Modeling of spatial correlation characteristics of broadband ocean ambient noise vector field

Abstract

The signal-to-noise ratio gain of the array is closely related to the spatial characteristics of the noise field. The modeling of the spatial characteristics of marine environmental noise is always a hot spot. For sonar with different functions, the working frequency band and bandwidth are usually different. Therefore, the spatial correlation coefficient of the noise field in arbitrary frequency band has important reference value for designing sonar systems. According to the process of generating the marine environmental noise field under the high frequency approximation condition, a noise field time-domain modeling method is proposed, and the integral expression of the time-domain sound pressure and particle vibration velocity of marine environmental noise in a horizontally layered medium is given. This lays the foundation for establishing a broadband model of the noise vector field. In particular, the analytical expression of the spatial correlation coefficient of the broadband white noise vector field in the vertical direction under specific condition is also given. Following the spectral structure of wind-generated noise, the spatial correlation coefficients of noise fields with different frequency bands and different spectral slopes are numerically calculated, revealing the influence of bandwidth and spectral structure on the spatial characteristics of marine environmental noise, and the principle behind the result is explained through theoretical derivation. With the increase of the array element spacing and bandwidth, the number of oscillation periods and the oscillation amplitude of the spatial correlation coefficient of each component of the noise vector field gradually decrease, which is caused by the frequency domain average of the noise field correlation coefficient. When the spectral slope is less than zero, the low-frequency noise plays a major role, causing the spatial correlation radius of the broadband noise field to be larger than that of the narrowband noise field. The result of the experiment conducted in South China Sea shows that the measured vertical spatial correlation coefficient of the sound pressure field of marine environmental noise is in good agreement with the theoretical result. The model has potential application prospects for the research of transducer array technology and the inversion of environmental parameters.