the problem at hand, and combine the individual results to estimate 

 response probabilities, as suggested by Hoffman (1974, 1975). 



(2) Spectral Parameters . 



(a) Number of Peaks . It is relatively common in the ocean 

 for two or more independent wave trains with different frequency and 

 direction to occur simultaneously (e.g., Harris, 1972; McClenan and 

 Harris, 1975; Ochi and Hubble, 1976; Thompson, 1977). The marine sur- 

 face observation reporting code even includes provisions for reporting 

 major secondary wave trains observed visually. Certainly, the concept 

 of a simple, single-peaked spectriom is misleading in many ocean wave 

 records. Yet, there is a lack of reliable quantitative information as 

 to how often major secondary trains occur and how much energy they 

 contain. 



To investigate the occurrence of multiple wave trains, a computer 

 routine was adapted for use in identifying major spectral peaks. The 

 routine (described in App. D) smoothes over spectral peaks and valleys 

 which differ in energy density by less than 3 percent of the total 

 energy in the spectrum. Examples of individual spectra were shown in 

 Figure 5. The major peaks identified in each case by the computer rou- 

 tine are marked with asterisks. 



A fraction of the spectral energy is assigned to each major spectral 

 peak by a simple method. The spectrum is partitioned at the lowest point 

 between successive major peaks (Fig. 7). All spectral energy within the 

 partition for a peak is assigned to that peak. The energy is expressed 

 as a dimensional quantity and as a fraction of the total spectral energy. 



10,000 



8,000 



J 6,000 



4,000 



2,000 



^ Energy in Peck 1 

 ^ Energy in Peak 2 

 '^ Energy in Peck 5 



Peck 1 



Peck 3 



.^^^: 



0.0 



Figure 7. 



0.1 



0.2 0.3 



Frequency (Hz) 



Technique for partitioning spectral energy 

 and assigning the energy to major peaks. 



26 



