Experimental Studies of Underwater and Airborne Noise of Hovercraft in the Ural River Estuary

Abstract

In an ecologically sensitive region—the Ural River Delta Nature Reserve near the Caspian Sea shelf—simultaneous measurements of underwater and airborne noise from a Griffon BHT130 hovercraft were conducted. The measurements were designed to assess the potential negative impact of hovercraft noise on the fish and birds of the reserve. In addition to determining sound pressure levels, a gradient-type vector receiver, formed by four spatially spaced hydrophones, was used to estimate the absolute particle velocity levels of underwater noise. Such measurements are an important part of underwater noise research, as a significant proportion of fish perceive sound as particle vibrations. Simultaneous recording of underwater and airborne noise allowed us to evaluate their mutual correlation. The resulting correlation between the underwater and airborne noise levels from the hovercraft can be used to simplify the estimation of the upper limit of underwater noise based on the measured airborne noise levels. The measured and estimated maximum underwater noise levels of the hovercraft were significantly lower than those of conventional submersible motor-driven vessels, making the hovercraft an attractive alternative for operation in areas with particularly high requirements for permissible levels of anthropogenic noise impact in the aquatic environment.