Characterization of floating offshore wind turbine noise propagation and its contribution to underwater ambient noise levels

The global expansion of floating offshore wind turbines (FOWTs) introduces new sources of persistent low-frequency underwater noise into the marine environment. While operational noise from conventional bottom-fixed turbines is generally considered to have a limited impact, FOWTs are typically deployed at greater depths, where their radiated noise can interact more directly with acoustic propagation channels. This study examines the propagation characteristics of operational noise from FOWTs and its contribution to spatial variations in ambient noise levels through quantitative modeling and analysis. Near-field source modeling was conducted using a finite element method (FEM), with acoustic loading informed by turbine source levels and spectral features reported in recent literature. Frequency-domain representations revealed low-frequency components below 100 Hz. For long-range propagation, a modified parabolic equation (MMPE) model was used with seasonal sound speed profiles (SSPs) from oceanographic datasets. Estimated ambient noise levels, based on Wenz curves and field data, were used to assess the distance over which turbine noise remains distinguishable. Results show that FOWT noise can elevate ambient levels over considerable ranges and may impact acoustic detection and passive sonar performance in certain marine environments.