cumulative wave heights at increasing areas surrounding the 

 hydrophone, were computed. General trends in dependence of 

 noise levels for particular frequencies on varying areas of storm 

 magnitude may be detected in this way. 



One of the salient problems associated with the study is the 

 possible overlap of the effect of storm activity at the various 

 ranges. For this reason, an effort was made to study the effect 

 of distant changes in wave height corresponding to times when 

 wave height nearby was relatively constant and small. The most 

 frequently occurring waves above the hydrophone were less than 

 3 feet, and one grouping was designed to observe only the times 

 for which the area had this sea state. Subsequent examination 

 showed that the most frequently occurring sea state at 200 nautical 

 miles was 3 feet. A second sort, made to include only times for 

 which the sea state was constant over the hydrophone (less than 

 3 feet) and at the 200-nautical-mile range (3 feet), enabled better 

 judgment from the correlation coefficients of the effect of distant 

 wave fluctuation on ambient -noise level. 



A property of the maximum wave heights recorded from the 

 contour charts further compounded the aforementioned problems. 

 The validity of the correlation tests is subject to further question 

 as a few of the wave-height distributions were not normal. Note 

 in figure 5 the extremely skewed curves for the wave heights at the 

 source and at the 200-nautical-mile range. With further increases 

 in distance from the shoreline the distributions begin to take on a 

 more normal form. 



The correlation between ambient sea noise in the low- 

 frequency range and local storm activity was further explored 

 with data from an automatic weather buoy associated with CNO 

 Project DS/200. The data were compared with third-octave -band 

 ambient-noise data at station D by means of the correlation coef- 

 ficient and by grouping the noise data to correspond to sets of wind 

 data that fell within certain Beaufort groupings. 



Simple sums — the value at the source plus the maximum 

 value at 200 nautical miles, the preceding plus the maximum 

 value at 400 nautical miles, and so on. 



11 



