On site propagation loss measurements through non-impulsive signal deconvolution

The recent concern about the impact of underwater noise emitted by ships, pushed national and international bodies to face the problem of setting limits to ship noise emission. In order to set new limits, a deep knowledge of the three elements of the noise chain (i.e. source, transmission path and receiver) is needed. In this context it is therefore important to measure the acoustic signature of a ship, in order to characterize it as noise source. To this aim, dedicated measurements may be carried out during sea trials, which usually takes place in an area close to the building shipyard. The measurement layout foresees a series of hydrophones deployed in the water column placed at a distance of a hundred metres from the ship that passes abeam the hydrophones on a straight course. Such far field measurements are to be referred to the reference distance of 1 metre in order to ensure results comparability. Sound propagation from the ship to the hydrophones is therefore to be carefully taken into account also considering the fact that measurements are carried out in a continuously changing environment. In the present paper, an experimental technique to characterise the environment frequency response function is presented together with results of its onsite application.