filters and the lines are given by solid lines for all three filters. 
See the legend at the bottom of the figure. 
The greater the departure of QD from zero the more the filter 
for equation (9.62) departs from the other filters. The approxi- 
mations employed in obtaining the other filters is therefore most 
accurate for small 6p. In addition the original Fresnel filter 
was more accurate for small values of 0). Consequently, these re- 
sults should not be applied too strictly at large angles. 
If the power spectrum given in figure 22 for equation (9.52) 
were to represent the disturbance at the source, then the appli- 
cation of the filters given in figure 26 would result in various 
quite different sea surfaces at the various points and times of 
forecast. There would be a very small disturbance at the point 
and time used to determine the particular filter labeled number I, 
because the power spectrum is identically zero for 9 greater than 
67.5° and very low for © near 67.5°. In contrast for the power 
spectrum given by equation (9.50), the disturbance would be identi- 
cally zero. 
For filter number III, the power spectrum given in figure 22 
would result in considerably higher waves at the point R = 850, 
and @p = 22.5° (corresponding to y = 326, x = 790 km) than at the 
point determined by filter number I. For equation (9.50) and the 
value of K given for equation (9.50) the waves determined by the 
filter at the above point would be considerably lower compared to 
those determined by figure 22 because only the components from 10 
seconds to 7.75 seconds would be present (due to the original 
nature of the power spectrum). 
atoaG) 2 
