                   CTD CALIBRATION: CRUISE CIROLANA 6/1989                 
                                                                           
CTD used was S/N 41136.                                                    
                                                                           
Pressure  and  temperature   sensors   were  corrected  using  coefficients
determined  after laboratory calibrations.  Water samples collected  during
the  ascent of the CTD for salinity analysis with a  Guildline  salinometer
were used to calibrate the conductivity sensor.                            
                                                                           
                                                                           
Pressure                                                                   
The  pressure  sensor was calibrated with a dead weight tester  before  and
after the cruise, during June and August 1989.  However, the temperature of
the  sensor  was near 7.5degC for all of the August calibration and  during
the  June calibration the temperature/pressure values did not  reflect  the
conditions  encountered  during the cruise.  The calibration  was  repeated
using  appropriate  temperature/pressure coordinates during  November:  see
Fig. 1.                                                                    
                                                                           
P(COR) = P(CTD) + PA*T(COR) + PB*P(CTD) + PC                               
                                                                           
where T(COR) = corrected CTD temperature.                                  
          PA = -8.4343 E-2                                                 
          PB = 3.1313 E-3                                                  
          PC = 2.09                                                        
                                                                           
This  calibration  was in good agreement with that suggested  by  comparing
pressures  derived from unprotected thermometers and those recorded by  the
CTD.                                                                       
                                                                           
                                                                           
Temperature                                                                
Good agreement was obtained between pre- and post-cruise calibrations using
platinum  resistance  thermometers (although only PRT  2503  gave  reliable
measurements).                                                             
                                                                           
DSRTs were used on each CTD cast and suggested a correction which  differed
from  the  laboratory  calibration by 16 mK,  within the tolerance  of  the
thermometers.                                                              
                                                                           
Temperatures were corrected using the pre-cruise calibration of June 1989: 
                                                                           
    T(COR) = T(CTD) + TA* T(CTD)* T(CTD) + TB*T(CTD) + TC                  
                                                                           
        TA = -3.2311 E-5                                                   
        TB = 7.1947 E-5                                                    
        TC = 2.75 E-4                                                      
                                                                           
                                                                           
Conductivity ratio                                                         
The conductivity ratio of the water sample salinity, CR(WS), at its in situ
pressure  and  temperature  was compared with that  measured  by  the  CTD,
CR(CTD).  The  ratio  CR(WS):CR(CTD) was then fitted by  least  squares  to
satisfy the equation                                                       
                                                                           
        CR(WS)                                                             
        -----------     = CA * T(CTD) + CB * P(CTD) + CC                   
        CR(CTD)                                                            
                                                                           
Where T(CTD) and P(CTD) are the corrected CTD temperature and pressure.    
                                                                           
The variation in the ratio CR(WS): CR(CTD) is seen in Fig. 2.              
                                                                           
Solving  the  above equation and calculating an estimate  of  CTD  salinity
yielded  an  rms difference between water sample and CTD salinity of  0.003
for 95 observations.  This is within the expected tolerance of the CTD  and
no attempt was made to determine cell factors, CF, for each station.       
                                                                           
   CR(COR) = CR(CTD) * [CF * (CA * T(COR) + CB * P (POR) + CC]             
                                                                           
where   CF = 1.0                                                           
        CA = -0.29928 E-5                                                  
        CB = 6.10159 E-9                                                   
        CC = 1.00145                                                       
                                                                           
Fig.  3  shows how effective these coefficients are in correcting  the  CTD
estimates of salinity.                                                     
                                                                           
Ken Medler                                                                 
14 June 1991                                                               
