do Memory Systems QFA-700 tape drive. The data tapes and a tape drive are 

 stored at the U.S. Army Engineer Waterways Experiment Station. 



Experiment Apparatus 



Instrument description 



RD Flow operated two acoustic systems during the first 2 weeks of 

 SUPERTANK. One system was a prototype of an off-the-shelf instrument 

 designed primarily for water velocity measurements. The second was an 

 experimental system built from modules procured individually. The two 

 systems were not equivalent; the return echo, for example, was processed 

 quite differently. 



Instrument 1. A 2.4-MHz prototype BB-ADCP measured the acoustic 

 backscatter and the radial velocity component along multiple acoustic beams. 

 In SUPERTANK, the BB-ADCP had three operating beams: one vertical 

 beam and two beams slanted 30 deg (0.52 rad) from the vertical. One of the 

 slanted beams pointed onshore and one pointed offshore (Figure 8-1). The 

 radial velocity components measured along each beam were used to form 

 spatially averaged estimates of the along-channel velocity component u and the 

 vertical velocity component w. The measurements were made at a series of 

 vertical levels spaced 8 cm apart. 



2 . 5 meters 



offshore Onshore 

 Vertical 



1.2 meters 



Bin Size - 8 cm 



Figure 8-1 . Orientation of the three-beam BB-ADCP 



As the name indicates, the BB-ADCP is distinguished from other ADCPs 

 by having a higher acoustic and processing bandwidth. Roughly speaking, 

 this improvement translates into a better vertical resolution. 



Chapter 8 ADCP Measurements at SUPERTANK 



139 



