Research on the evolution mechanism and modeling of ambient noise before and after typhoons.

While ambient noise is strongly correlated with wind speed during typhoons, the lagged response of sea state introduces complexity to the characteristics of wind-generated noise following typhoon passage. Using ambient noise data collected in the South China Sea, this study reveals a two-stage mechanism governing noise evolution across the typhoon life cycle: Ambient noise during the typhoon's active phase is primarily governed by wind speed, whereas noise variability during the decay phase is driven by the combined effect of wind speed and significant wave height. Accordingly, a deep-sea ambient noise model is developed based on whitecap parameterization and ray acoustics theory. Validation results indicate that a single-parameter model using sea surface friction velocity yields reasonable accuracy during the active phase but deviates by up to 20 dB after the typhoon subsides. Under these conditions, the two-parameter model integrating both sea surface friction velocity and significant wave height constrains the prediction deviation to within 7 dB. Finally, acoustic inversion of sea surface whitecap coverage is performed based on the proposed noise model, showing close agreement with the optimized stage-dependent combined model.