Spatial Correlation Of Ambient Noise In Northern South China Sea

The spatial correlation of ambient noise field is studied by processing the ocean ambient noise data acquired by ASIAEX 2001(Asian Seas International Acoustic Experiment,2001)in northern South China Sea.Firstly,the vertical directivity,the noise power spectral density and spatial correlation coefficient are calculated to investigate the spatial correlation characteristics of ocean ambient noise affected by distant ships and near ships.The noise of distant ship and near ship have different influences on spatial correlation characteristics of ocean ambient noise.The noise of distant ship led to a high correlation when the separation distance between elements is less than 30 metres of ocean ambient noise below 200 Hz,while it had hardly any impact on spatial correlation when the separation distance between elements is more than 15 metres of ocean ambient noise above 200Hz;the noise of near ship led to oscillation of spatial correlation curve of ocean ambient noise below 800 Hz.The first zero point of spatial correlation coefficient appears when the acoustic path difference approximates to a quarter of wave length of the noise signal with corresponding frequency,while the spatial correlation of ocean ambient noise above 500 Hz was improved.By discussing the acoustic characteristics of noise fields produced by distant and near ships respectively,the spatial correlation characteristics of two kinds of noise fields are reasonably explained.Secondly,the normal mode model of the wind-generated ambient noise field in shallow sea is studied by processing the ocean ambient noise data which is not influenced by noise from near ship.The numerical simulation results,which calculate the spatial correlation characteristics of wind-generated ambient noise field in shallow sea,are compared with the field data.The results show that the spatial correlation characteristics of ambient noise field by this model is roughly consistent with spatial correlation characteristics of low-frequency ambient noise field.However some differences exist for the spatial correlation characteristics of high-frequency ambient noise field in shallow sea,indicating that this model can explain the spatial correlation characteristics of low-frequency ambient noise field in shallow sea.