RECENT ADVANCES IN THE CONTROL OF THE IMPACT OF THE UNDERWATER NOISE EMISSIONS BY COMMERCIAL SHIPS

The rising concern about the environmental impact of ship noise on the marine fauna recently pushed national and international bodies to face the problem. In the last decade a few mass strandings of cetaceans due to sea trials of navy sonars (Frantzis (1998)), enforced the interest on noise pollution effects on marine mammals. The problem of evaluating the impact of underwater noise from ships is very complex due to the difficulties in characterising the whole noise chain (source, transmission path, receiver). Standards have been recently issued aimed at the measurement of underwater noise emitted from commercial ships. As regards the transmission path, problems are linked to the correct evaluation of the transmission loss which is influenced by many environmental parameters (water temperature, salinity, pressure, bottom composition etc.) which cannot be easily monitored during measurements. Finally the actual sensibility to noise of the marine mammals it is not completely known, especially for species belonging to the Mysticetes (Baleen Whales). These problems have been analysed in the SILENV collaborative project (Ships oriented Innovative soLutions to rEduce Noise & Vibrations), devoted to the holistic analysis of noise emissions from the ship [radiation inside the ship and outside (in air and in water)]