Disturbances in noise propagation generated by a moving ship in shallow water

Noise propagation generated by a moving ship in shallow water is always associated with energy loss because of absorption and the fact that sound is scattered by medium inhomogeneities, also resulting in a decrease of sound intensity with range. Furthermore sound propagation is strongly dependent on fluid space geometry and dimension, as well as reflection and transmission loss through the sea bottom. The geometrical dimensions of the measured ship and shallow water are comparable. The depth of water is usually less than the length of the ship, so machinery vibration - due to propulsion machinery and auxiliary machinery - acoustic noise in the compartments below the waterline, flow noise and propeller noise are not generated by the hull of the ship from one point only. Hydroacoustic measurement range is designed with the purpose of exploiting and distinguishing these effects because of the amount of information they each bring; they allow to identify a different class of ship, although interpretation of spatial distribution is very difficult because of sound propagation in shallow water. This paper presents experimental research into the noises of moving ships, measured on the sea bottom, with reflection about the influences of sound propagation on the results of underwater acoustic measurement ranges.