IV. INTERPRETATION OF SPECTRA 
Because of natural vartabtlity tn the spectrum and artifictal variability 
tnduced by analysts and display techniques, the spectrum should never be in- 
terpreted as an exact representation of energy density versus frequency for a 
wave fteld. However, certain major features of the spectrum are consistent 
and meaningful. 
1. Highest Spectral Peak. 
a. Frequency and Period. Frequency corresponding to the highest spectral 
peak, f,, is usually a reliable measure of the dominant wave frequency; fp 
is shown in Figure 1. Period corresponding to the highest spectral peak, Tp, 
is equal to the reciprocal of fp and is usually a good estimate of the domi- 
nant wave period. 
b. Energy and Significant Wave Height. Energy contained in the highest 
peak, Spl> is defined as the total energy in the vicinity of the highest peak. 
Ko 
Lae Ej; (Af); (3) 
; oe : : 
S 
where K, and Ky are indices representing the lower and upper bounds of the 
main peak. The upper and lower bounds sometimes represent a broad range of 
frequencies (see Fig. 1). Spl is relatively consistent, and is less influenced 
than the magnitude of the highest peak by data collection procedures, by analy- 
sis and summarization procedures, and by temporal and spatial variation. 
Some spectral analysis procedures are designed so that (Af); = Af isa 
constant for all j, which leads to 
Lp 3a 
Sol = (Af) ) By oe 
j=K +1 
Significant wave height corresponding to highest spectral peak Hg), is an 
estimate of the significant height for the wave train represented by the highest 
spectral peak. It is computed by the relationship 
Hs1 = 4VSp1 (4) 
Energy density at the highest spectral peak, Emgxz, can be an indicator of 
how well focused the wave energy is in frequency. Although this parameter is 
variable, major differences in Emg, (on the order of 50 percent) between 
spectra analyzed by the same method can be meaningful. Emgqr, is shown in 
Eaooremle 
2. Major Secondary Spectral Peaks. 
a. Identification of Major Secondary Peaks. Major secondary spectral peaks 
are often indicative of independent secondary wave trains characterized by dif- 
ferent heights, periods, and directions than the train represented by the main 
peak (examples are given in McClenan and Harris, 1975). Identification of major 
secondary spectral peaks involves some subjective judgment, but an objective 
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