MICROSTRUCTURE PROFILER TO STUDY MIXING AND TURBULENT TRANSPORT PROCESSES zyx Hartmut Prandke ISW In Situ Wassermesstechnik,Petersdorf, Germany Adolf Stips Space Applications Institute, zyxwvut JRC, Ispra, Italy Abstract zyxwvutsrqpon - 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. We have tested the MST Profiler in several field measuring campaigns. The investigations were focused on the internal vi- bration 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''2 Wkg under quiet conditions at sinking velocities below 0.4 zyxw ds. At 0.8 d s sinking ve- locity, a pseudo dissipation of 4.10-l' Wkg 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 W k g can be measured without correction for unresolved variance of the shear spectrum. I. INTRODUCTION In the framework of the zyxwvuts EUROhUR-MICSOS Project (EU 1246), a measuring system for microstructure and turbu- lence measurements has been developed. The MST Wcro- Structure-Turbulence) Profiler system is designed for op- erational measurements in marine and limnic environment and can be used by not specially trained personnel. The mi- crostructure measuring system is produced by the company ME Meerestechnik-Elektronik GmbH (Germany). The MST Profiler has been tested in several field measuring campaigns in the Baltic Sea, the North Sea and in deep Al- pine lakes. The investigations were focused on the internal vibration level of the profiler and its lower detection limit for dissipation rate estimates from turbulent current shear measurements. II. PROFILER CONSTRUCTION In Fig. 1 the basic system configuration is shown. The pro- filer is an instrument for simultaneous microstructure and precision measurements of physical parameters. It is de- signed for vertical profiling within the upper 100 m. The data are transmitted via electrical cable to an on board unit and further to a data acquisition PC. The profiler can be used for sinking operations, as well as for rising measure- ments. The main housing of the profiler consists of a cylindrical stainless steel tube with a length of 700 mm and a diameter of 155 mm. Both ends of the central part have caps with a reduced diameter of 108 mm. This gives a total length of the housing of about 1000 mm. The housing is pressure tight to 1 Mpa (- 100 m). A ring of brushes is placed at the upper end of the probe (cable end) to give it drag and righting-torque. Adjusting weights can be fixed at both ends of the housing. This allows to give the profiler differ- ent buoyancy. For vertical sinking measurements, the profiler is balanced with a slightly negative buoyancy which gives it a sinking velocity between about 0.4 and 0.75 m/s (recommended by the manufacturer of the profiler). The profiler is manually handled and recovered. Effects caused by cable tension (vibrations) and the ship's movement are excluded by a ca- ble slack. For rising measurements, the MST Profiler is given a posi- tive buoyancy. It is operated via a remote controlled under- water winch. To guaranty free movement of the profiler, an additional buoyancy body near to the profiler carries the weight of the cable and produces a cable slack just below the rising instrument. Uprising measurements near the shore line or in narrow limnic waters have been carried out having the winch on land. In this case, a guide pulley was placed on the bottom at the investigation site. The MST Profiler is equipped with microstructure sensors, standard CTD sensors for precision measurements, and a vibration control sensor (see table 1). The sampling rate for all sensors is 1000 samples per second, the resolution 16 bit. The sensors are mounted at the lower end of the probe (sensor end, Fig. 1). The microstructure sensors are placed at the tip of a slim shaft, about 120 mm in front ofthe CTD sensors. 0-7803-5045-6/98/$10.00 0 1998 IEEE 179