*** Documentation for STD data collected on RRS Discovery Cruise 48 (Jul -                                                          
Aug  1972)  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,  with a Rosette water sampler                                                          
attached to the wire above it.  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.).  The only exception to this scheme was at station 8050 where                                                          
the digitisation was at 5m intervals.                                                                                               
                                                                                                                                    
The STD data was collected on a grid of 25 stations,  covering an area  of                                                          
25 x 25 miles with stations 5 miles apart.  At each station the STD  probe                                                          
and  the Rosette sampler were lowered to 500m,  or to about 5m  above  the                                                          
bottom where the depth was shallower.  Stations were identified by their 4                                                          
digit Discovery station number.  Time series measurements were taken at  2                                                          
stations.  The first was at station 8050 and consisted of STD dips to 450m                                                          
every  hour and  water sampling with Rosette sampler every  4  hours.  The                                                          
programme continued for 4 days.   The second time series was  obtained  at                                                          
station 8051,  where STD dips were made every half hour  to  approximately                                                          
100m, and  Rosette bottle samples were taken every 3 hours over  a  2  day                                                          
period.  For stations 8050 and 8051 individual dips are identified by  the                                                          
4 digit Discovery station number,  followed by the sequence number  of the                                                          
dip (from 01 to 98).                                                                                                                
                                                                                                                                    
The absolute accuracies of the temperature and salinity measurements  were                                                          
checked by comparison with a series of 87 temperature measurements and 133                                                          
salinity  samples obtained with reversing thermometers and  water  bottles                                                          
over the course of the cruise.   From this comparison,  made at depths  of                                                          
25m, 300m and 600m, a small calibration constant was derived for salinity.                                                          
No  correction  was  necessary for the temperature  sensor.   The  maximum                                                          
precision  error  in  salinity was estimated to  be  generally  less  than                                                          
+/- 0.04 ppt, but as much as +/- 0.07 ppt in regions of strong temperature                                                          
gradient where spiking was more pronounced.   The maximum precision  error                                                          
in  temperature  was  estimated to be  less  than  +/- 0.05 degC.   Errors                                                          
introduced  by  digitisation  were  negligible,   the  resolutions   being                                                          
+/- 0.01 ppt  in the salinity scale and +/- 0.01 degC in  the  temperature                                                          
scale.                                                                                                                              
                                                                                                                                    
References:                                                                                                                         
RRS  Discovery Cruise 48,  July - August 1972 Upwelling off the  coast  of                                                          
north-west Africa.   National Institute of Oceanography Cruise Report  No.                                                          
53. January 1973.                                                                                                                   
                                                                                                                                    
Johnson,  D.R.,  Barton,  E.D.,  Hughes,  P.  and  Mooers,  C.N.K.    1975                                                          
Circulation  in  the Canary Current upwelling region off Cabo  Bojador  in                                                          
August 1972.  Deep Sea Research  Vol. 22 p 547 - 558                                                                                
