Test measurements with an operational microstructure-turbulence profiler: Detection limit of dissipation rates

Abstract

The MST (Microstructure-Turbulence) Profiler is a newly developed operational microstructure measuring system, specially designed for marine and limnic turbulence measurements. The profiler can be used for sinking and uprising measurements and is equipped with a new type of current shear sensor. We have tested the MST Profiler in several field measuring campaigns in deep Alpine lakes. The investigations were focused on the internal vibration level of the profiler and its lower detection limit for dissipation rate estimates (pseudo dissipation). The upper detection limit was estimated based on the geometry of the shear sensor. 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 due to influence of the cable the pseudo dissipation is about twice that for sinking measurements. For the upper detection limit which can be measured without correction for unresolved variance of the shear spectrum, a value of 10-4 W/kg was estimated.