Autonomous ocean turbulence measurements on a moored instrument in the South China Sea

A moored and autonomous test has been taken in the South China Sea(SCS) with a turbulence measurement instrument that measures small-scale shear velocity using shear probes designed by OUC(Ocean University of China). The MTMI (Moored Turbulence Measuring Instrument) is embedded in a raindrop shape floating body, which is made of buoyancy material of glass microsphere. A accelerate senor is used for vibration measurement and removing the vibration noise. The data which contain velocity signals, vibration noise and attitude signals are sampled for 110 days. The pitch angle varies between -10°and +10°and does not changes in response to variations of current speed, showing that the instrument is stable. The measured velocity spectra are severely contaminated by eddyshedding from the mooring cable. With the consideration that y axes might not be rigidly perpendicular to the sensitivity beam of the shear probe, we develop double probe correction with two acceleration signals: y and z to eliminate the noise. As a result, the dissipation rates reduce two orders of the magnitude, being consistent with the scaling estimated from the SCS. The turbulent kinetic energy of dissipation rates calculated with data measured by MTMI are from 10^-9 to 10^-4 W/kg.