four entities displayed: (a) a three-dimensional plot of the surface represent- 

 ing S(f,8), (b) a linear graph of the frequency spectrum S(f), (c) a linear 

 graph of the direction spectrum S(6) (defined below), and (d) a contour plot 

 of S(f,B) . The same vertical scale is used for all three-dimensional plots of 

 S(f,6) within an event, so the relative importance of each observation can be 

 assessed. Prestorm and storm decay conditions thus show low relief, and 

 peak conditions tend to have the largest relief. 



The linear plot of S(f) is shown in the right panel of the three-dimensional 

 box, with its abscissa parallel to the frequency axis of the S(f,6) plot. The 

 direction spectrum S(6) is the directional analog of the frequency spectrum 

 and shows the directional distribution of total energy. Computationally, it is 

 found from 



S(d) = [ Jn S(f,6)df (4) 



and has units of square meters per degree. The analog with S(f) can be seen 

 from the definition of the frequency spectrum as 



S(f) = f " S(f,6)d6 (5) 



J -90 



with units of square meters per Hertz. The left panel of the three-dimensional 

 box contains a linear graph of S(8). Both S(f) and S(6) are drawn to constant 

 scales derived from the maxima of these entities within an event. 



The contour plot of S(f,6) is shown below the three-dimensional box for 

 each observation. Contour intervals are tenths of the maximum value of 

 S(f,0) of all observations in an event. Consequently, spectra having relatively 

 low energy levels have both low relief in the three-dimensional plots and few, 

 if any, lines in corresponding contour plots. Observations with higher energy 

 levels have correspondingly more contour lines. 



Because all four plotted entities within a given event are drawn to constant 

 scales within an event, axis annotation is rather redundant. It is also space 

 consuming. Consequently, axis annotation is drawn only for the upper left- 

 hand set of plots on each page illustrating sequences of S(f,6). Axis annota- 

 tion for all other plot axes within an event is identical. 



Chapter 3 Storm Data 



15 



