Effects of Ocean Fronts on Underwater Acoustic Propagation in the Shallow Waters Near Hainan Island

This study investigates how ocean fronts affect underwater sound propagation in the shallow waters surrounding Hainan Island. To characterize the regional environment, HYCOM oceanographic fields and ETOPO1 global bathymetry are transformed from geographic coordinates into Lambert conformal conic (LCC) coordinates to construct a regional environmental database. Building on this database, a vertical depth fine interpolation method (VD-FIM) is developed to refine sound-speed profiles and to generate an ocean-acoustic dataset for sound-field simulations. Using this dataset, transmission-loss calculations indicate that seasonal variability, regional circulation, and atmospheric forcing drive strong interactions between cold and warm water masses. These interactions form pronounced fronts that add about 10–20 dB of transmission loss and significantly modify the shallow-water waveguide. In autumn and winter, weaker vertical sound-speed gradients are more favorable for long-range propagation, and sources placed in cold-water masses exhibit improved detection performance at long ranges. Acoustic measurements collected in the South China Sea in November 2023 are consistent with the modeled transmission loss. This consistency indicates that the proposed environmental-modeling and data-processing framework can quantify front-induced acoustic effects and guide the selection of detection periods and source locations. Code for this study is available at GitHub: https://github.com/jxk2026/Hainan-Shallow-Water-Acoustics