Funke and Mansard (1979) used the approach to define a single parameter 

 indicative of the extent of wave grouping in a record. Although the Funke- 

 Mansard grouping parameter appears to be effective, a new grouping parameter 

 is proposed in the present study based on Sedivy's (1978) approach to studying 

 wave groups. The grouping parameter proposed in Section IV is similar to the 

 Funke-Mansard parameter in practice but it avoids the need for a rather arbi- 

 trary smoothing function included in the Funke-Mansard parameter. It also 

 avoids distortion of the spectrum which may be caused by high frequencies, 

 formed in squaring the record, aliasing into low frequencies. 



Attempts to relate the narrowness of the spectrum to wave grouping charac- 

 teristics in field records have met with limited success. Houmb and Overvik 

 (1977) observed an increase in the autocorrelation between successive wave 

 heights as spectral width decreased. Rye (1974) reported more pronounced wave 

 grouping in a decaying sea. However, Goda (1976) showed inconclusive compari- 

 sons of spectral width and wave grouping, and Burcharth (1980) reported no 

 observable relationship. Burcharth also reported considerable short-term 

 variability in wave grouping characteristics. Johnson and Ploeg (1977), 

 Johnson, Mansard, and Ploeg (1978), and Funke and Mansard (1979) discussed the 

 possibility that phase as well as energy of the spectral components may be 

 important in determining wave group characteristics. Rye (1979) concluded 

 after a fairly extensive review that the question of how the spectrum is 

 related to field wave grouping characteristics remains unanswered. 



III. FIELD WAVE DATA 



Three samples of field wave data were selected for analysis. The follow- 

 ing criteria for an ideal data sample were designed to optimize the chance 

 that the hypotheses in Section I would be recognizably true: 



(1) Deep water. 



(2) Availability of continuous wave records. 



(3) Stable or slowly increasing significant wave height. 



(4) Relatively high steep waves. 



(5) Relatively unidirectional wave field (absence of secondary 

 wave trains from other directions). , 



(6) Availability of data from at least two sites which are within 

 about 1 kilometer of each other in a line parallel to the direction 

 of wave travel. 



(7) Direct measurement of water surface. 



Most of these specifications for optimum field wave data were also indicated 

 by Lake and Yuen (1978). 



The three gage sites selected are summarized in Table 1, which includes 

 location, gage type, water depth, length of record, interval between records, 

 and time between data points. The gage sites are illustrated in Figures 1, 2, 

 and 3. The history of significant wave height and peak spectral period during 

 the samples is shown in Figures 4, 5, and 6. Peak periods are derived from 



20 



