Numerical Investigation of Low-frequency Shipping Noise in the South China Sea

The characteristics of shipping noise greatly affect sonar systems over the continental shelf because of numerous shipping activities. This work investigated the vertical structures of low-frequency shipping noise in the South China Sea (SCS) through numeric calculation. The source level intensities that depend on the shipping distributions were evaluated using automatic identification system data and incorporated with a parabolic equation to build a numeric model. To investigate the vertical structures, we adopted a short vertical array and the superdirectivity method to avoid the inhomogeneity of the noise field and exploit the vertical structures, respectively. The vertical structures in the SCS show that the noise level was strongest near the deep-sea sound axis at approximately 87.5 dB. The vertical correlation length had the same trend as the noise level, which is close to the wavelength at the depth of sound axis. Furthermore, the vertical directionalities with its strength show the great contribution of sound in the upsloping area, leading to a strong peak near the horizontal direction.