Dalei Song

Underwater Color Image Enhancement Using Combining Schemes

Underwater color image processing has received considerable attention in the last few decades for underwater image-based observation. In this article, a novel underwater image enhancement approach using combining schemes is presented. This study aims to improve color correction under nonuniform illumination conditions. The objective of this approach is threefold. First, to correct nonuniform illumination and enhance contrast in the image, homomorphic filtering is used. Second, the color contrast of an image is equalized by a contrast stretching algorithm in red, green and blue (RGB) color space. Finally, the noise amplified after the previous two steps is suppressed by using wavelet domain denoising based on threshold processing. The comparison of experimental results shows that the proposed approach of underwater image enhancement can correct the color imbalance and is especially suitable for processing underwater color images that have nonuniform lighting.

Underwater Man-Made Object Recognition on the Basis of Color and Shape Features

ABSTRACT Hou, G.-J.; Luan, X.; Song, D.-L., and Ma, X.-Y., 2016. Underwater mad-made object recognition on the basis of color and shape features. In complex underwater situations, how to realize object extraction accurately and effectively is the key technology of underwater object recognition. In this paper, the detection and recognition techniques of underwater man-made objects on the basis of color and shape features have been studied in depth. First, the objects of interest in an underwater image are extracted by applying a color-based algorithm. Then an improved two-dimensional Otsu algorithm is utilized for removing the background color noise. To recognize the shape type of a regular object, a robust algorithm based on shape signature is presented. The experimental results show that the proposed approach is effective and robust, such as an acceptable extraction rate (exceeding 80%) of the object of interest, an ideal outcome of background color noise removal, high accurate shape of the objects edge, and a good average recognition rate of shape type (approximately 90%). It proves that this algorithm can accurately settle the problem of object extraction and recognition under different cases of distance, angle, and illumination.

Using an Active Disturbance Rejection Decoupling Control Algorithm to Improve Operational Performance for Underwater Glider Applications

ABSTRACT Song, D.; Guo, T.; Sun, W.; Jiang, Q., and Yang, H., 2018. Using an active disturbance rejection decoupling control algorithm to improve operational performance for underwater glider applications. The underwater glider is a large time-delaying, time-varying, nonlinear, and strong coupling control system that allows for various submarine environmental monitoring applications. To solve the coupling problem between pitch angle and velocity, improve control accuracy, and reduce settling time for energy consumption for the glider, a dynamic surface decoupling control (DSDC) algorithm based on the active disturbance rejection control (ADRC) is described in this paper. By importing the dynamic surface decoupling control law and first-order low-pass filter to improve control precision and reduce the number of calculations, a decoupling algorithm based on ADRC was used to solve the coupled control problem for an underwater glider. Combining the mathematical equation for motion and the kinematic equation for an underwater glider, the DSDC-ADRC algorithm was implanted into the controller. Simulation tests and sea trials showed that it reduced overshoot by 20% and had a 100 s settling time compared with the proportion, integration, and differentiation (PID) algorithm. Sea trials indicated that the decreased overshoot and settling time could save 23% battery energy, which would extend the sail distance 29.9% further than before.

The Design of Ocean Turbulence Measurement with a Free Fall Vertical Profiler

The newly designed instrument Free Fall Vertical Profiler (FFVP) developed by Ocean University of China (OUC) had been deployed in the Western Pacific in March 08, 2017 and succeed to collect turbulence signals about 350-m-deep water. According to the requirements of turbulence measurement, the mechanical design was developed for turbulence platform to achieve stability and good flow tracking. By analysing the Heading, Pitch and Roll, the results suggested that the platform satisfies the requirements of stability. The power spectrum of the cleaned shear signals using the noise correction algorithm match well with the theoretical Nasmyth spectrum and the rate of turbulence dissipation are approximately 10-8 W/kg. In general, the FFVP was rationally designed and provided a good measurement platform for turbulence observation.

Research of an accurate buoyancy adjusting method of underwater glider based on temperature compensation

Underwater glider is developed for the application of marine variables observation by changing the net buoyancy as a driving force. It has many advantages, such as gliding with high efficiency, less power consumption, low noise, no pollution and so on. An accurate buoyancy adjusting method which used for underwater glider based on the volume change of interior gas is introduced in this paper. Besides, the buoyancy adjusting system using this method of the self-developed OUC underwater glider is described in detail. And we obtain the relation among the volume of external bladder, interior gas pressure and temperature by a measurement experiment. Finally, the comparative experiment between the interior calculation and the actual measurement of the volume of external bladder is performed simultaneously. The experimental results show that the buoyancy of glider can be accurately measured by the system, therefore successfully proving the validity of the buoyancy adjusting method.

Quantitative analysis methods of dissipated energy in the ocean turbulence

Turbulent energy cascade and intermittency are very important properties in marine fluid flows and it has become an interesting field in physical oceanography research. To quantitatively characterize that how the turbulent dissipated energy are distributed among the various scales of motion and examine the different physical processes occurring on these different time scales, we propose a quantitative analysis method based on the adaptive empirical mode decomposition, wavelet transform technique and local intermittency measure approach. The energy cascade in the ocean turbulence is investigated using the measured shear data in the South China Sea. These collected long-term turbulence series are used to resolve the critical role of energy cascade and larger-scale ocean circulation dynamics.

Turbulence estimation from simultaneous temperature and velocity shear micro-structure measurements with a free-fall vertical profiler

A free-fall vertical profiler developed by Ocean University of China had been deployed in the South China Sea with the descend speed of 0.35–0.4 m/s. Both of the fast-response thermistor and shear probes are attached to the turbulence observation instrument, which are used to estimate the turbulence intensity. Throughout the observation period, the profiler succeed to collect time series of turbulence shear and temperature fluctuations and this allowed certain issues to be addressed. In this paper, the measured turbulence data are processed and analyzed in time domain and frequency domain. The shear probes are sensitive to the vibration of the platform. So, the measured turbulence data need to be corrected to improve its accuracy. To analysis the effectiveness of the collected data, power spectra of both the velocity shear and temperature gradient are compared with the theoretical spectra, respectively. Dissipation rate of turbulence kinetic energy ε can be directly estimated by integrating the wavenumber spectrum of the observed shear. Furthermore, by fitting the observed temperature gradient variance spectra to the Batchelor theoretical forms, an indirect measurement of εT is obtained. Here, the temperature-derived dissipation rates εT are compared to the shear-derived results ε. The dissipation rates from the above two independent methods agree to within a factor of 10 on average in a wide range of 10−10–10−7 W/kg. Thus, turbulence estimation using free-fall vertical profiler confirmed to be valid, which extends possibility to obtain much more turbulence data in deep and wide oceans.

Research and design of semi-physical motion simulation systemt of buoyancy-driven underwater glider

As buoyancy-driven underwater gliders which have multi-functionality become more and more important instruments of monitoring and exploring the ocean, it is momentous to research and verify the performance of hardware of glider and the function of control software by establishing mathematical model and simulation. So a semi-physical motion simulation system of buoyancy-driven underwater glider is designed in this paper. Not only can this system simulate the underwater performance of glider in a virtual environment, but also it can accomplish the interaction between entity and virtual node using three-dimensional technical display. The semi-physical motion simulation system is used to simulate the behaviors and motions of glider in order to test the software, hardware, data interface and reliability of the glider without launching it into waters. Finally, comparative trials in virtual environment and underwater environment are performed respectively. The result shows that the simulation system can simulate the underwater exploration process of glider satisfactorily with error of maximum depth being less than 2m when maximum depth is set as 120m, and the mathematical models along with simulation algorithm can meet requirement of real-time, therefore successfully proved to be feasible and referential for the design of underwater buoyancy-driven glider.

Measuring and Analysis of Long-Term Turbulence Dissipation in the South China Sea

Measurements for long-term ocean turbulence observation are obtained from a mooring line deployed in the South China Sea. The measurements were made at a single level of 250-m depth in the water column for about three-month duty cycle. We concentrate on the shear velocity measurements and processing. The correlation between the vibration noise and the motion of the platform is analyzed. A multivariate correction procedure is applied to remove vehicle motion and vibration contamination from the estimates of the turbulent kinetic energy (TKE) terms. These time-extended measurements of TKE have yielded a valuable database. Based on advanced spectral methods, the evolution processes of ocean turbulence in the South China Sea are illustrated by the dissipation time series. The distribution patterns of dissipation in different time scales reveal the multiscale evolution and time dependence over the tidal cycle. The extended observations of dissipation will contribute to improving our understanding of the ocean evolution processes in the South China Sea.

Multi-scale analysis of turbulence dissipation in the South China Sea

Measurements for long-term ocean turbulence observation are obtained from a mooring line deployed in the South China Sea. The measurements were made at a single level of 250m depth in the water column for about 3 month duty cycle. These time-extended measurements of TKE have yielded a valuable database. Based on advanced spectral methods for dissipation time series, the evolution processes of ocean turbulence in the South China Sea are illustrated. The distribution patterns of dissipation in different time-scales reveal the multiscale evolution and time dependence over tidal cycle. The extended observations of dissipation will contribute to improving our understanding of the ocean evolution processes of multiple time scales in the South China Sea.