may be attributed to the fact that the integrated direction spectrum includes 

 contributions from waves at all frequencies, including those at high frequen- 

 cies. High-frequency waves tend to be less influenced by refraction for a 

 given shoaling propagation path. The effect is to add enough high-frequency 

 energy to the integrated direction spectrum to shift its peak relative to the 

 singular peak of the frequency-direction spectrum. Figure 7 is a good example 

 of this. In Figure 7, the peak of the frequency-direction spectrum is at a 

 low- frequency lobe centered near -30 deg. However, because there is a lot of 

 high-frequency energy at positive angles, the integrated direction spectrum 

 (left rear vertical panel) has a peak near 10 deg. This creates a 40-deg 

 difference in the two measures of peak direction. 



184. The scatter resulting from this type of difference is shown in 

 Figure 12 which is a correlogram of the two measures of peak direction. The 

 diagonal line is the perfect correlation reference. Fewer than 1,046 symbols 

 are visible because both measures of peak direction are discrete. Hence, one 

 symbol location may represent several observations . The figure shows a gross 



90.0 60.0 



30.0 0.0 -30.0 



Figure 12. Correlation of peak directions from integrated 

 direction spectrum and frequency-direction spectrum 



72 



