Documentation  for  the SeaSoar data collected on Bon  Entente  10/09/86  -                                                         
06/10/86  off  the  Coast  of Portugal by the  School  of  Ocean  Sciences,                                                         
University of Wales, Bangor, under the direction of E.D. Barton.                                                                    
                                                                                                                                    
The  SeaSoar is an instrument which enables a standard Neil Brown Mark  III                                                         
CTD to be towed beneath the sea surface at controllable depths. The vehicle                                                         
used  was capable of carrying a large suite of sensors,  at speeds up to 10                                                         
knots  (5  m s-1) and to a maximum depth of 400 m  in  optimal  conditions,                                                         
following  a  controlled and adjustable path.  The SeaSoar comprises of  an                                                         
underwater  vehicle,  into which is mounted a Neil Brown Mark III  CTD  and                                                         
Chelsea  Instruments fluorometer,  and a deck unit which controls the pitch                                                         
of the SeaSoar wings enabling the vehicle to climb or dive as required.                                                             
                                                                                                                                    
The  streamlined SeaSoar vehicle was towed using a faired cable at a  speed                                                         
of about 4 m s-1.  This enabled the instrument to cycle between 0 and 325 m                                                         
depth,  approximately  every  10  -  12  minutes,  which  gives  a  spatial                                                         
horizontal  resolution of about 2 km.  The Neil Brown Mark III CTD  sampled                                                         
every second for pressure, temperature, conductivity and chlorophyll.                                                               
                                                                                                                                    
Because  of the continuous and undulating path of the  SeaSoar  instrument,                                                         
the  CTD  instrument salinity calibration was done by taking  water  bottle                                                         
samples  from  the  continously pumped onboard  source.  Samples  from  the                                                         
surface  pump  were  taken just prior to the SeaSoar reaching  the  surface                                                         
because the SeaSoar was trailing the ship by some 600 m. In this way it was                                                         
intended that the water masses sampled by the water bottle and the  SeaSoar                                                         
should  be similar.  The salinity samples were drawn from the water bottles                                                         
and analysed on a Guildline 8400A Autosal salinometer.  The in situ  sample                                                         
bottle  salinities  were compared with the CTD salinities when the  SeaSoar                                                         
was  near-surface.  A few of the in situ calibration differences were  much                                                         
larger  than the others,  as much as several standard deviations,  and were                                                         
eliminated from the data set.  These usually occurred in regions of  strong                                                         
horizontal  or  vertical gradients where spatial errors are most likely  to                                                         
occur. A linear calibration equation was determined by least-squares linear                                                         
regression  between  the in situ water bottle salinities  and  the  surface                                                         
SeaSoar readings.                                                                                                                   
                                                                                                                                    
The  SeaSoar  CTD   surface   temperatures   were  calibrated  against  the                                                         
Thermosalinograph  (THS)  temperatures  which had been  calibrated  in  the                                                         
laboratory.  A linear calibration equation was determined by comparing  the                                                         
THS  temperatures  and the SeaSoar surface temperatures by a  least-squares                                                         
linear regression technique. The CTD pressure sensor had been calibrated in                                                         
the laboratory prior to the cruise. A chlorophyll sensor was also fitted to                                                         
the CTD and this was calibrated against the water bottle samples.                                                                   
                                                                                                                                    
The  data were gridded by the SURFACE-II (Sampson 1975) system  into  files                                                         
with a horizontal time separation of 12 minutes (navigation data were added                                                         
later) and a vertical spacing of 5 m using an octant gridding procedure. By                                                         
using  the  octant  search procedure specified the  data  were  effectively                                                         
filtered,  each  grid  node  having  been  smoothed  over  a  distance   of                                                         
approximately  5  km  in  the  horizontal and 20 m  in  the  vertical.  The                                                         
available  navigation  data were merged with the SeaSoar data,  which  were                                                         
then  organised into files representing cruise grid lines.  The data  files                                                         
were  then  examined  and any remaining spikes in  the  data  were  removed                                                         
interactively,  the  data  points  that were  rejected  being  replaced  by                                                         
linearly interpolated values.                                                                                                       
