In atmospheric acoustics, a flat body of water is often modelled with an infinite surface impedance. However, when the water is rough, the surface responds differently, and an effective surface impedance can be used. This work presents measurements and the use of an effective surface impedance to predict atmospheric acoustic excess attenuation caused by varying sea states. Measurements of the effective surface impedance of rough water associated with sea states 0–3 were performed in the maneuvering and seakeeping basin (MASK) at the Naval Surface Warfare Center, Carderock, Bethesda MD. The ANSI/ASA S1.18 standard is implemented to measure the acoustic response of rough water. Results show that the flow resistivity of a single-parameter model decreases with the increase of the sea state. Measurements performed in a 1:10 scaled spatial domain were used to validate the use of a generalized terrain parabolic equation (GTPE) solver to predict the atmospheric excess attenuation at different locations in the domain. Numerical simulations show that GTPE accurately predicts the effect of sea states. However, when using effective surface impedances, a method previously proposed by the authors outperforms the surface impedance measured via ANSI/ASA standard. Work supported by ONR N00014-23-1-2352, N00014 24-1-2400, N00014-24-1-2437, and N00014-22-1-2492.
Turo et al. (Wed,) studied this question.