The range of frequencies considered in the initial MRS analysis of each 

 record is generally comparable to the plotted frequency range. The range is 

 0.131 to 0.214 hertz for South Haven, 0.054 to 0.090 hertz and 0.112 to 0.139 

 hertz for Columbia Light, and 0.052 to 0.226 hertz for South Pass. The spac- 

 ing between analysis frequencies in the initial MRS run was 0.00096 hertz 

 (South Haven), 0.0006 hertz (Columbia Light), and 0.002 hertz (South Pass). 



Deepwater wave steepness, e, can be estimated by using 



e = ak^ 



° (34) 



a = 2ay 



and the dispersion relation governing waves of small steepness 



k = ^21)1 f2 



where 



a = significant wave amplitude 



f = peak spectral frequency 



k = deepwater wave number corresponding to peak frequency f 



g = acceleration due to gravity 



Wave steepness was estimated for each record using a value of fp corre- 

 sponding to the highest peak of harmonics (not grouped into bands) of the FFT 

 spectrum which best matches the times for MRS analysis. FFT spectra are com- 

 puted from 1,024-second records for South Haven and Columbia Light and 819.2- 

 second records for South Pass. Values of e were estimated by equation (34) 

 for South Haven and South Pass. A similar procedure was used to estimate e 

 for Columbia Light except that linear theory was used to estimate shallow- 

 water wave number, k, in place of k in the equation. Although the waves 

 at South Pass are not strictly in deep water, the error induced by using the 

 deepwater wave number is a maximum of about 3 percent. 



Values of a , f p , e, and ef are given with each figure (Figs. 16 to 

 29). The range of frequency covered by ef is positioned graphically in 

 each figure above some high-amplitude constituents. efp is a rough indicator 

 of the frequency spacing between constituents for Columbia Light. For the 

 other two locations, ef spans a large range relative to the frequency spac- 

 ing between constituents. 



A plot of phase (App. A, A-14) versus frequency for each constituent from 

 the South Haven data shows strong evidence of a trend for decreasing phase 

 with increasing frequency (App. D, Fig. D-1) . The phase axis in the figure 

 is stretched to cover several cycles of 360° . This stretching was suggested 

 quite clearly in the data as can be seen by the numerous points included in 

 each 360° cycle. The amplitudes of the constituents were ranked from highest 

 to lowest and the rank is noted beside each point in the figure. Much of the 



49 



