I^= 



(l> Ap 



ApC+)^<^AjoApW<l^ 



u 



f+*^*y «)<&*) 



(11) 



The higher frequencies are essentially damped out due to the filtering 

 action of depth. Therefore, in a pressure record the limits of equation (19) 

 go from to b where b varies according to the depth. Furthermore, 

 from the analysis of power spectra it appears that the lower limit can be 

 chosen also. Thus, in effect the requirements can be fulfilled for an ideal 

 band pass filter whose pass band extends from T■e^, to T^^ • 



5 





i^l-^lY 



00) 



or in terms of T" 



^'5 (TMb*)^ 



Wl) 



Choosing -!-£^ =: .05 > the graph of equation (20) showing R^ for 

 various values of 4-1. is given in figure 9. The choice of -rb is ne- 

 cessarily a function of the pressure recorder and the depth. The choice 

 of -TL with depth is not exact, but since there is probably some maxi- 

 mum amplitude of a wave for a given period, i |-fk » there is some maximum 

 -fu which will be associated with it. This tu maximum is not realistic 

 for a great nany sea conditions, however, and thus the choice of T'Lyy^cJi^ 

 remains a question. 



If not more than two percent of an elemental wave were recorded by a 

 pressure recorder, then using figure 1, the minimum periods to be expected 

 in a pressure record would be as follows: 



24 



