Parameter Definition 



f jpg Peak frequency from the maximum of S(f„) 



T jps (^ 1/fp iFs) peak period from the maximum of 



''' S(fJ 



174. The fourth group contains the characteristic directions of the 

 integrated direction spectrvim. These and their derivatives (spread, asym- 

 metry, and position) characterize the bulk directional properties of a wave 

 field. They are: 



Parameter Definition 



p. IDS 



Peak direction from the maximum of S(^ ) 



^25% IDS Direction at which 25 percent of total energy 



is to the left (or counterclockwise) and 

 75 percent is to the right (clockwise) 



ff^Q^ jpg Direction at which 50 percent of total energy 



is on each side 



^^5^ jpg Direction at which 75 percent of total energy 



is to the left and 25 percent is to the right 



175. The fifth group contains the parameters of the directional 

 distribution function for each frequency in the frequency- direction spectrum. 

 The number of parameters at each frequency is conditional on the number of 

 modes found in the distribution. Basic parameters and characteristic direc- 

 tions are always computed for the whole (180-deg) distribution, independent of 

 any modal definition. They are: 



Parameter Definition 



fjj Frequency at discrete index n 



S(fn) Integrated frequency spectral density at fj, 



g jj Peak direction at frequency f^ 



025% n Direction at which 25 percent of S(f„) is to 



the left 



'50Z,n 



Direction which evenly divides S(f„) 



68 



