Characteristic Line Spectrum Extraction From The Ship-Radiated Noise

Characteristic line spectrum in ship-radiated noise, with hardy intension and stabilization, is produced by reciprocating action of machine assemblies, whirligig, flapping water periodically and revolving vane resonance. So, making scientific researches on characteristic line spectrum is significant for detecting and tracking ship. Vitiated by Ocean ambient noise which exist with pending signals inevitability, moreover, with instrument inherent or artificial cause, there are multiform interferefering noise in receiving signals. Thus, to improve the Signal-to-Noise Ratio (SNR) and achieve line spectrum extracted with high quality, we must think over target and backdrop characteristic roundly, furthermore, adopt appropriate and economical pretreated methods.Considering the non-gauss and non-stationary characteristic of the ship-radiated noise, time-frequency analysis is still the frequently used and effective methods. These methods could describe changes information of the signal in time- frequency field very clearly and intuitionisticly. The law of the low frequency line spectrum transformation is meaningful to detect and track ship. However, there are many discrete line spectrums in modulation spectrum after demodulation management, which can provide more legible structure of line spectrum than power spectrum.Accordingly, considering to the above discussion and to achieve line spectrum extracted with high quality, this paper makes researches as follows:1,Discussed the typical characteristics of the ship-radiated noise and ocean ambient noise.2,Owing to the existence of complicated tendency and strong impulses noises interfering with realistic signals, use the Empirical Mode Decomposition(EMD) to eliminate the complicated tendency and use the morphological filter technique to wipe the strong impulses noises.3,Used typical time-frequency analysis methods to extract low frequency and discrete line spectrum. Besides, take the advantage of the superiority of high-order cumulant to extract line spectrum, which can restrain geoacoustic noise. Also, the high-order cumulant method acquires better effect.4,Combine the wavelet packet decomposition and envelope demodulation measures to extract modulation line spectrum from the ship-radiated noise.