A study of the effects of given filters upon the two power 
spectra under consideration thus shows that the forecasted values 
would be completely different in many cases for the same storm 
parameters and the same point and time of observation. For many 
forecasts based upon equation (9.50) there would simply be no 
waves present, whereas for the same forecasts based upon figure 
22 (equation 9.52) an appreciable disturbance would be present. 
These two examples therefore make it evident that there is no 
hope for consistently accurate wave forecasts until E5(p 8) has 
been measured for wave systems at the edge of an actual storm at 
sea. Dealing with the significant waves at the edge of the storm 
without regard to the underlying power spectrum can never yield 
consistent results. At this time, the hope that E,( ,©) will 
in some way be a function which depends consistently upon the wind 
velocity, and the air mass in which the winds are blowing so that 
it can be predicted is expressed. Methods for measuring E5( 49) 
will be given in the next chapter. 
Decrease in wave height with travel 
For the same power spectrum at the source (say figure 22), 
the effect of doubling R and top is interesting to study. Filter 
Vetior Cha = 22.5° for example could be reflected in the 6 = 0 
axis. Then it would correspond to the filter for the same para- 
meters given on the figure except 85 would then equal + 22.5°. 
Thus doubling R (or x and y) and t.,, results in a power spectrum 
at the new point of observation with the same value ofp .,, but 
u 
A p and A® are approximately halved. Consequently the potential 
Saas 
