Frequency — Direction Spectrum. S{f,9) 

 a. Monochromatic, unidirectional 



Frequency — Direction Spectrum, S(f,6l) 

 b. Irregular, unidirectional 



Frequency-Direction Spectrum, S(f,9) 

 c. Monochromatic, directionally spread 



Frequency-Direction Spectrum, S((,d) 

 d. Real sea state 



Figure 2. Examples of frequency, direction, and frequency- 

 direction spectra 



27 



