MARTIN/PERRONE: GEOGRAPHICAL VARIATION OF AMBIENT NOISE IN THE OCEAN 

 FOR THE FREQUENCY RANGE FROM 1 HERTZ TO 5 KILOHERTZ 



10 dB higher than Bermuda, again indicating that the shipping influ- 

 ence is stronger and perhaps of a different character. This differ- 

 ence in character suggests that radiated noise from ships operating 

 in the Bermuda area may differ significantly from those in the 

 Mediterranean Sea; however, in the absence of a quantitative measure 

 of the wind speed effect on noise in the band 10 to 1,000 Hz, it is 

 not possible to assess the validity of that characterization. 



While the curves shown in Figures 2 and 7 indicate very little 

 temporal variation of the data below 100 Hz, data taken in the Labrador 

 Basin over a similarly short time period indicate that variabilities 

 on the order of 10 dB are possible. Figure 8 shows results from 

 several different measurements all taken in a general area of a 

 100 nm square in the central deep water portion of the Labrador Basin 

 400 nm south of Greenland (see MABS site in Figure 15) . The water 

 depth and sound velocity profile shape in this area are similar to 

 those of the Ionian Basin, yielding a large depth excess and a low 

 propagation loss. The area of surface generated noise influence, 

 however, is much more extensive due to the relative sizes of the basins, 

 but the shipping density in the Labrador Basin is at least an order of 

 magnitude less than that in the Ionian Sea. Being that much less and 

 given similar transmission loss properties, the observed levels are 

 also much lower. Also, it is perhaps this very low shipping density 

 which gives rise to the high variability in the data. If only a small 

 number of ships contributes to the noise field at a particular instant 

 of time, then the presence of a few ships more or less can make a 

 large difference in the results. In Figure 8 it should be noted 

 that most of the measurements were obtained over time periods as 

 short as 15 minutes (SONOBUOYS and AUTOBUOYS) . These short periods 

 may contain significant effects due to industrial noise sources (sparkers 

 and air guns) which were prevalent during this time and to different 



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