run a0509a 









M 9 a 9 e l 









o" 











E 



C 

 O o 



o 

 > 



<D 



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 ID N 







,kK/^ 



. L 





0.0 





75.0 



150.0 



M 









o" 











'e 











c 



O o 



o 

 > 



at 



0) (M 



aA 





k k 



ft. A. 





150.0 



CM 





225.0 



300.0 



1 











c 



O o 

 



> 







_> 



ID (M 



N 



A 



A A, * ,/V 



— K c= As- 











300. 





375.0 



450.0 



IM 









id- 











's 











c 



O o 

 



> 



ID 





JK 





M 





JvY 



K A, 



M'l L 





450.0 





525.0 



time (sec) 



600.0 



Figure 4-5. Sample of raw and low-pass signals from Gauge I, Run A0509A 



application of the low-pass filter with a cutoff frequency of one-half the peak 

 frequency of the incident spectrum, is again shown as the dashed curve. In 

 addition, Figure 4-5 also shows the sand bed signal as identified by the algo- 

 rithm described in the previous sections. In this case, the downward trend in 

 the signal indicates that the sand bed is eroding over time. After 9 min of 

 wave action, the sand surface eroded 3.4 cm in this case. After a second 

 9-min data sample (not shown), with some intervening downtime while data 



Chapter 4 SUPERTANK Swash Measurements 



87 



