High Signal-to-noise-ratio Target Signal Extraction Method Of Optical Fiber Hydrophone System

With the development of marine science and technology,more and more attention has been paid to the protection,development and utilization of the ocean.Sound waves have the farthest propagation distance in water,which makes underwater sound has become the main carrier of marine information sensing and transmission,and underwater acoustic technology has been widely concerned and studied.Optical fiber hydrophone is a sensor for collecting underwater acoustic signals,it has the advantages of high detection sensitivity and anti-electromagnetic interference,so it has become the main tool to detect underwater sound waves.However,in the complex and changeable ocean background noise,some noise will inevitably be introduced into the transmission,acquisition and even reception of the underwater acoustic signal,which makes the underwater acoustic signal received by the optical fiber hydrophone produce distortion.Therefore,how to denoise underwater acoustic signal effectively is a difficult problem in the field of underwater acoustic signal processing.In order to solve this problem,this paper will study the denoising of fiber bragg grating hydrophone signal based on variational mode decomposition(VMD)method.The specific research work is as follows:Firstly,in order to solve the problem of the drift of the central wavelength of fiber bragg grating(FBG)caused by the change of external temperature,based on the basic characteristics and sensing principle of fiber grating,a sensor with double grating structure based on thin film sensitization is designed in this paper.In order to detect the target signal accurately,the characteristics of underwater acoustic signal measured by double FBG sensing probe are analyzed,and the optical paths of one transmission with one reflection and two reflection fiber grating sensing systems are designed,and the effects of the output spectrum of the two sensing systems and the half peak width of FBG on the output optical power are simulated.Finally,the fiber Bragg grating hydrophone detection system is designed and completed,the experimental results show that the designed fiber grating sensor probe can detect the low frequency sound waves of underwater 100Hz-1000 Hz and detect the intensity of underwater acoustic signals.Secondly,in order to solve the problem of external environmental noise in the process of signal acquisition by hydrophone,a single target underwater acoustic signal denoising method based on the combination of parameter optimization variational mode decomposition and wavelet threshold(GAPSO-VMD-WT)is proposed in this paper.In this method,the energy entropy is selected as the fitness function of the GAPSO algorithm,and the correlation coefficient is introduced to evaluate the correlation between the intrinsic mode components and the original signal,through simulation experiments,it is proved that this method has better denoising effect than CEEMDAN-WT,EEMD-WT,EMD-WT,WT and other methods,and the signal-to-noise ratio is improved by about 14.5d B on average.Then,this paper studies the separation and denoising of multi-target underwater acoustic signals,proposes a method based on parameter optimization quadratic variational mode decomposition and hilbert transform(GAPSO-QVMD-HT),and uses this method to separate and denoise double-target mixed signals and three-target mixed signals,and finally effectively separate and extract the spectrum information of each target signal.Finally,in order to verify the denoising effect of the proposed method on the measured signal of fiber bragg grating,GAPSO-VMD-WT method and GAPSO-QVMD-HT method are applied to the field test respectively.The experimental results show that the GAPSO-VMD-WT method can recover the waveform of the target signal very well,the energy of the signal is almost not lost after denoising,and has a good denoising performance.The GAPSO-QVMDHT method can effectively separate the frequency spectrum of the measured signal from the frequency interval 100 Hz and 50 Hz,and the instantaneous frequency of the signal is clearly presented after secondary VMD decomposition denoising.