^75%, n Direction at which 75 percent of S(f„) is to 



the left 



K Number of modes found at this frequency 



176. If K is greater than one, the distribution at frequency f^ is 

 multimodal. In this case, an additional set of parameters is computed for 

 each of the K modes. They are: 



Parameter Definition 



k Index (count relative to K ) of this mode 



Pn^^ Fraction of S(f„) contained in mode k 



Peak direction within mode k 



9(k) 

 P.n 



i(k) 

 r,n 



Direction which bounds mode k on the left 

 (counterclockwise) side 



'25%, n Direction at which 25 percent of energy in mode 



k is to the left 



'50%,!, Direction which evenly divides the energy in 



mode k 



'75%,n Direction at which 75 percent of energy in mode 



k is to the left 



5(k) 

 s,n 



Direction which bounds mode k on the right 

 (clockwise) side 



177. Note that it is the set of quartile angles (25-, 50-, and 



75 -percent points in the integrated distributions) that is saved rather than 

 the derived parameters (spread A^ , asymmetry A , and position 1 ). This 

 is because the derived parameters are easily computed from the quartile angles 

 and because the quartile angles are more fundamental properties of a distribu- 

 tion. 



178. Once compiled, this rather lengthy collection of parameters can 

 elucidate the directional properties of a set of wave field observations at 

 several levels of detail. The set is not exhaustive but is rather a collec- 

 tion of some obvious properties which are of interest in directional charac- 

 terization. 



69 



