and tested on the RRS "DISCOVERY, the research ship of the National 

 Institute of Oceanography. During the summer of 1953 the Hydrographic 

 Office tested an accelerometer wave gauge mounted on the bow of a 

 ship. The David Taylor Model Basin has successfully tested a raft- 

 like instrument which works on the accelerometer principle. This 

 instrument telemeters the data back to the ship and is expendable. 



Airborne wave measuring techniques have been applied to several 

 problems. One of these problems is the study of the directional 

 properties of the wave spectrum by using photography. However, the 

 work involved in interpreting the many aerial- stereo photographs is 

 immense. Another problem is the study of glitter pattern photographs, 

 as illustrated by the work of Cox and Munk. A glitter pattern is formed 

 ■when the sun is reflected by the ■waves. By using aerial photographs, 

 the glitter pattern can be analyzed to give the distribution of the slopes 

 of the sea surface. Such knowledge provides an independent check on 

 the proposed analytical forms of the wave spectra which have been 

 advanced by Neumann, Roll and Fischer, Darbyshire, et al. The airborne 

 altimeter measures wave heights by indicating the variation of altitude 

 during level flight over the sea surface. This type of instrument is 

 still in the developmental stage; a new model was tested by the Naval 

 Research Laboratory during the spring of I960, and a report on this 

 instrument is expected in the fall of I960. 



Sometimes interest lies mainly in the study of the very low- 

 frequency end of the wave spectrum. Tsunami waves are of this type 

 of low frequency wave. They are practically indiscernible in the open 

 ocean, but, because of their extreme wave length, they can be a hazard 

 when they approach the shoreline and begin to feel bottom. Special 

 recorders have been devised to eliminate the measurement of all but 

 these long period waves in an attempt to provide a warning system. 



The study of small capillary waves, which are artificially generated 

 in the laboratory, requires delicate instrumentation. These waves also 

 have been studied by photographic methods. 



B. DEFINITIONS OF TERMS 



A few of the terms commonly associated with ocean wave instru- 

 ments are presented below. 



1. Bottom pressure fluctuation 



This is the change in pressure at the sea bottom caused by the 

 changing surface wave profile. Bottom pressure instruments can be 



VII- 2 



