

ir 



§3_ 

 r 3 «; 



0800 0900 



1200 1300 1400 



Ship's Time 



Figure 4 - Illustrative Example of Procedure Used to Average Visual Observations 



Note plotted points are averages of values estimated by seven aerologists on USS VALLEY 

 FORGE for 12 October 1955. 



both the Weather Bureau and the Hydrographic Office for observers are essentially the same. 



Throughout this report the term "characteristic height" will be used to denote the aver- 

 age height of the higher, well-defined waves. The statement in italics will serve as a defini- 

 tion of characteristic wave height. The term "significant wave height" will be used only in 

 its statistical sense. The "characteristic wave period" is the average period of the higher 

 well-defined waves. The characteristic values may be estimated by shipboard observers, or 

 they may be obtained by more precise measurements from stereograms or wave records. 



SEA SURFACE PROFILES 



Sea surface profiles were developed from the stereophotographs by means of planigraphs 

 at the U.S. Naval Photographic Interpretation Center and at the U.S. Navy Hydrographic Office; 

 see Appendix A. Then all profiles were analyzed at the Hydrographic Office by statistical 

 methods as outlined in Appendix A. These analyses resulted in histograms of wave heights 

 and wave lengths as well as in "significant" wave heights. The significant wave heights 

 are listed in Table 4. Only waves of length greater than a certain "cutoff" length were in- 

 cluded in the histograms. The cutoff length is a function of the wind conditions that gener- 

 ated the sea. See Appendix A for an explanation of how the cutoff length was determined. 



The sea surface profiles were later used to determine the characteristic wave height 

 by following the same general procedure as that used by the shipboard observers in making 

 their estimates; thus these two independent determinations of characteristic wave height should 

 be comparable. 



