RESULTS 



The effect of ever-increasing areas (approximated by the 

 cumulative wave-height tabulations) over which maximum wave 

 height is considered on the ambient -noise level in the third- 

 octave -band channels at each station is shown in figure 6. With 

 the exception of station C, all stations yielded coefficients of 

 correlation which suggest a noise/wave dependence at frequencies 

 less than about 32 c/s and greater than about 160 c/s. 



An apparent anomaly in the neighborhood of 20 c/s is noted 

 in figure 6. A possible explanation for it is the way the respective 

 seasonal characteristics of sound pressure level in these frequen- 

 cies vary with the seasonal wave-height characteristics. Note in 

 figure 7 that all stations exhibit a significant increase in sound 

 pressure level in the 20-c/s band for the months of September and 

 October. The increase probably results from 20-c/s signals pre- 

 viously reported by Cummings and Thompson 8 . In the areas 

 around station D, for example, the average local wave height de- 

 creases during these months, and thus a negative coeffienct 

 appears that is unusually large compared to the surrounding fre- 

 quencies. The seasonal effect of the predominance of the 20-c/s 

 signal is illustrated in figure 8. No peculiar effect appears at 

 these frequencies at the time of minimum occurrence of the 

 20-c/s signals (May and June). 



Comparable results are yielded for all four stations by the 

 following data sets: 



1. Occurrences for which the value of wave height above 

 the source was less than 3 feet, and 



2. Occurrences for which the value of wave height above 

 the source was less than 3 feet and the value at the 200-nautical- 

 mile range was 3 feet. Station A (fig. 9) is typical. The smallest 

 number of points in any of the computations for data set 1 was 149; 

 for data set 2, 107. The first group shows a general decrease for the 

 coefficients compared to the parent sample (fig. 6) for nearly all 

 frequencies with the smallest decrease in the 16-to-25-c/s region. 



Greatest 1 percent minimum critical value for the four 

 stations is 0. 13. 



13 



