theory provides a basis for considering possible existence of nonindependent 

 spectral energy at discrete frequencies near the main peak in a variety of 

 ocean wave conditions. 



Field data are conspicuously lacking in the published literature on 

 the question of whether spectral components are really independent. The 

 sparcity of field data is not surprising because field data are notoriously 

 difficult and expensive to acquire, especially in relatively deep water. 

 Also, field data are likely to contain free wave energy in addition to any 

 bound energy. However, several notable field studies by Ramamonjiarisoa and 

 Mollo-Christensen (1979) and Kuo, Mitsuyasu, and Masuda (1979b), and labora- 

 tory wind-wave studies by Lake and Yuen (1978) and Mitsuyasu, Kuo, and Masuda 

 (1979) have been published. Among other procedures, these studies made use of 

 spatial gage arrays to evaluate the phase speed of each spectral component. 

 The extent to which phase speed deviates from linear theory and tends toward 

 a constant is an indicator of the nonindependence of the component. These 

 studies have not reached a definitive conclusion, but rather have made the 

 whole question appear more complex and intriguing. 



Although the presence of bound frequency components has clear implications 

 for nonrandom-phase relationships between components, this important charac- 

 teristic of a wave record has apparently never been examined explicitly. 

 Also, the question of whether or not the spectrum has a definite, noncontin- 

 uous structure has received very little attention. A review of pertinent 

 literature is given in Section II. 



Three samples of field data were selected for analysis in this study. All 

 samples represent relatively deepwater cases in which the spectra were single- 

 peaked, indicating that one wave train was dominating the sea surface. The 

 data samples are described in Section III. 



It is contended in this study that previous studies have been self- 

 limiting in the method for computing phase for each spectral component and, 

 in some cases, in the lack of resolution in frequency. This study thus began 

 with the task of developing viable techniques for (a) computing a stable, 

 meaningful value of phase for each important spectral component; and (b) com- 

 puting spectral components with a resolution in frequency sufficient to 

 identify any detailed structure and yet not have a record so long that the 

 assumption of stationarity becomes suspect. The techniques finally adopted 

 involved the use of high resolution fast Fourier transform (FFT) analysis of 

 a record approximately 15 minutes long, followed by the application of a 

 multiple regression screening (MRS) procedure using a comb of frequencies 

 covering the high-energy part of the spectrum and, in some cases, other parts 

 of the spectrum. This study is believed to represent the first use of a 

 multiple regression screening procedure in conjunction with field wave 

 records. The analysis techniques are described in detail in Section IV. 



Wave grouping characteristics in the time series are investigated in this 

 study as a logical and important complement to the detailed study of spectra. 

 However, techniques for investigating wave grouping are not well established. 

 It is necessary to develop and refine techniques for identifying and quantify- 

 ing wave grouping in a time series. The techniques used in this study are 

 described in Section IV. A new parameter indicative of wave grouping is 

 proposed. 



13 



