Ocean Mesoscale Features Effects On Sound Propagation

Ocean mesoscale features have significant effect on sound propagation . Analyzing mesoscale features effects on sound propagation and determining the general regulation are significant for quickly predicting the sound pressure field in complex ocean environment and inversion the environmental parameters. The effects of oceanic structure variability caused by ocean mesoscale features(such as mesoscale eddies and fronts) on sound propagation are studied and two mesoscale feature oceanic environment models are constructed for analyzing relationship between the characteristic parameters of environmental models and the sound propagation property. Numerical simulation is performed and the result is tested with experiment data. Sound propagation through mesoscale features with a random sound speed fluctuation is analyzed.A numerical experiment of the sound propagation in typical environments in South China Sea are performed by using the parabolic equation model FOR3D code. The ocean environment data comes from the South China Sea assimilation data. The typical propagation cases are sound propagation in deep ocean, through front area, through a seamount, through a declivous path, and through warm eddies. The result shows that a weak front has little effect on the sound propagation , however, the warm eddies can lead to great decrease of propagation lost.By the analysis of the mesoscale features property, a Gauss eddy model and a ocean front model are constructed for simulating the real ocean features. The sound propagation of different sound source frequency through the Gauss eddy model and through the ocean front model of different intensity are calculated. The result shows that the cold eddy decentralizes the convergence zone of the sound pressure field. The warm eddy decreases the propagation loss about lOdB. The eddy effects on low frequency sound propagation is greater than that on high frequency case. The result of sound propagation through a front shows the warm front lends to the shadow zone in a long range after the front, and the propagation loss decreases about lOdB.Based on the Gauss eddy model and the front model, the sensitivity of the characteristic parameters are analyzed, and the result is tested with the data of the sound propagation experiment,, It is shown that the sound propagation through a sound speed field reconstructed by the lsl to 5th orders experiential orthogonal functions(EOF) has an error less than ?dB, that is to say , the 1st to 5th orders EOF are the characteristic parameters.Sound propagation through mesoscale features with a random sound speed fluctuation is analyzed. A statistics theory of normal mode amplitudes in a random ocean is used to analyze the fluctuation of normal mode amplitudes through a mesoscale feature with random sound speed fluctuation. Four kinds of random sound speed fields are calculated. The standard deviation of the fluctuation of normal mode amplitudes satisfies normal distribution in this four cases. The standard deviation of the fluctuation of normal mode amplitudes are different. Variety of sound speed fluctuation along the depth direction has greater effects on the standard deviation of the fluctuation of normal mode amplitudes than variety along range direction.