*** Documentation for STD data collected on RRS Discovery Cruise 26 (Apr -                                                          
May  1969)  by the Department of Oceanography,  University  of  Liverpool,                                                          
Liverpool, U.K., under the direction of P. Hughes ***                                                                               
                                                                                                                                    
The  instrument  used  was  the University  of  Liverpool  Bissett  Berman                                                          
Salinity-Temperature-Depth  system type 9006.   The data output from  each                                                          
STD  lowering and raising was automatically recorded in analogue  form  as                                                          
plots  of  salinity and temperature against depth.   In the  near  surface                                                          
layers spiking due to the differing response times of the temperature  and                                                          
conductivity  sensors  created  a problem  in  interpreting  the  salinity                                                          
profiles.   The salinity profiles recorded by the STD system  were subject                                                          
to  spiking errors towards low salinity during lowering and  towards  high                                                          
salinity  during  raising.   A  satisfactory  method  of  eliminating  the                                                          
salinity errors was obtained by superimposing the analogue traces recorded                                                          
during  the  lowering  and  the raising of  the  STD  probe  and  manually                                                          
bisecting  the  resulting  envelopes of  salinity  and  temperature.   The                                                          
derived  profiles were then digitized at depth intervals of 3m down  to  a                                                          
depth of 300m.  Below 300m digitisation was on the basis of 2 values every                                                          
15m (i.e.  307m, 315m, 322m, 330m, 337m, etc.).  Exceptions to this scheme                                                          
are given below:                                                                                                                    
                                                                                                                                    
  RRS Discovery                                                                                                                     
   Station No.                 Digitisation scheme                                                                                  
                                                                                                                                    
      6896                     every 3m to 600m, every 15m thereafter                                                               
      6898                     2m, 5m, 7m, 10m, 12m, 15m, etc.                                                                      
      6905                     every 15m to 600m, every 30m thereafter                                                              
      6908 - 6912, 6962 - 6966 every 1m                                                                                             
      6917, 6983, 6984, 6997   every 3m to 300m, every 15m thereafter                                                               
      6930, 6947, 6958         every 6m to 600m, every 30m thereafter                                                               
      6967                     every  1m to 100m,  every 3m from  100m  to                                                          
                               300m, then 307m, 315m, 322m 330m 337m, etc.                                                          
      6969, 6971, 6982, 6998   every  3m to 300m, then 307m,  315m,  322m,                                                          
                               330m,  337m,  etc.  until 750m,  every  15m                                                          
                               thereafter                                                                                           
      6981                     7m, 15m, 22m, 30m, 37m, etc.                                                                         
                                                                                                                                    
The STD casts were usually to a depth of 500m - 750m,  but stations  6905,                                                          
6917,  6930 and 6947 went to a depth of 1500m - 2000m.   A Dahn  buoy  was                                                          
laid at station 6970,  in 746m of water,  and the STD was lowered to  300m                                                          
every  30 minutes over a period of 2 days whilst the ship  maintained  its                                                          
position.  Only the first downcast is included in this dataset.  A similar                                                          
exercise was carried out at station 6985,  with lowerings to within 5m  of                                                          
the  sea  bed,  but  these data have  not  been  included.   The  absolute                                                          
accuracies  of the temperature and salinity measurements were  checked  by                                                          
comparison with a series of temperature measurements and salinity  samples                                                          
obtained with reversing thermometers and Niskin bottles over the course of                                                          
the cruise.                                                                                                                         
                                                                                                                                    
Reference:                                                                                                                          
RRS Discovery Cruise 26, 3 April - 9 May 1969  Physical and chemical study                                                          
of  the  upwelling  area off north-west  Africa.   National  Institute  of                                                          
Oceanography Cruise Report No. 26. 6pp.                                                                                             
