TEST MEASUREMENTS WITH AN OPERATIONAL MICROSTRUCTURE-TURBULENCE PROFILER - DETECTION LIMIT OF DISSIPATION RATES

The MST (Microstructure-Turbulence) Profiler is a newly developed oper ational microstructure measuring system, specially designed for marine and limnic turbulence measurements. The profiler can be used for sink ing and uprising measurements and is equipped with a new type of curre nt shear sensor. We have tested the MST Profiler in several field meas uring campaigns in deep Alpine lakes. The investigations were focused on the internal vibration level of the profiler and its lower detectio n limit for dissipation rate estimates (pseudo dissipation). The upper detection limit was estimated based on the geometry of the shear sens or. The test measurements gave no indication of pronounced internal pr ofiler vibrations interfering with dissipation measurements. The pseud o 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 mis. At 0.8 mis sinking velocity, a pseudo dissipation of 4.10(-11) W/ kg was obtained. At rising measurements with additional sources of pro filer 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.