Comparison of LDV and OFS concentration estimates 



The sediment concentration derived from LDV measurements is compared 

 with the OFS results in Figure 11-10. As described earlier, the lowest OFS 

 elevation is slightly above the highest LDV measurement station. Both instru- 

 ments were carried on the traverse mechanism to provide simultaneous verti- 

 cal profiles of the flow and sediment distribution. The OFS registers the 

 optical scattering intensity from all suspended material. In order to extract the 

 component that is contributed by the bottom sand, it was assumed that the 

 uppermost measurement of the OFS (z = 32.6 cm) is derived from fine parti- 

 cles; this was treated as background noise and subtracted from the measured 

 signals. The OFS and LDV data were then "matched" at the quasi-overlap 

 region to produce the curve in Figure 1 1-10. The smooth continuation of the 

 two measured profiles supports the contention that the data rate of the LDV is 

 directly related to the sediment concentration. 





10 2 

















1 1 1 1 





















X 



X 









- 













X X 











u 



N 



10 1 



\ 













- 





/ 



10° 

 10 













 



o 



- 





-2 



10 1 





10° 





10 



1 









n 









Figure 11-10. Sediment concentration profile produced from a composite of LDV (o) and 

 OFS (x) data. Run S0315A 



230 



Chapter 1 1 LDV in the Bottom Boundary Layer 



