194 



In V(z) = G z + O (10-4) 



where G = -^(k^l^Q and O = ±]n(AQ . The coefficients k t and Jt, 



are found by linear regression of G and C. If CfzJ, the concentration at z—z 

 in the near field, is known, then we need to know only jfcj and k^ to invert the 

 voltage-to-sediment concentration. 



Equation 10-3 can be discretized 



/=/ 

 A C, = V} exp£ {[* x + I *, (C w + Q] (z, - z^)} (10-5) 



If we divide Equation 10-5 by the following 



A C,-! = V^ exp £ {[*, + { *, (C,_, + Q] (z, - z^)} (10-6) 



we obtain the implicit expression for C„ 

 V 2 



c i = c /-i —4 exp {[*i + \ ^ (C '-i + C ^l (z * - z /-i } } ( 10 - ? ) 



w-i 



The concentration C, at z = z 7 is calculated by iteration with C hl , V M , V h k lt 

 and k 2 given. V w and V, are raw data. 



Simultaneous calibration of the ACP and the OBS in the recirculating 

 calibration cylinder assured agreement in the sediment concentrations. Use of 

 the sediment from the experiment minimized errors due to variable sediment 

 characteristics. 



The linear calibration formula is as follows: 



Y = G X + Off ( 10 " 8 ) 



where G is the calibration gain constant, Q^is the calibration offset constant, 

 and X is the uncalibrated data value. This formula was applied to data from 

 the pressure sensor, both OBS, the EMCM, and the pore pressure sensor with 

 the gain and offset values shown in Table 10-2. After applying the calibration 

 formula to the data, the resulting values for the OBS were adjusted by 

 subtracting the background concentration. The background concentration was 

 determined by averaging the OBS sensors return values during periods in 

 which waves were not being generated. In this way, the sand suspension 



Chapter 10 Intermittent Near-Bed Sediment Suspension 



