| Abstrakt: |
This report presents a set of 50 source spectra obtained from merchant ships of opportunity near Genova, Italy. The source spectra were calculated from radiated-noise spectra measured on a towed array together with a transmission-loss spectrum computed from a parabolic equation model. The aggregate source spectra are characterized in terms of a mean source spectrum and three source-level histograms computed for different frequency bands. It is shown that the mean spectrum is comparable in level and shape to a spectrum computed from a well-known empirical model and that the source-level histograms are approximately Gaussian with standard deviations of 5, 5.5, and 6.8 dB, respectively. Finally, a sub-sample of 36 spectra is drawn from the aggregate and separated into three identifiable ship classes, namely, passenger/ferries, cargo ships, and tankers. It is seen that the source spectra for the three different ship classes have comparable means and standard deviations. From this result it is conjectured that both the mean spectrum and the source-level histograms are not sensitive to ship class and can therefore be taken as representative of shipping in other regions with different ship class percentages. [ABSTRACT FROM AUTHOR] |
