Accurately estimating the bearing of a target with two hydrophones requires knowing the precise distance between them.However,in practice,it is difficult to measure this distance accurately due to the influence of cur...Accurately estimating the bearing of a target with two hydrophones requires knowing the precise distance between them.However,in practice,it is difficult to measure this distance accurately due to the influence of current.To solve this problem,we propose a method for extracting the time-domain Green's function between two points in multi-ship scenarios and for extracting the time-domain waveform arrival structure between two hydrophones in real-time based on long samples of ship radiation noise cross-correlation.Using the cross-correlation function of the radiated noise from any ship located in the end-fire direction of the two hydrophones,we can estimate the distance between the hydrophones in real-time.To verify the accuracy of our estimation,we compare the result of azimuth estimation with the actual azimuth based on the azimuth estimation of a cooperative sound source in the maritime environment.Our experimental results show that the proposed method correctly estimates the distance between two hydrophones that cannot be directly measured and estimates the position of a cooperative sound source 4 km away with an average deviation of less than 1.2°.展开更多
The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry （BOTDR）, where the simplex pulse codes are applied in the sensi...The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry （BOTDR）, where the simplex pulse codes are applied in the sensing system. The time domain signal of every code sequence is collected by the data acquisition card （DAQ）. A shift-averaging technique is applied in the frequency domain for the reason that the local oscillator （LO） in the coherent detection is fix-frequency deviated from the primary source. With the 31-bit simplex code, the signal-to-noise ratio （SNR） has 3.5-dB enhancement with the same single pulse traces, accordant with the theoretical analysis. The frequency fluctuation for simplex codes is 14.01 MHz less than that for a single pulse as to 4-m spatial resolution. The results are believed to be beneficial for the BOTDR performance improvement.展开更多
The corona-generated audible noise(AN)factor is an important consideration in the design and operation of ultrahigh voltage direct current(DC)and alternate current(AC)transmission lines.Due to the differences in disch...The corona-generated audible noise(AN)factor is an important consideration in the design and operation of ultrahigh voltage direct current(DC)and alternate current(AC)transmission lines.Due to the differences in discharge process and corona-generated space charges between the DC and AC corona discharge,the audible noise from DC and AC corona has different characteristics.This paper conducts a series of experiments by measuring the time-domain waveforms of the audible noise from a single corona source under DC and AC voltage.Sound pressure pulses are extracted from a correlation analysis,and then a detailed comparison of the basic characteristics of DC and AC corona-generated AN in time-domain and frequency spectrum is given.Results from this paper stand to contribute to an explanation of existing results in AN measurement and analysis from DC and AC transmission lines.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.62171148)。
文摘Accurately estimating the bearing of a target with two hydrophones requires knowing the precise distance between them.However,in practice,it is difficult to measure this distance accurately due to the influence of current.To solve this problem,we propose a method for extracting the time-domain Green's function between two points in multi-ship scenarios and for extracting the time-domain waveform arrival structure between two hydrophones in real-time based on long samples of ship radiation noise cross-correlation.Using the cross-correlation function of the radiated noise from any ship located in the end-fire direction of the two hydrophones,we can estimate the distance between the hydrophones in real-time.To verify the accuracy of our estimation,we compare the result of azimuth estimation with the actual azimuth based on the azimuth estimation of a cooperative sound source in the maritime environment.Our experimental results show that the proposed method correctly estimates the distance between two hydrophones that cannot be directly measured and estimates the position of a cooperative sound source 4 km away with an average deviation of less than 1.2°.
基金supported by the National High Technology Research and Development Program of China(Grant No.2012AA041203)the National Natural Science Foundation of China(Grant Nos.61377062 and 31201377)+1 种基金the Program of Shanghai Excellent Technical Leaders,China(Grant No.13XD1425400)the Doctorial Fund of Zhengzhou University of Light Industry,China(Grant No.2013BSJJ012)
文摘The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry （BOTDR）, where the simplex pulse codes are applied in the sensing system. The time domain signal of every code sequence is collected by the data acquisition card （DAQ）. A shift-averaging technique is applied in the frequency domain for the reason that the local oscillator （LO） in the coherent detection is fix-frequency deviated from the primary source. With the 31-bit simplex code, the signal-to-noise ratio （SNR） has 3.5-dB enhancement with the same single pulse traces, accordant with the theoretical analysis. The frequency fluctuation for simplex codes is 14.01 MHz less than that for a single pulse as to 4-m spatial resolution. The results are believed to be beneficial for the BOTDR performance improvement.
基金supported by National Basic Research Program of China(973 Program)under Grant 2011CB209402.
文摘The corona-generated audible noise(AN)factor is an important consideration in the design and operation of ultrahigh voltage direct current(DC)and alternate current(AC)transmission lines.Due to the differences in discharge process and corona-generated space charges between the DC and AC corona discharge,the audible noise from DC and AC corona has different characteristics.This paper conducts a series of experiments by measuring the time-domain waveforms of the audible noise from a single corona source under DC and AC voltage.Sound pressure pulses are extracted from a correlation analysis,and then a detailed comparison of the basic characteristics of DC and AC corona-generated AN in time-domain and frequency spectrum is given.Results from this paper stand to contribute to an explanation of existing results in AN measurement and analysis from DC and AC transmission lines.
