Microstructure profiler to study mixing and turbulent transport processes

The MST (Microstructure-Turbulence) Profiler is a newly developed operational microstructure measuring system for marine turbulence measurements. The profiler can be used for sinking and uprising measurements and is equipped with a new type of current shear sensor. The authors have tested the MST Profiler in several field measuring campaigns. The investigations were focused on the internal vibration level of the profiler and its lower detection limit for dissipation rate estimates (pseudo dissipation). The test measurements gave no indication of pronounced internal profiler vibrations interfering with dissipation measurements. The pseudo dissipation level (noise) of the profiler was found to be as low as 5.10^-12 W/kg under quiet conditions at sinking velocities below 0.4 m/s. At 0.8 m/s sinking velocity, a pseudo dissipation of 4.10^-11 W/kg was obtained. At rising measurements with additional sources of profiler vibrations the pseudo dissipation is about twice that for sinking measurements. The upper detection limit was estimated based on the geometry of the shear sensor. Dissipation rates up to 10^-4 W/kg can be measured without correction for unresolved variance of the shear spectrum