48 Observations and Measurements of Ocean Waves 



greatest number of stereophotogrammetric pictures were taken during the 

 "Meteor" Expedition in 1925-7. To complete these observations, more 

 pictures were taken by the "Deutschland" on two winter cruises in the North 

 Atlantic, and the excellent pictures were discussed, together with the "Meteor" 

 observations, by Schumacher (1939). The discussion includes 17 maps of 

 the "Meteor" Expedition and 13 of the "Deutschland", which have all been 

 published in the results of the "Meteor" Expedition on a scale of 1 : 1000. 

 The contours are at an interval of 20 cm and they show extremely clearly 

 the multitude of forms. Furthermore, from each map there have been selected 

 a number of profiles, which have been added to the discussions. Average 

 waves were computed, which have been obtained by grouping several profiles 

 and by eliminating small irregularities. In this process the wave length was 

 standardized on 25, 50, 100 and 200 m. These average waves constitute an 

 excellent material for the study of wave profiles. Furthermore, we have to 

 mention the stereophotogrammetric pictures taken by Weinblum (1935) 

 on the "San Francisco" in 1934 in the North Atlantic, and the pictures taken 

 on the "Westfalen" in the summer of 1933 which Schumacher (1936, p. 239) 

 published. 



The complete analysis of all maps gives much information on wave lengths 

 and wave heights and on the steepness of waves. All these data have been 

 condensed in Table 8. From this table we can see that with a well-developed 

 sea we often find wave lengths of 150 m and over. It is evident that in earlier 

 days the wave lengths were undervaluated because of the flat wave crests. 

 The concept of wave height has not been clearly established for natural 

 waves, because normally neither two successive troughs nor two successive 

 crests are in the same level. At present we accept as wave height, the average 

 between the wave trough and wave crest at the front and at the rear of the 

 wave. From Table 8 we can derive that as an average the wave height is not 

 too large, most values vary between 3 and 6 m. The largest difference in 

 levels measured by stereophotogrammetry on a picture taken on the "San 

 Francisco" was 18 J m and seems to belong to a wave of 16 m height. We 

 can, therefore, accept Cornish's statement that in many cases waves have 

 exceeded the height of 21 m. 



According to the measurements by Schumacher, the ratio between the 

 wave height and the wave length varies from 1:17-6 to 1:92-2. This value 

 is for a swell near decay. Wind waves values vary from 1 : 19 or 1 :20; waves 

 generated by trade winds from 1:28 to 1:33. Maximum values of 1:10 and 

 more occur, according to Kruemmel (1911, vol. II, p. 82), only for waves 

 in their initial stages; when the waves are older, this ratio becomes smaller 

 and is, then, dependent on the stage of development of the wave. 101 waves 

 measured by Schumacher had the following distribution in percentages: 



h\l = 1 : 20 : 25 : 30 : 35 : 40 : 45 : 50 : 55 : 60 : 65 : 70 

 7 4 15 8 23 19 11 7 4 1 1 



