Experimental investigations of underwater and airborne noises produced by a large hovercraft in Ural River estuary

Simultaneous measurements of underwater and airborne noises produced by Griffon Hoverwork BHT130 hovercraft were carried out in environmentally sensitive area - wildlife preserve in the area of the Ural River estuary near the Caspian Sea shelf. Measurements were organized to assess the possible negative impact of noise from hovercraft on fish and birds in wildlife preserve. The particle velocity of underwater noise was estimated by using a gradient-type vector receiver. That was a distinctive aspect of the underwater noise studies since the majority of fish perceives the sound in terms of vibration of particles, and only a few as the pressure. Using synchronous recording of underwater and airborne noises, the mutual correlation of these data was investigated. The obtained correlation levels between underwater and airborne noises produced by hovercraft can be used for simplified estimation of the upper boundary of underwater noise level by measuring levels of airborne noise. The measured and estimated maximal levels of underwater noises of hovercraft are considerably lower than noises from conventional vessels with underwater engines, that makes hovercraft attractive alternative for use in locations with high underwater noise requirements, such as Ural River estuary and Caspian Sea shelf.