                      CTD CALIBRATION: CORYSTES 3A/1992                    
                                                                           
                                                                           
CTD: S/N 45056                                                             
                                                                           
(1)  A  total  of  88 valid profiles were  collected  during  this  cruise.
Reversing  thermometers  were  fitted to the Niskin bottles being  used  to
collect samples.  A total of 126 pairs of thermometer readings were  taken,
together with 166 pairs of salinity samples.                               
Not all the calibration data collected were used to calibrate the          
CTD:                                                                       
   (i)  Thermometer differences > 0.02 were discounted.                    
   (ii) It was apparent from inspection of differences between mean        
salinity  samples  and salinity values from the CTD that  there  were  some
large discrepancies. Consequently, only salinity values from bottom samples
excluding  those  from stations 55-67 (Humber anchor station) were used  to
derive calibration coefficients for the CTD.                               
                                                                           
                                                                           
(2)  The pressure sensor was corrected using the laboratory calibration  of
March 1992 at T = 6 deg C.                                                 
                                                                           
P(cor) = P(ctd) - 1.6                                                      
                                                                           
                                                                           
(3)  The temperature sensor was corrected using the laboratory  calibration
of March 1992.                                                             
                                                                           
T(cor) = T(ctd) + 0.011                                                    
                                                                           
It is assumed that the thermometer temperatures are accurate to 0.02 deg  C
and  the  CTD  to 0.01 deg C,  so that differences within 0.03  deg  C  are
acceptable.  Fig.  1 shows the comparison between reversing thermometer and
uncorrected  CTD  temperatures.  Out of 126 sets of  values  only  11  were
outside the acceptable range.  The mean differences of those used was 0.009
deg C.                                                                     
                                                                           
                                                                           
(4) The salinity sensor was calibrated using the equation:                 
                                                                           
    CR(cor) = CR(ctd)x[a x T(cor) + b x P(cor) + c]                        
                                                                           
where     a = -0.807779e-4                                                 
          b = -0.274751e-5                                                 
          c =  0.100025e+1                                                 
                                                                           
The rms difference between salinometer and CTD salinity was 0.008.         
                                                                           
Fig.  2 shows the distribution of differences between salinity samples  and
CTD salinity values before and after the application of the calibration.   
                                                                           
Fig.  3  shows  the ratio between the CTD conductivity  and  water  samples
conductivity  before  applying the correction.  Note the poor  quality  for
Stations 55 to 67, from the Humber Estuary.                                
                                                                           
Fig.  4  shows the differences between the water sample  salinity  and  the
uncorrected CTD value, after removal of unsuitable calibration data.       
                                                                           
Fig. 5 shows similar, but after calibration of the CTD sensors.            
                                                                           
                                                                           
(5) The general distribution of the stations on this cruise was:           
                                                                           
1-46, 140, 142      North Sea                                              
                                                                           
55-67               Humber (Killingholme) Anchor                           
                                                                           
72-83, 107-112      Humber to Wash offshore                                
                                                                           
85-101, 113-126     The Wash                                               
