a. Mean horizontal velocity profile over the averaging period. 



b. Largest magnitude of u and w velocity over the measurement interval. 



c. Profile of standard deviation of u and w components. This profile is a 

 measure of the wave energy as a function of depth. 



d. Power spectra of u and w shown at middepth. The spectra are aver- 

 aged over three adjacent bins located midway between the transducers 

 and the bottom. 



Backscatter data. Range normalized backscatter data are presented in 

 units of decibels relative to the background noise level. Before computing 

 statistics, data were range normalized as described in Experiment Procedures. 

 After applying the corrections for water absorption and for geometrical 

 spreading, the resulting profiles still seemed to contain a loss term that was 

 linear with range. The most likely explanation for this loss is scattering 

 and/or viscous particle attenuation. A fixed value of particle attenuation of 

 1.3 db/m (one-way) removed most of this trend and subsequently was applied 

 to all the data presented in Appendix H (contained in Volume n of this 

 report). For each run, three backscatter plots were generated for the same 

 time intervals as the velocity plots: 



a. Profile of minimum (dashed), mean (solid), and maximum (dash-dot) 

 range normalized scatter strength. 



b. Standard deviation of the scattering strength over the 5-min measure- 

 ment interval. These numbers represent the sum of natural variations 

 in the amount of suspended material and a fixed contribution from 

 purely statistical effects. 



c. Power spectra of the scattering strength recorded 5 cm (solid), 10 cm 

 (dashed), and 30 cm (dash-dot) above the bottom. 



Data file format 



Both 600-kHz data and 2.4-MHz data were recorded in a binary file format 

 with a rather large and complex format. Source code and executable 

 programs for decoding and conversion to ASCII are available along with the 

 data tapes from the U.S. Army Engineer Waterways Experiment Station, from 

 RD Instruments of San Diego, CA, or from SonTek, Inc., San Diego, CA. 



Identification of marginal data sets 



Instrument 1. To make the short-range mode work for the 2.4-MHz 

 BB-ADCP, all hardware and software modules must work well to achieve 

 good quality data. Unfortunately, this was not the case. The 2.4-MHz BB- 



Chapter 8 ADCP Measurements at SUPERTANK 



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