Ms. Bei Dai Profile

Bei Dai

at China University of Geosciences(Wuhan)

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Publications (2)

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Proceedings Article | 1 November 2021 Paper

Vibration detection and reconstruction based on Φ-OTDR with dual AOM

Bei Dai, Zhihua Yu, Ao Chen, Yutong Li

Proceedings Volume 12057, 120570A (2021) https://doi.org/10.1117/12.2603937

KEYWORDS: Signal detection, Bragg cells, Signal to noise ratio, Heterodyning, Optical fibers, Sensors, Backscatter, Signal processing, Data acquisition

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In the current practical application, the signal of the balance detector in Φ-OTDR system is transmitted at about 100MHz, with the A/D sampling rate is usually above 2GS/s, which requires higher requirements on acquisition equipment and signal processing equipment. The cost and stability of its equipment could not be completed. In order to solve this kind of problem, a phase-sensitive optical time-domain reflectometric (Φ-OTDR) system based on dual AOM which add frequency shift structure for local oscillator light is proposed. This system could obtain the position information and timefrequency characteristics of vibration signal simultaneously under lower sampling frequency by reducing the frequency shift of the backward-scattering Rayleigh light signal. Under the condition of low sampling rate, the initial impulse energy loss is reduced to improve the quantitative analysis ability of disturbance signals. The experimental results show that the spatial resolution of 5m is achieved on the 1.43km sensing fiber, the details of the original backscatter Rayleigh signal could appear as a sinusoidal signal and impulse energy of them is stronger. After noise reduction, the SNR could be increased from 10.37dB to 20.59dB for signal reconstruction with a disturbance frequency of 500Hz. The improvement of the SNR indicates that the Φ-OTDR detection of the dual AOM is feasible and effective in the detection of weak stress signal monitoring at low sampling rate.

Proceedings Article | 1 November 2021 Paper

Obtain the phase velocity of ocean waves by using distributed acoustic sensing

Yutong Li, Zhihua Yu, Ao Chen, Bei Dai

Proceedings Volume 12057, 120570S (2021) https://doi.org/10.1117/12.2604290

KEYWORDS: Phase velocity, Image processing, Edge detection, Wave propagation, Fourier transforms, Seismic sensors, Optical fibers, Acoustics, Data processing, Sensing systems

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In the field of ocean and seismic wave detection, the distributed acoustic sensing based on chirped pulse is used to obtain the specific information of different waves and to dig out the available effective content. But with the huge amount of data, there will be some problems of low computational efficiency and long processing time. This paper applies image processing methods to analyze the phase velocities of different waves. The method combines different technologies to get the related analysis more quickly. Specifically, on the basis of the original data, the two-dimensional Fourier transform processing is performed on the two-dimensional matrix as preprocessing, and then the edge detection algorithm and the operation of color inversion is used to process the data of 20-30 kilometers. After that, all the results are converted into scatter plot form. Then the required scatter points need to be kept and fitted, and this step contributes to obtaining the range of phase velocity variation of different waves through the tangent of the fitted curve. The final result is in line with the phase velocity of the actual situation analysis, and the process is more convenient. The methods proposed in this paper are more convenient to calculate, and they reduce the workload. As a result, they are suitable for monitoring the phase velocity of seismic wave and ocean wave detection.

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