count : 191

Abstract : This thesis describes the analysis and development of an acoustic vorticity meter to measure shear in ocean boundary layers over smaller measurement volumes than previously possible. A nonintrusive measurement of vorticity would filter out irrotational motion such as surface waves and currents that can swamp small scale measurements of shear. The instrument measures three axis vorticity at 0.83 and 2.45 meters below the ocean surface with measurement volumes of 0.45 meters on a side. The instrument forms a buoy that is inertially instrumented to calculate and remove buoy motion from the measurements. The instrument uses a complementary filter algorithm to estimate attitude and motion from low power, inexpensive, strapdown rate gyros, accelerometers, and fluxgate magnetometers. The instrument performance has been measured to have a vorticity bias of not more than 1 x 10(exp -2) per second in the down wave and vertical directions in typical ocean waves, and a 30 decibel spectral rejection of surface wave velocity. Two instrument deployments are described to show the potential of the system, one in the upper ocean boundary layer to measure shear and infer vertical diffusivity, and one on the thermocline to measure the Gradient Richardson number.

Descriptors :   *VORTICES, *MEASURING INSTRUMENTS, *FLOWMETERS, *BOUNDARY LAYER FLOW, VELOCITY, ALGORITHMS, DEPLOYMENT, ACCELEROMETERS, THESES, STRAPPED DOWN SYSTEMS, THERMOCLINES, SHEAR FLOW, BUOYS, MAGNETOMETERS, RICHARDSON NUMBER.

Subject Categories : Physical and Dynamic Oceanography

Distribution Statement : APPROVED FOR PUBLIC RELEASE