                   CTD CALIBRATION: CRUISE CIROLANA 6/1986                 
                                                                           
CTD profiles were corrected using calibration coefficients derived from the
second  half  (6B) of the cruise,  as all the water  sample  salinity  data
collected  during  the  first  part of the  cruise  (6A)  were  unreliable.
Attempts  were  made  to  use the CTD calibration  coefficients  of  6B  to
calibrate the CTD data in cruise 6A.  A summary of the results is presented
herein.                                                                    
                                                                           
                                                                           
Temperature                                                                
CTD temperature was corrected by applying the coefficients derived from the
laboratory calibration of the March 1986 data:                             
                                                                           
    T(cor) = T(ctd) + dT                                                   
                                                                           
where   dT = c + b*T(ctd) + a*T(ctd)*T(ctd)                                
And      a =  0.5610717x10-4                                               
         b =  0.505757x10-2                                                
         c = -0.557716x10-1                                                
                                                                           
                                                                           
Pressure                                                                   
CTD  pressure was corrected by applying the coefficients derived  from  the
laboratory calibration of April 1986:                                      
                                                                           
    P(cor) = P(ctd) + dP                                                   
                                                                           
where   dP = a*T(cor) + b*P(cor) + c                                       
and      a =  0.46693426                                                   
         b =  0.0025209785                                                 
         c = -8.2307014                                                    
                                                                           
                                                                           
Conductivity Ratio                                                         
CTD  conductivity was corrected by converting water sample salinity  to  in
situ  conductivity  (from  the UNESCO algorithm) and comparing  it  to  CTD
conductivity  values.  The  water sample salinity  was  measured  using  an
AutoLab bench salinometer.  A least squares regression was performed on the
corrected data to derive the calibration coefficients a, b and c:          
                                                                           
   CR(ws)/CR(ctd) = a*T(cor) + b*P(cor) + c                                
                                                                           
The corrected conductivity ratio is then calculated from:                  
                                                                           
   CR(cor) = CR(ctd)*(a*T(cor) + b*P(cor) + c))                            
                                                                           
and      a =  0.21589015x10-4                                              
         b = -0.525843206x10-7                                             
         c =  0.99895747                                                   
                                                                           
The derived P,  T and CR calibration coefficients were used to correct  the
CTD  profiles  of  cruise  6/86.  The results were compared  with  the  0-S
regression suggested by Peter Saunders.                                    
                                                                           
                                                                           
Results                                                                    
Station details are shown in Table 1. The root mean square (rms) difference
between the corrected CTD salinity and water sample salinity from cruise 6B
was 0.003 for 55 data values.  This was found to be acceptable,  in view of
the errors inherent in the CTD and bench salinometer.                      
                                                                           
The  validity  of the calibrated salinity of the stations was  measured  by
comparing  the  0-S relationship with that suggested by P.  Saunders  (S  =
34.698 + 0.0900).                                                          
                                                                           
The  rms  difference between the corrected CTD salinity  and  P.  Saunders'
calculated  salinity for each station are given in Table 2.  In 6A the  0-S
relationship deviated from the P.  Saunders' line.  The rms difference  got
better  by  the  end of cruise 6A but the rms difference of  the  last  two
stations was still 0.010 and 0.009 respectively.                           
                                                                           
The CTD data from the second half of the cruise were in good agreement with
the P. Saunders' line and the rms difference was generally <0.007.         
                                                                           
                                                                           
Conclusion                                                                 
Calibration  constants  for  correcting CTD data from the  second  half  of
cruise  Cirolana  6/86  have been derived.  The corrected CTD  salinity  of
cruise  6B  is  generally in good agreement with P.  Saunders'  linear  0-S
relationship, i.e.  rms is generally <0.007,  which is within the tolerance
of the system accuracy.  However, the deviations of cruise 6A data are much
greater (i.e. 0.009 to 0.022) and are unacceptable.  Hence, no CTD profiles
of cruise 6A were corrected.                                               
                                                                           
                                                                           
Jackie Cooper                                                              
17th May 1990                                                              
                                                                           
                                                                           
Table 1: Station details for cruise 6/1986                                 
Station      Latitude       Longitude       Date                           
09          46 01.00 N     11 00.20 W     20 June                          
10          44.49.17 N     14 09.63 W     21 June                          
12          42 54.44 N     14 07.79 W     21 June                          
15          42 54.39 N     14 09.13 W     21 June                          
17          42 55.14 N     14 11.26 W     22 June                          
19          42 54.95 N     14 09.92 W     22 June                          
21          42 54.02 N     14 10.05 W     22 June                          
24          43 09.91 N     16 44.25 W     23 June                          
27          44 24.75 N     19 15.00 W     23 June                          
31          45 54.70 N     20 25.01 W     24 June                          
34          47 20.04 N     20 10.15 W     24 June                          
36          47 21.35 N     20 08.83 W     25 June                          
41          45 50.17 N     17 35.14 W     25 June                          
42          45 59.98 N     17 20.10 W     26 June                          
45          45 59.83 N     16 45.05 W     26 June                          
48          47 19.73 N     16 49.26 W     28 June                          
50          46 55.33 N     14 44.44 W     05 July                          
51          48 14.66 N     14 24.16 W     05 July                          
52          49 32.82 N     16 39.67 W     06 July                          
53          49 32.70 N     16 39.92 W     06 July *                        
55          49 15.15 N     18 44.49 W     07 July *                        
56          50 59.45 N     18 51.17 W     07 July                          
72          52 11.77 N     17 53.33 W     10 July                          
83          51 02.60 N     15 20.02 W     12 July                          
86          51 00.15 N     15 20.07 W     13 July                          
87          51 03.34 N     15 14.05 W     13 July                          
88          51 04.04 N     15 10.39 W     13 July                          
89          51 04.91 N     15 03.60 W     13 July                          
                                                                           
* Poor quality, not to BODC                                                
                                                                           
                                                                           
Table 2: The rms difference between corrected CTD salinity and P. Saunders'
straight line.                                                             
Cruise     Station     RMS     Observations                                
6A         09          0.022   398                                         
6A         19          0.012   326                                         
6A         42          0.012   416                                         
6A         45          0.010   337                                         
6A         48          0.009   362                                         
6B         50          0.007   447                                         
6B         51          0.006   421                                         
6B         52          0.009   342                                         
6B         53          0.006   380                                         
6B         55          0.006   328                                         
6B         56          0.007   450                                         
6B         72          0.006   325                                         
6B         83          0.007   131                                         
6B         86          0.007   160                                         
6B         87          0.006   106                                         
6B         88          0.009    36                                         
