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

 FOR THE FREQUENCY RANGE FROM 1 HERTZ TO 5 KILOHERTZ 



in establishing the uniqueness of a given area which may be more 

 important to modelers and system designers than level by itself. 

 These descriptors include correlation of ambient noise time series 

 with concurrent wind speed time series and the autocorrelation of 

 the time series, both as functions of frequency. Recent measurements 

 have shown that these other descriptors as well as level versus fre- 

 quency differ in different areas and a rationale has been developed 

 on how these descriptors might help system designers and modelers. 

 In addition, measurements in shipping free areas and at low frequencies 

 indicate that the wind speed generated ambient spectrum may be sig- 

 nificantly different at low frequency than previously conjectured. 



Figure 1 illustrates 1-year time series of ambient noise level 

 in the Bermuda area as observed at the output of several 1/3-octave 

 filters in the range from 10 to 3,000 Hz; the bottom curve is the 

 wind speed time series. 



Figure 2 illustrates the noise spectra for the month of January 

 1966 as reported by Perrone (1969) for one of the deep hydrophones in 

 the Bermuda area for several conditions of wind speed. Each curve 

 represents an ensemble average of several measurements. A special 

 effort was made to eliminate transient noise (biologies, nearby 

 shipping, etc.) from these data prior to processing. The wind speed 

 effect is distinctly pronounced above 100 Hz and below 20 Hz. The 

 measurements were somewhat affected by system noise above 1,500 Hz 

 for the low wind speed conditions and are displayed here as measured 

 and as extrapolated; system noise for higher wind speed conditions 

 at these high frequencies is not a factor in the measurements. A 

 study of these curves indicates that wind speed does not become a 

 dominant factor at this hydrophone until wind exceeds 12 knots and 

 that when it does become dominant the spectra tend to flatten out 



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