                       CTD CALIBRATION: Cruise Meteor 49                   
                                                                           
CTD Instrumentation, Calibration and Data Processing:                      
                                                                           
Two instruments were used, the Multisonde (KROEBEL, 1973) and, as a back-up
device,  the Bathysonde (HINKELMANN,  1957).  Both units measure electrical
conductivity,  temperature and hydrostatic pressure.  They are lowered on a
single-conductor cable.  The number of profiles obtained are summarised  in
Table 1. The manufacturer's specifications are given in Table 2.           
                                                                           
In  order to check the calibration during the experiment,  a Nansen  bottle
with  two protected reversing thermometers was attached to the cable  close
to  the  underwater unit.  Various combinations of 9 thermometers  on  F.S.
`Meteor' were used.  59 water samples were taken mostly from the upper 20 m
on F.S. `Meteor' during Multisonde casts.  It was assumed that a proper re-
calibration could be achieved by determining the off-set in temperature and
conductivity  at  these  depth levels.  The pressure off-set was  found  by
reading the pressure value at the sea surface. There was no time dependence
of these re-calibration terms.                                             
                                                                           
The  results of the re-calibration analysis are summarised in Table 3.  The
salinity  measurements  of  the  Nansen samples were carried  out  using  a
Beckmann  RS7B  lab  and  an Autosal  8400  salinometer.  Conductivity  was
calculated  from the salinity values by an iterative reversal of Fofonoff's
(1974) formula using Newton's formula (Peters, 1978).                      
                                                                           
Due  to  the slow response of the Multisonde thermometers compared  to  the
conductivity  sensors,  spikes  occurred  in  the  salinity  profiles.  The
thermometer time constants were changed in the calculations to optimise the
spike  reduction.  After clipping remaining spikes in salinity,  a  running
mean over about 0.5 dbar was taken.  The data were then interpolated to 0.5
dbar increments and, again, a running mean over 1.5 dbar was calculated.  A
detailed  description  of  this kind of data editing was  given  by  Peters
(1976).                                                                    
                                                                           
                                                                           
Table 1. Summary of the profiling measurements onboard F.S. Meteor         
                                                                           
                Phase 0    Phase 1    Phase 2                              
No. of             6         1303       3316                               
Profiles                                                                   
                                                                           
No. of good                                                                
Quality            6         1250       3293                               
profiles                                                                   
                                                                           
Throughout all Phases, the lowering depth was 60 - 1600m, the lowering     
speed was 60 m/min and the sampling rate was 10/sec.                       
                                                                           
                                                                           
Table 2. Manufacturers Specifications (Multisonde)                         
                                                                           
Pressure      range              0-6000dbar                                
                                 0-600dbar                                 
              accuracy of                                                  
              calibration        +/- 0.01 %                                
                                                                           
              repeatability      +/- 0.3 %                                 
                                                                           
              resolution         0.1 dbar                                  
                                                                           
Temperature   range              -2 to + 40 degC                           
                                                                           
              accuracy of                                                  
              calibration        +/- 0.01 degC                             
                                                                           
              repeatability      +/- 0.001 degC                            
                                                                           
              resolution         +/- 0.001 degC                            
                                                                           
Conductivity  range              5 to 55 mmho/cm                           
                                                                           
              accuracy of                                                  
              calibration        +/- 10 micro mho/cm                       
                                                                           
              repeatability                                                
              within 6 months    +/- 20 micro mho/cm                       
                                                                           
                                                                           
                                                                           
Table 3. Recalibration data of CTDs                                        
                                                                           
PRESSURE OFF-SET[dbar] 600 dbar     -0.8                                   
PRESSURE OFF-SET[dbar] 6000 dbar    3.0                                    
T(NANSEN) - T(CTD) [degC]           0.012 +/- 0.005                        
Delta T(NANSEN) [degC]              0.009 +/- 0.003                        
C(NANSEN) - C(CTD) [10E-3 S/cm]     -0.0451 +/- 0.0048                     
TIME CONSTANT OF THEMOMETER [ms]    75                                     
                                                                           
where:                                                                     
                                                                           
PRESSURE OFF-SET:      CTD pressure reading at the surface                 
T(NANSEN):             Temperature reading of reversing thermometer        
T(CTD):                Temperature reading of CTD                          
T(NANSEN) - T(CTD):    Mean difference between reversing thermometer and   
                       CTD temperature reading                             
Delta T(NANSEN):       Mean temperature between two reversing thermometers 
                       In a Nansen bottle                                  
C(NANSEN):             Conductivity determined from Nansen bottle sample   
C(CTD):                Conductivity reading of CTD                         
C(NANSEN) - C(CTD):    Mean difference between Nansen bottle and CTD       
                       Conductivity reading                                
TIME CONSTANT:         The best time constant of the thermometer to        
                       optimise the reduction of salinity spikes           