Research on acoustic transmission loss in deep-sea complex environments based on coupled normal mode model

Abstract Deep-sea exploration holds multidimensional significance for the development of human society, encompassing fields such as resource exploitation, earth evolution, and ecological conservation. Addressing the complexity of submarine environments, a 3D high-fidelity topographic model of a 3,000-meter-deep area in the South China Sea was constructed using GEBCO global bathymetric data with a resolution of 15 arc-seconds (approximately 450 m), capable of realistically reflecting intricate seafloor structures. Meanwhile, typical 2D cross-sections were selected, and based on the Kraken coupled normal-mode model, investigations were conducted on several types of typical deep-sea sediments (e.g., coarse sand, sandy mud, and clayey silt). Additionally, an analysis was performed on the acoustic propagation characteristics of two dominant modes in deep-sea environments (Deep Sound Channel and Convergence Zone). The results demonstrate that increasing source depth markedly drives a transition in propagation mode from the Convergence Zone to the Deep Sound Channel, a process governed by vertical gradients in sound speed profiles. Sediment type exhibits significant gradient-dependent effects on transmission loss, with ascending transmission losses observed across coarse sand, sandy mud, and clayey silt substrates. These effects synergistically modulate acoustic propagation alongside source depth variability. This study provides novel insights for deep-sea terrain modeling and serves as a valuable reference for acoustic propagation research in complex topographical settings.