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Description
Environmental sound propagation over water is usually modelled by treating the surface as acoustically hard and, perhaps more importantly, stationary. This simplification does not account for the possible influence of surface motion on the coherence of the surface-reflected sound field. In these tests, surface motion was generated using a simple ripple-making system in an outdoor shallow-water basin, allowing a range of ripple states to be produced. While maintaining a fixed acoustic source--receiver geometry, transfer-function (TF) measurements above the water surface were used to identify changes in the reflected sound field. For each measurement, water-surface activity was characterised by approximate ripple height and wavelength. The results showed that increasing water-surface activity deepened the incoherence around sensitive frequency bands associated with the source--receiver geometry.