*** Documentation for CTD Data collected by B.I.O.  Hesperides,  8/93 (4-26                                                         
August 1993) by the University of Wales Bangor,  UK under the Direction  of                                                         
E.D. Barton***                                                                                                                      
                                                                                                                                    
The  instrument  was  a new Sea-Bird  Electronics  SBE-911  which  measured                                                         
conductivity,   temperature,  pressure,  fluorescence,  transmittance   and                                                         
dissolved oxygen.                                                                                                                   
                                                                                                                                    
In order to calibrate the different sensors in the CTD system water samples                                                         
and temperature readings were routinely taken during most of the CTD casts.                                                         
Salinity samples were drawn from the Niskin Bottles on the General  Oceanic                                                         
Rosette  sampler and analysed on board in a Guildline Autosal  salinometer.                                                         
Temperature  readings   were   taken   from   recently  calibrated  digital                                                         
thermometers.                                                                                                                       
                                                                                                                                    
There were 43 temperature comparisons and 70 salinity comparisons. The mean                                                         
temperature  difference  was 0.01 degrees C with a  standard  deviation  of                                                         
0.012  degrees C.  While the mean salinity difference was 0.0005 psu with a                                                         
standard deviation of 0.0041 psu.  In both cases the mean was so small that                                                         
it  was  not  considered   necessary   to   make  any  corrections  to  the                                                         
manufacturer's CTD calibration.                                                                                                     
                                                                                                                                    
In the case of the Seatech transmissometer, the calibration procedure calls                                                         
for  the measurement of the output voltage with the light path (a)  blocked                                                         
and  (b)  in the air.  Blocked measurements were satisfactory giving  0.000                                                         
volts (manufacturer's value 0.005 volts).  Air readings were variable  even                                                         
after  careful cleaning of the window of the instrument;  the 'best'  value                                                         
would  have implied multiplication of transmissometer volts by  4.806/4.61,                                                         
so that observed maximum values in the sea of 4.50 volts became 4.69 volts,                                                         
corresponding   to  a  transmission  of  93.8%,  in  excess  of  the  91.3%                                                         
transmission   of   pure  water.  It  was  thus  decided  to   accept   the                                                         
manufacturer's calibration (carried out in November 1990).                                                                          
                                                                                                                                    
The Oxygen values use the manufacturers calibration values for April 1993.                                                          

