A Microstructure Instrument for Profiling Oceanic Turbulence in Coastal Bottom Boundary Layers

Abstract

A free-falling instrument has been built to measure temperature, salinity and turbulent shear from near surface to within 15 cm of the ocean bottom. A probe guard mounted at the lower end of the instrument protects sensitive shear and temperature sensors from bottom sediments. The noise level in the shear signal corresponds to a dissipation rate of 3.0 × 10⁻⁷ W m⁻³, with vibrations of the probe guard providing the largest component of the noise. The signals are transmitted through a neutrally buoyant line to the ship where they are displayed in real time and recorded for later analysis. The profiling technique is capable of 20 profiles per hour through 50 m of water. Simultaneous profiles of turbulent microstructure and density can now be consistently obtained through the entire water column.