where 



a=. "i/raHrv 



This expression is valid for s\ii:'face waves, where theoretically all periods 

 between and OO are possible. To extend this concept to depth it is 

 necessary" to transform the surface power spectrum to a pressure power spec- 

 trum and, considerinf; the filtering action of depth, evaluate the integrals 

 from the cut-off period TsTl. to T= «so • 



First, to reiterate what is meant by a wave period, consider a time- 

 series record of pressure variations on the bottom of a body of water due 

 to the passage of surface vdnd waves o 



To ::=^ > «: T| 



Mean 



The time it takes, for the record to complete a cycle (doT-mcross to dovmcross) 

 is called a period "U (a= o,i,a... .). The average wave period at a given 

 depth (bottom) will be represented by _ ,, 



\-- 



1 





Cn) 



In general, it is not possible to solve this equation analytically, but a 

 numerical solution will be valid* 



The wave measurements represented by figure h were made at a depth of 



18 



