Autonomous Ocean Turbulence Measurements From a Moored Upwardly Rising Profiler Based on a Buoyancy-Driven Mechanism

Abstract

An autonomous Moored Reciprocating Vertical Profiler (MRVP) has been developed and tested for measuring ocean turbulence. The MRVP is designed to combine the advantages of long-term moored measurements at specified depths with those of short-term ship-supported continuous profiling performed at high vertical resolution. The profiler is programmed to repeat vertical motions autonomously along the mooring cable based on a buoyancy-driven mechanism. A sea trial has been conducted in the South China Sea to evaluate the performance of the profiler. The shear probe data are unreliable when the flow past sensors is not sufficiently greater than an estimate of turbulent velocity. For 65% of the dataset, turbulence measurements are of high quality and the magnitude of dissipation rates is up to O(10−10) W kg−1. To minimize the contamination induced by instrument vibration and improve the estimation of turbulent kinetic energy terms, an advanced cross-spectrum algorithm is implemented to the measured shear data. The corrected spectra agreed well with the empirical Nasmyth spectrum, and dissipation rates had averagely decreased a factor of 2 and 8 times lower than the raw spectra. The autonomous MRVP is proven to be a stable platform, and the novel upward measurement provides a new perspective for measuring long-term time series of turbulence mixing.

An Integrated Spatio-Temporal Features Analysis Approach for Ocean Turbulence Using an Autonomous Vertical Profiler

“…The spatial-temporal properties of turbulent energy cascade were analyzed using the real experimental dataset collected by an autonomous vertical reciprocating profiler (AVRP), which was designed independently by the Ocean University of China, and the detailed mechanical structure and working principles of this AVRP platform have been given in the literature [15]. The deployed moored system (Figure 1) comprises several buoyancy elements, a 38 kHz acoustic doppler current profiler (ADCP), two groups of Sea-Bird Electronics CTD sensors (SBE37SM-RS232, recorded the information about conductivity, temperature and depth), an AVRP instrument, a Doppler current meter (RCM11), two parallel acoustic releases (ARs), and an anchor block [15]. The CTD sensor mainly records the water depth, temperature, and conductivity in the vertical direction.…”

“…The dissipation rate of TKE (ε) is used to describe the energy dissipation in the turbulence mixing and dissipation process. The dissipation rates are denoted as the rate at which turbulent energy flow is irreversibly converted to heat from the largest scales to the smallest scales due to the interactions of molecular friction, which are also proportional to the shear variance that characterizes the intensity of turbulent shear [15]. The vertical distribution of dissipation rates between 600 and 1500 m depth is given in Figure 8.…”

A Multifractal Cascade Model for Energy Evolution and Dissipation in Ocean Turbulence

“…To comprehensively verify the effectiveness of the method, two turbulent datasets measured in horizontal and vertical directions were utilized to examine turbulence properties. Two datasets were collected at two experimental locations in the South China Sea (SCS) [15,16], and the specific coordinate information of the two datasets is exhibited in Figure 1.…”

A New Cross-Platform Instrument for Microstructure Turbulence Measurements

“…Recently, several small mobile platforms have been developed and used to measure ocean turbulence. These include (1) AUVs [4][5][6][7], (2) gliders [8][9][10], and (3) profiling floats [11,12]. These mobile platforms provide highresolution turbulence data with very good temporal and spatial densities in near real time.…”