  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.
