Measuring and processing of ocean turbulence from a moored instrument

The process of ocean turbulence mixing generally exists in the ocean. Time series of turbulent fluxes for several months´ duration can serve to understand the role of ocean mixing. In view of this, the Mooring Turbulence Measuring Instrument (MTMI) developed by Ocean University of China (OUC) had been deployed in the South China Sea for about 110 days to obtain long duration data. In this experiment, we have received shear voltage signal, platform vibration data and time series of attitude data. Meanwhile, we analyze these time series in time domain and frequency domain. The results show that the vibration of the platform is the main source of noise in turbulence observation. The motion of the platform determines the low-frequency change of the acceleration signal and the high frequency characteristics of vibration noise are coupling related with each factor. The frequency spectrum indicates that there exists high-energy noise between 5HZ and 8HZ, caused by the vortex-induced vibration. The measured turbulence spectrum is basically consistent with Nasmyth spectrum in the low frequency band. This indicates that our platform can measure relatively accurate shear data. The magnitude of the rate of turbulence dissipation is between 10^-6 and 10^-8, which is consistent with a scaling expected from the South China Sea.