Figure 2. 
Figure 3. 
900 
800 
600 
400 
Energy Density (m*/Hz) 
200 
0 0.05 0.10 0.15 0.20 
Frequency ( Hz ) 
Energy spectra for wave record at 0400 e.s.t., 17 March 
1968, from a weather ship in the North Atlantic, computed 
with different approximations to the autocovariance func- 
tion and different spectral smoothing functions (after 
Wilson, Chakrabarti, and Snider, 1974). 
soos FET used with |.024-second time 
yf series smoothed by cosine bell 
---- Avg. of spectral values computed with 
FFT for eight 128-second time series 
—-— Autocovariance procedure 
me Se 
Relative Energy Density (arbitrary units) 
1/64 1/8 1/4 3/8 1/2 5/8 3/4 7/8 
Frequency (Hz) 
Energy spectra for record composed of three superimposed 
sinusoidal waves. Simulated frequencies indicated by 
vertical lines from top of graph (after Harris 1974). 
10 
