Annual average SPL values (63 Hz and 125 Hz 1/3 octave bands as well as wideband) for each single station is reported in Table 1 whereas the average spectra of each of the 12 stations is shown in Fig. 2. An evident increase in the local acoustic energy below 100 Hz was detected once plotting the all the SPLs in the 1/3 octave bands for most of the considered spatial stations, with the exception of two coastal shallow stations (H272 and F363).