Cross-Spectral Density Sensitivity Kernels in Surface Noise Field

The main factors affecting the spatial characteristics of surface noise fields are changes in sound speed and sea surface boundary perturbations due to mesoscale ocean phenomena and wind-induced noise, respectively. This study derived the surface noise cross-spectral density sensitivity kernel for sound speed changes and local boundary perturbations and analyzed their effects on cross-spectral density. Numerical results show that the sound speed perturbations of any position in the entire observation plane changes the surface noise cross-spectral density function in surface noise with finite frequency. The cross-spectral density between two receivers in the vertical direction is the most sensitive to the sound speed changes of the region between two receivers. Additionally, the influence depends on the relationship between the wavelength of sound wave and the distance of two receivers. Scattering on the surface boundary perturbation would lead to fluctuations in the cross-spectral density function. When the boundary perturbation along the horizontal direction is distant from two receivers, the cross-spectral density sensitivity kernel for surface scattering oscillates, and the influence of boundary perturbation on the cross-spectral density function gradually weakens. Finally, the period of the cross-spectral density sensitivity kernel oscillations is a half wavelength of the sound wave.