TM No. 377 



from 3 to k meter depths. Above 1000 mcps, the curves (except for U.O m i) remain 

 "between 0.2 to 0.8 cm^ sec -1 . The w spectra curves, however, continue to decrease 

 beyond 1000 mcps. 



The corresponding spectral curves for both sets of observations (A and B) show 

 strong similarities. The gross differences between the curves of c£>y_ and ^^ 

 are also similar in each case. The similarities in the spectra indicate the degree 

 of stationarity of the statistics of the observed motions during the sampling 

 period, whereas the consistent reproduction of the dissimilarities between the w 

 and u spectra indicates the inherent precision (or repeatability) of the wave 

 meters - even though these dissimilarities may be partly caused by the wave meters 

 themselves. 



BBELS-7 Observations - The set of observations designated as BBELS-7 was made 

 using the 0MDUM II wave meter. An additional guy leading from the meter support 

 rod back to a point in the center of the tower was utilized in an attempt to gain 

 horizontal stability. This new pyramidal configuration (see figure IV- 17) was 

 used in conjunction with a heavier (25 kgm) counterweight, giving this system more 

 horizontal and vertical stability than that for BBELS-5 measurements. 



Unfortunately, this series of observations (of u and w at various depths) was 

 made over a 6-hour period. Thus, even though wind conditions remained fairly 

 constant at 6-8 m sec -1 from the SSW, it is difficult to assess the degree of 

 stationarity over so long a period. 



The results of the statistical analysis of the data are summarized in the 

 table IV-3. The distribution of the variances of the vertical velocity component 

 with depth is shown as circles in figure V-20. They were placed along with the 

 data from BBELS-5 because the wind and sea state values were roughly equivalent. 

 Indeed, both sets of data form a relatively narrow envelope. 



The values of Qui 2 " are generally 2 to 5 times larger than C3CC 2 " ; however, _ 

 the difference in these values is not so great as with BBELS-5. The values of U 

 range from -25.7 cm sec"-'- at about 102^4- hours to 0.3 cm sec-1 around 1^20 hours. 

 There are also a few disturbingly large values for w; namely, at 0.5 m I, 10.0 m 

 III, 8.0 m I and at U.O m I. At this last level, w = -15.3; hence the spectrum, 

 which also looked doubtful, was discarded. 



Five of the auto-spectra of the vertical velocities are shown in figure V-23A. 

 These spectra cover a wide range of depths, from 0.5 meter down to 10.0 meters. 

 Clearly, most of the high frequency wind wave energy (above 500-600 mcps) has been 

 filtered at depths of 7 meters and beyond. The spectral peaks, as with the 

 BBELS-5 curves, show a definite "reddening" with depth - from 300 mcps (3-3 sec) 

 at 0.5 meter down to 50 mcps (20 sec) at a depth of 10 meters. 



Figure V-23B shows a family of horizontal velocity spectra at depths ranging 

 from 2.0 to 10.0 meters. Here again there is evidence of attenuation of spectral 

 energy with depth. The 2.0 m I curve displays a strong wind wave peak at 250 

 mcps (U sec), with a secondary peak at about 50 mcps. The other curves (6.0 m I, 



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