pels trd* 



local sea 



Figure 5. Spectral distribution of wave energy 

 (log-log scale) . 



lines are superimposed, mostly at 1 and 2 cycles per day. 

 There are shallow-water tides at higher harmonics, mostly 

 4 and 6 cycles per day. Then follow seiches and tsunamis 

 with periods ranging from minutes to several hours, and 

 finally wind waves (swell and sea). This continuum cannot 

 be predicted because, although the amplitude may be reason- 

 able estimated, the phase is random. Thus, when we analyze 

 for a particular tidal frequency, we get a vectorial com- 

 bination of the signal and noise. Tide predictions are 

 ordinarily accurate because the signal to noise ratio is 

 large. 



26-12 



