TM No. 377 



Specifically, the device used must measure "both horizontal and vertical 

 velocity components, and thus must contain a coupled system of two speed 

 sensors, one for each component. It is desirable to have a remote recording 

 system that can register the two velocity components simultaneously and 

 quasi-continuously The frequencies of the recorded fluctuations are limited 

 on the upper end by the frequency response of the instrument and on the 

 lower end by the chosen duration of the record, which is governed by the 

 time scale of the fluctuations to be measured. The instrument should have 

 a frequency response that encompasses the highest frequency fluctuations 

 that contribute significantly to the particular phenomena being studied. 



What then are the probable magnitudes of the relevant parameters of the 

 waves in which measurements are to be made? Approximations of the scale 

 of motions can be made by use of classical theory. 



Surface waves may be classified empirically into deep water (short) 

 waves, intermediate waves, and shallow water (long) waves, depending upon 

 the ratio of the depth of the water to the length of the wave. 



Deep water waves occur if 



% > 0-5 : 



(ii-i) 



where D is the water depth and L is the wavelength. Waves that can be 

 described by the ratio 



D 



0.O5 < * < OS (IJ>2) 



are termed intermediate water waves. Shallow water waves are defined by 

 the relation 



L<°'°5. (II „ 3 ) 



Wave measurements were made at the NUWS pier facilities in Narragansett 

 Bay and at the Buzzards Bay Entrance Light Station. The depth of water at 

 the NUWS pier facilities is about 7 meters. The wavelengths, which were 

 measured under relatively high wind conditions, ranged from 3-10 meters. 

 At Buzzards Bay Entrance Light Station the water depth is about 20 meters, 

 and the locally generated wind waves have wavelengths from 10=50 meters. 

 Thus, predominantly deep water waves exist at both locations. During 

 storm and ground swell conditions at the light station, the larger wave- 

 lengths do exceed twice the water .depth; thus, the wave parameters do 

 tend on occasion to satisfy the conditions for intermediate water waves. 

 However, this study is concerned with the properties of wind waves, which 

 are classified, for the most part, as deep water waves. 



The motion of water particles in a deep water wave approximates a 

 circular orbit in which the period of orbital motion is equal to the period 

 of the wave. The orbital diameter is given by 



Do = H e K * : (ii~4) 



15 



