A family of acoustic vorticity meters to measure ocean boundary layer shear

The authors have developed several three axis acoustic vorticity meters at the Woods Hole Oceanographic Institution for measuring shear and turbulence in ocean boundary layers. Such a measurement, in principle, filters out irrotational motion such as linear surface gravity waves which can swamp measurements of a flow´s rotational motion. The authors have constructed one 15 cm acoustic path instrument, four 45 cm path instruments, and one 1.5 m path instrument and established their accuracy in a series of laboratory and ocean experiments. The 15 cm acoustic path instrument has a mean flow induced vorticity error of 0.034/s in a flow of 0.369 m/s and 20 dB rejection of waves. The 45 cm path instruments have an uncalibratable 10^-2/s mean flow induced vorticity error in a constant flow of 0.7 m/s consistent with the theoretical prediction that accuracy improves with increased path length. The 45 cm path instruments have been deployed in the ocean upper boundary layer to measure shear, in the thermocline to measure internal waves, and in the bottom boundary layer to measure turbulence