65 - 



14. Frequency Bands of Greatest Energy 



The block-averaged frequency bands of maximum energy are then 

 identified from one of the operative channels (generally the 

 absolute) and the amount by which each exceeds the average energy in 

 the spectrum is calculated. The truncated Fourier series directional 

 spectrum (Equation 4. 14) is then calculated for each of these high 

 energy bands. The direction of peak energy for each spectrum is 

 reported as that band's direction of wave propagation — adjusted 

 accordingly to instrument orientation relative to true north. 



The "mean direction" of each band can also be calculated as: 



n n 



where n=l,2,3. (If no water surface curvature terms are developed, 

 then n=l,2.) There exists a directional ambiguity for n>l since there 

 exists more than one peak in sin n8 for n>l (from which the bn terms 

 are developed) . 



Since the ultimate intent of the DPG as a tool is to report 



predominant wave characteristics at the installation site, the 



presentation of wave information at the dominant energy levels is 

 considered to be the preferred data display. 



