test for major secondary peaks has been developed and used at CERC. The test 
is applied to the difference in energy density between a spectral peak and the 
preceding and following spectral valleys. If that difference exceeds 3 percent 
of the total of all spectral energy density values, E, then the peak is con- 
sidered major. Details of the procedure with a computerized version are given 
in Thompson (1980). The procedure was applied to the spectrum in Figure 1, com- 
puted from an ocean wave record, and two major peaks were identified. The pro- 
cedure has been applied to 7 station-years of shallow-water spectra by Thompson 
(1980) to show that two-thirds of the ocean and gulf coast spectra have more 
than one major peak. 
If two independent trains have nearly the same frequency but different di- 
rections, they cannot be identified by the method presented in this report. 
However, an analogous method could be developed for use with directional wave 
spectra to identify all wave trains which have distinct frequencies or direc- 
tions. Directional spectra which give estimates of the distribution of wave 
energy density as a function of both frequency and direction are becoming in- 
creasingly available, mainly from spectral hindcasting models but also from 
improved measurement devices. A directional spectrum obtained by the Data Buoy 
Office of the National Oceanic and Atmospheric Administration (NOAA) from an 
experimental large discus buoy (Burdette, Steele, and Trampus, 1978) is shown 
in Figure 7. The figure indicates a concentration of low-frequency wave energy 
coming from the north-northeast and a concentration of high-frequency energy 
coming from the quadrant between east and south. 
Figure 7. Directional spectrum obtained in the Atlantic Ocean 68 miles (110 
kilometers) east of Jacksonville, Florida, at 1900 e.s.t., 30 March 
1977. Contour values are in units of 0.001 meter squared per 
hertz per degree. The radial coordinate is frequency in hertz; the 
azimuthal coordinate is direction from which energy is coming (from 
Burdette, Steele, and Trampus, 1978). 
