TM No. 377 



A simple amplifier-converter system is being designed to accept raw voltage 

 pulse signals from the wave meters and to convert this data directly into a 

 series of ^"f values., recording them on binary digital tape. This will eliminate 

 tape reading and many sources of error. The digital tape can be fed directly 

 into a computer for analysis. 



Note : A project to study wind and wave turbulence is being conducted jointly 

 by the NUWS Oceanographic Branch and the M.I.T. Department of Meteorology. 

 Field measurements are being made using vertical arrays of lightweight fast- 

 response anemometers aboard the BBELS. Since the output of the ducted meters 

 is similar to that of common cup anemometers , this magnetic tape conversion 

 system will, hopefully., be adaptable to the anemometer system output for 

 stationary time series studies 



Conclusions from Actual Wave Observations 



« 



The majority of the wave observations were made aboard the Buzzards Bay 

 Entrance Light Station (BBELS ). This facility proved highly successful as a 

 platform from which to make the wind and wave observations. 



Gross environmental measurements were made and reported of water temperature, 

 winds, tidal height, and tidal currents to insure a basic understanding of the 

 background from which to study the wind waves. This background information should 

 also prove helpful to others who may wish to use the BBELS for similar or related 

 studies o The following is a brief summary and interpretation of the results 

 obtained with the wave meters „ 



1. The OMDUM III system produced realistic wave velocity patterns. However, 

 the amplitude of the horizontal oscillatory velocity appeared damped, possibly 

 caused by non-rigid instrument mounting. The LIMDUM I system depicted wave 

 velocities showing quasi ^exponential damped motion as a function of depth. 



2. Histogram sorts of the equi-time spaced vertical particle velocities 

 for several records showed an approximate Gaussian pattern, but with a bi -modal 

 tendency. This effect was attributed to the detectable threshold velocity of 

 the wave meter ^ 



3 a The variances Ou. 1 and J^ 1 showed consistent exponential attenuation 

 with depth, but not as rapidly as the exponential decrease of an ideal trochoidal 

 wave system. 



k e Integration of ^PU-' 2 and ^ ?io |V with depth gives a theoretical represen- 

 tation of the oscillatory kinetic energy of the wave motions. These values were 

 found to be comparable to the estimated potential energy of the observed waves 

 derived from wave height estimates. 



5» The auto-spectra of wave motions display spectral peaks at the observed 

 frequencies of the waves. The depth attenuation of wave motions is vividly por- 

 trayed in the auto-spectra as a gross decrease in energy and as a peak shift to 

 lower frequencies, the latter associated with a hydrostatic filtering of 



16k 



