***  Documentation  for CTD data collected on RRS Shackleton  Cruise  7/75                                                          
(Jul  -  Aug  1975)  by the Institute  of  Oceanographic  Sciences  Deacon                                                          
Laboratory, Godalming, Surrey, U.K., under the direction of J. Swallow ***                                                          
                                                                                                                                    
The instrument used was a Neil Brown Instrument Systems CTD which measured                                                          
pressure,  temperature and conductivity.   Up to 12 water bottles were put                                                          
on  the wire during the CTD lowering,  to provide calibration  values  and                                                          
some back-up station data.   The output was recorded on magnetic tape  and                                                          
values logged by hand at 100db intervals.  Lowering and retrieval rates of                                                          
0.5  to  1.5m/s were employed and the sensors were flushed with  distilled                                                          
water on recovery.  The sea water samples were analysed using a  Guildline                                                          
Autolab   Salinometer.   Reversing thermometers were   calibrated   before                                                          
and after the cruise.                                                                                                               
                                                                                                                                    
PRESSURE: In-situ  calibration was possible by comparison between the  CTD                                                          
and   the  pressure  determined  from  pairs  of  reversing   thermometers                                                          
(protected and unprotected).                                                                                                        
                                                                                                                                    
TEMPERATURE: In-situ  calibration  was possible by comparing  of  the  CTD                                                          
temperatures  and reversing thermometers separating the deep  and  shallow                                                          
measurements.                                                                                                                       
                                                                                                                                    
SALINITY:  The salinity data were calibrated using one set of  calibration                                                          
constants for the entire leg of the cruise.  These were determined from 10                                                          
water samples on each station.                                                                                                      
                                                                                                                                    
Original  values  were  averaged  over  an  interval  of  one  second  and                                                          
calibration coefficients and correction factors applied.   A time constant                                                          
correction  algorithm was employed to compensate for  the slower  response                                                          
of  the platinum resistance thermometer.  Differences  between  successive                                                          
values  of  each  parameter were examined;  the mean  difference  and  its                                                          
standard  deviation  calculated and values greater than  several  standard                                                          
deviations from the mean difference were checked.  Genuinely suspect  data                                                          
were  then  replaced  by  interpolated  values.  Derived  quantities  were                                                          
computed  from  algorithms published by Fofonoff et al (1974).   The  data                                                          
have been averaged to give 1 value approximately every decibar.                                                                     
                                                                                                                                    
References:                                                                                                                         
RRS Shackleton Cruise 7/75,  21 July - 14 August 1975 Current Measurements                                                          
and Hydrographic Stations between Seychelles,  Madagascar and East Africa.                                                          
Institute of Oceanographic Sciences Cruise Report No. 37. 1975.                                                                     
                                                                                                                                    
Fofonoff,  N.P.,  Hayes,  S.P. and Millard Jr.,  R.C.  1974 WHOI/Brown CTD                                                          
microprofiler:  methods  of  calibration and  data  handling.  Woods  Hole                                                          
Oceanographic Institution  WHOI-74-89.                                                                                              
