40 



ro 



20 



£ 

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Atlontic City 

 1037 Cases 



Virginia 

 Beoch 



Nogs Head 

 945 Coses 



Lake Worth 

 962 Cases 



M:chigan City 

 Buoy 



Michigan City 

 Pressure 



Huntington 

 Beach 



Pt Mugu 

 799 Coses 



Presque Isle 

 Pressure 



Noples 

 866 Coses 



1234512345612345 

 Number of Mojor Spectral Peoks 



Figure 17. Percentage of spectra versus 



number of major spectral peaks. 



At the remaining ocean location (Pt. Mugu) only 5 percent of the spectra 

 were single peaked. The infrequency of single-peaked spectra at Pt. Mugu 

 may be attributed both to common simultaneous occurrence of sea and swell 

 waves and to pressure-compensation effects on the spectrum which often 

 make the high-frequency end of the spectrum look like a meaningful peak. 

 At all ocean locations, about one-half the spectra are double peaked with 

 the rest containing three, four, and in a few cases, five major peaks. 

 Several spectra with five major peaks and corresponding pen-and-ink 

 traces are shown in Figure 18. 



Single-peaked spectra are more common for the gulf and Great Lakes 

 sites than for the ocean sites (see Fig. 17). About 40 percent of the 

 Naples spectra and about one-half of the Great Lakes spectra from accel- 

 erometer buoys 6 kilometers offshore were single peaked. Spectra from 

 the Great Lakes nearshore pressure gages show that only 20 to 30 percent 

 of the cases are single peaked. However, these percentages are consid- 

 ered low because the pressure-compensation procedure often creates a 



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