Research On Time Frequency And Phase Characteristics Of Low Frequency Ocean Ambient Noise

Ocean ambient noise is the background field of the ocean acoustic field.,which is inherent in the ocean,usually regarded as the background interference field,and it will interfere with the performance of underwater equipment.On the contrary,it is an important condition to achieveacoustic concealmentfor the underwater equipment.Meanwhile,exploring the ocean ambient noise characteristics can provide theoretical foundation for suppressing such interference,then improve equipment performance and working distance,and enhance the safety of equipment.Based on the data of South China Sea test,the temporal and frequency characteristics of ocean ambient noise are studied.The temporaldomain correlation and the power spectrum characteristicsof acoustic pressure and velocityare analyzed in the oceanambient noise.The ocean ambient noise can be classified into non-coherent field and coherent field,so that the contribution of various acoustic sources can be separated in the marine environment noise.Researching coherence of the ocean ambient noise can be applied to analyze relationship of the isotropic noise and non-isotropic noise in the ocean ambient noise.The theoretical study shows that in the frequency band which the wind noise is regarded as the main noise source,the ocean noise possesses the horizontal and vertical energy flow.At the same time,theoretical studyverifies principle that total acoustic energy flow deviates from the vertical direction when wind noise is the main effect.The acoustic energy flow of horizontal and vertical direction can be achieved through the frequency domain azimuth spectrum.The study of vector-phasecan be used to analyze whether exists obviousthe anisotropic componentin the oceanambient noise.The trial data in South China Sea analysis show,when the value of the phase spectrum is closed to the constant,the non-isotropic part accounts for the main component.When the value of the phase spectrum distributes randomly,theisotropic part accounts for the main ingredient.The characteristics of marine environmental noise are diverse in different depths.This paperanalyzes the variation of noise characteristics of ocean ambient at different depths.In addition,the characteristics of ocean ambientnoise changes with time,this paperalso analyzes the sound pressure level and the high-order spectral characteristics of ocean ambient noise at the 1/3oct frequency within the whole testing time.Besides,this essay analyzes comparatively the restrict effect of the bispectrumand the cross-bispectrum on the Gaussian noise.