Observations and Measurements of Ocean Waves 



33 



Direction of travel 



10 



20 

 30 

 40 

 50 

 60 

 70 



-1-5 -1-0 -0-5 0-5 10 1-5 2 2-5 

 Velocity of moss transport, cm/sec 



3-0 



Fig. 19. Relationship between velocity of water transport and depth when depth of water 

 is 75 cm (wave tank experiments). 



Considering the difficulty in determining this velocity, we can say that 

 there is a satisfactory agreement between the theory and observations. But 

 this agreement does not necessarily apply to large waves generated by the 

 wind upon the ocean surface in respect to their length, period and velocity. 

 We have to consider, in addition, that the height of the wave and the length 

 of the crest are important factors not to be neglected in ocean waves. 



2. Observation and Measurement of Ocean Waves 



It is relatively simple to observe ocean waves from aboard a ship. Such 

 observation are almost without any exceptions limited to the determination 

 of the velocity c, the wave length I and the period T. In most cases, these 

 observations are based on evaluation or on measuring by means of simple 

 instruments and, consequently, they are subject to numerous sources of errors. 

 This is particularly true for the determination of the wave height. Only 

 recently stereophotogrammetric observations of waves, and especially of wave 

 profiles, have given reliable observations. The results of this new method 

 will be discussed in a subsequent chapter, and we will first deal with direct 

 visual observations. 



Amongst the numerous scientific observations of ocean waves, which 

 were gathered in a systematic manner during oceanographical expeditions, 

 those made by Cornish deserve special attention. Another comprehensive 

 study of waves was given by Larisch-Monich (1925) in a monograph titled 

 Sturmsee und Brandung. His method of work is wave photography. By means 

 of excellent photographic pictures, giving all kinds of phases in wave de- 

 velopment, he has attempted to explain the complex mechanism of wave 



