Influence of acoustic environment on the vertical directionality of ambient noise in coastal water

Abstract

The vertical directionality of acoustic ambient noise has been a subject of much interest in the past. It is a well defined physical quantity that can be measured experimentally with a vertical array. It possesses certain deterministic features that can be modeled theoretically with environmental acoustic and source data. Ambient noise in coastal shallow waters, including its vertical directionality, is not very well known and also difficult to model/predict. This is because the acoustic environment varies with time and is location dependent. Thus arises the question does the vertical directionality of the ambient noise depend on the acoustic environments (found in typical coastal waters)?. The authors note that due to the shallow water depth, sound (noise) propagation can be significantly influenced by the bottom. How much bottom interaction will depend on the sound speed profile in the water column: whether it is downward refractive or not. Bottom attenuation will in turn determine how far the sound will propagate in the water column. Using a modal representation, the authors obtain a closed form expression which can be used to interpret and predict the noise vertical directionality as a function of the environmental acoustic parameters. As the deterministic features of the noise vertical directionality is controlled by the sound propagation in the channel, it could be used as an acoustic indicator of the acoustic environment in the area.