SL ; Source Level, a measure of on-axis acoustic intensity of the 

 transmitted signal. 



40 Log R + 2qR : Two way transmission loss from the transducer 

 down to the scattering volume of interest and back to the 

 transducer. The 40 Log R component is due to spherical spreading 

 loss, while the 2aR loss is due to absorption (primarily a 

 function of frequency) . 



S,_, + 10 Log V : A measure of the backscattering strength due to 

 volume reverberation. It is the Sy term which will correlate 

 with concentration of scatterers, or total suspended matter. V 

 is a measure of the backscattering volume which will increase 

 with depth as the volume of water encompassed by the acoustic 

 signal increases due to the transducer beam pattern. 



RS : Receive Sensitivity or transfer function of the receiving 

 transducer in conversion of the echo pressure wave to an 

 electrical voltage. 



GAIN : Overall receiver gain, including Time Varying Gain (TVG) . 



Examination of Equation 3, when using the Datasonics 

 Model DFS-2100 Acoustic Remote Sensing System, reveals the 

 following: 



1. The receiver gain incorporates TVG which 

 compensates precisely for the 40 Log R + 2aR 

 transmission loss term. These two terms then 

 fall out of the equation. If overall gain is 

 changed, however, the change must be factored 

 into the calculations. 



2. Receive Sensitivity is a constant, determined 

 by laboratory measurement. This term can be 

 ignored in making concentration calculations 

 from acoustic observations because relative 

 concentration measurements, with respect to 

 measured total suspended matter samples, are 

 being made. 



3. Source Level may be ignored so long as it 

 remains constant. It must be accounted for 

 whenever a change is made. 



^' ^o rms' "^^^ measured receiver output, is then 

 proportional to S-y + 10 Log V. V is a 

 function of pulse width, equivalent beamwidth 

 and range (R) from the transducer to 

 scattering volume. V is a measure of the 

 reverberating volume at any given depth. 



