2. Measure ambient and in-plume concentrations 

 of total suspended matter by analyzing water 

 samples taken in selected locations where 

 acoustic intensity could also be observed. 



3. Using the measured values of total suspended 

 matter as "ground truth", make estimates of 

 total suspended matter concentration based on 

 acoustic backscatter measurement alone. 



3.2 Methods and Analysis 



The Datasonics Model DFS-2100 Acoustic Remote Sensing 

 System was used at 200 kHz for performing the acoustic plume 

 tracking. High power output, low receiver noise levels and 

 calibrated control of signal level allows monitoring of extremely 

 low concentrations of material in the water column and 

 acquisition of suspended sediment concentration levels when 

 correlated with ground truth sampling. 



In attempting to relate acoustic backscatter 

 measurements in a plume of suspended particulate matter to 

 quantitative concentration levels, one must measure the 

 reflection, or backscattering characteristics of the material in 

 the scattering volume of interest. 



The echo or reverberation level received back at the 

 towed vehicle transducer from particulate scatterers in the 

 dredged material plume may be expressed as part of a standard 

 sonar equation as follows: (See definition of terms below) . 



RL = SL - 40 Log R - 2aR +8^+10 Log V (1) 



Equation 1 summarizes signal losses within the water 

 column. The acoustic receiver voltage output measured and 

 recorded during a survey can be defined as follows: 



out rms = RL + RS + GAIN 

 or 



RL = out rms - RS - GAIN (2) 



Equating equations 1 and 2 . 



out rms = SL-(40 Log R + 2aR) + (S^ + 10 Log V) + RS + GAIN (3) 



Definition of Terms 



RL : Reverberation Level, or backscattered acoustic intensity 

 from a random, homogeneous distribution of scatterers throughout 

 a defined volume of water. 



