***  Documentation  for the CTD data collected on  RRS  Challenger  Cruise                                                          
23/87   (8 Dec 1987 - 21 Dec 1987)  by  the  School  of  Ocean   Sciences,                                                          
University College of North Wales, Menai Bridge, U.K., under the direction                                                          
of A.E. Hill  ***                                                                                                                   
                                                                                                                                    
DATA COLLECTION                                                                                                                     
The  instrument  used was a Neil Brown Instruments System  Mark  III  CTD.                                                          
Observed  parameters  were  pressure, temperature  and  conductivity.  The                                                          
instrument was lowered as slowly as possible,  at about 1 m/s.  In general                                                          
the  CTD was lowered to within 5-10 metres of the seabed,  except on  some                                                          
slope stations when a rising slope prevented this. The data were logged on                                                          
a BBC microcomputer.                                                                                                                
                                                                                                                                    
CALIBRATION                                                                                                                         
There were some rogue calibration data points.  On examination these  were                                                          
found  to have been collected in areas of strong temperature  or  salinity                                                          
gradients and have been omitted from the statistics.                                                                                
                                                                                                                                    
Temperature:                                                                                                                        
The temperature calibration readings were made using a digital thermometer                                                          
and  standard reversing thermometers.  The latter were found to give  very                                                          
different  readings  from  the digital thermometer which  gave  very  good                                                          
agreement with the CTD sensor.                                                                                                      
                                                                                                                                    
     Mean temperature difference (digital thermometer - CTD) = 0.000                                                                
     Standard Deviation                                      = 0.002                                                                
     Variance                                                = 0.000                                                                
     No. of points                                           =  78                                                                  
                                                                                                                                    
     Temperature = CTD temperature + 0.000 (degrees C)                                                                              
                                                                                                                                    
Salinity:                                                                                                                           
Water  samples  for salinity determinations were taken on most  casts;  on                                                          
some casts, particularly the deeper ones, more than one calibration sample                                                          
was taken.                                                                                                                          
                                                                                                                                    
     Mean salinity difference (Water sample - CTD)  =   0.0147                                                                      
     Standard Deviation                             =   0.0081                                                                      
     Variance                                       =   0.0000                                                                      
     No. of points                                  =   140                                                                         
                                                                                                                                    
     Salinity = CTD salinity + 0.0147 (PSU)                                                                                         
                                                                                                                                    
Pressure:                                                                                                                           
There was an offset of 1.7 decibars, i.e.                                                                                           
                                                                                                                                    
     Pressure = CTD pressure - 1.7 (decibars)                                                                                       
                                                                                                                                    
                                                                                                                                    
DATA PROCESSING                                                                                                                     
The  University's  mainframe computer was used for  processing  the  data,                                                          
using an in-house Pascal CTD package. The data were checked for  erroneous                                                          
readings and the up and downcasts were averaged.   The calibration details                                                          
were applied and the data were processed into 1m depth bins.                                                                        
                                                                                                                                    
Reference:                                                                                                                          
Mitchelson-Jacob,  E.G., Hill, A.E. and Simpson, J.H.  A report on the CTD                                                          
data  collected west of Scotland during the winter of 1987-88 as  part  of                                                          
the  Scottish  Coastal Current and Autumnal Circulation  Experiment  (ACE)                                                          
programmes.  School of Ocean Sciences, University College of North  Wales.                                                          
January 1989.                                                                                                                       
