


     GP5-95-DI
     NOAA Ship Discoverer
     San Francisco, California - Manzanillo, Mexico
     August 2 - 24, 1995

     Chief Scientist: Mr. Ben Moore
     Survey Department: CST P. Harper, J. Davis, N. Shoji
     CTD Personnel: Ship's Survey Department
     Final Processing: K. McTaggart, M. O'Haleck


     ACQUISITION: 

     Twenty-seven CTD profiles were collected during this cruise covering 
     two meridionals from 8N to 8S.  Seventeen profiles were collected along 
     110W, and 10 along 95W.  The majority of casts were to 1000 m; 10 casts 
     were deep.  A test cast was made during the transit from Seattle to 
     San Francisco.  These data were not processed.

     All casts used TAO's Sea-Bird 9plus CTD s/n 09P10881-0390 measuring 
     pressure (s/n 58950), temperature (s/n 1708), and conductivity (s/n 1467).
     The CTD was mounted in a custom 24-bottle frame with a Sea-Bird rosette 
     sampler.  The CTD data stream was passed through a Sea-Bird 11plus deck 
     unit (s/n 376) with factory settings.  An analog signal was recorded onto
     the audio portion of VCR tape as a backup.  Digitized data were sent to a Zenith personal 
     computer equipped with Sea-Bird's SEASOFT acquisition software (version
     4.207) where calibrated data were displayed in graphical form in real-
     time, as well as stored in raw form onto the hard disk.  Backups of 
     the raw data were made on 40 Mbyte 1/4" cartridge tapes and returned 
     to PMEL for post-cruise processing.

     Station 4 data are from a VCR tape replay at sea.
   

     SALINITIES:

     Salinity analysis was performed using Guildline Autosal salinometers
     s/n 56.118 or 56.119 (last calibrated at NRCC June, 1995).  IAPSO standard 
     seawater batch #P105 was used for casts 1-13; batch #P122 was used for
     casts 14-27.  NRCC calibrations were not applied to the bottle salinities
     used to calibrate this data set, only a drift-during-run linear 
     interpolation correction.  Standard operating temperature was 24 degrees 
     Celsius.


     POST-CRUISE CONDUCTIVITY CALIBRATIONS:

     GP595A.CAL was created at PMEL using program SBECAL.  Anomalous 
     differences between CTD and bottle salinities were scrutinized.
     Bottle salinities were checked against their original log sheets 
     for typos.  Several autosal runs jumped in conductivity by approximately
     0.03 mS/cm possibly owing to changing trim adjustment.  Deep CTD traces 
     overlayed well at these jumps.  P18 data also confirmed which autosal
     runs were bad.  As a result, casts 11-17 and 23-26 bottle data were not
     used in the fitting routines for conductivity.

     Final pressure and temperature calibrations were pre-cruise.  
     Conductivity calibration coefficients were best determined using a 
     station-dependent linear fitting routine, CALCOS1, written by 
     Greg Johnson in MATLAB.  Over 91% of 160 points were used in the fit
     with a standard deviation of 0.00349.  The bias computed was 
     -0.00089720257 mS/cm, and the slope ranged from 1.0008018 at station 1 to
     1.000415 at station 27.  Slope and bias values were applied to CTD
     data using PMEL Fortran program GP595_EPIC; and to bottle files using
     CALMSTR5.


     FINAL PROCESSING:

     The following are the standard SEASOFT processing modules used to
     reduce Sea-Bird CTD data:

     DATCNV converts raw data to engineering units and creates a bottle
     file if a Sea-Bird rosette sampler was used.  (MARKSCAN creates a 
     bottle file if a General Oceanics rosette was used.)

     ROSSUM averages the bottle data specified in the DATCNV or MARKSCAN
     output and derives salinity, theta, sigma-t, and sigma-th.  These
     bottle files are transfered to the PMEL VAX where post-cruise 
     calibrations are computed.

     WILDEDIT makes two passes through the data in 100 scan bins.  The
     first pass flags points greater than 2 standard deviations; the
     seond pass removes points greater than 20 standard deviations from
     the mean with the flagged points excluded.

     CELLTM uses a recursive filter to remove conductivity cell thermal
     mass effects from the measured conductivity.  In areas with steep
     temperature gradients the thermal mass correction is on the order
     of 0.005 psu.  In other areas the correction is negligible.  The
     value used for the thermal anomaly amplitude (alpha) is 0.03.  The
     value used for the thermal anomaly time constant (1/beta) is 9.0.
 
     FILTER applies a low pass filter to pressure with a time constant of
     0.15 seconds, and to conductivity with a time constant of 0.03 seconds.
     In order to produce zero phase (no time shift) the filter is first
     run forward through the file and then run backwards through the file.

     LOOPEDIT removes scans associated with pressure slowdowns and
     reversals.  If the CTD velocity is less than 0.25 m/s or the pressure
     is not greater than the previous maximum scan, the scan is omitted.

     BINAVG averages the data into 1 db bins.  Each bin is centered around
     a whole pressure value, e.g. the 1 db bin averages scans where pressure
     is between 0.5 db and 1.5 db.

     DERIVE uses 1 db averaged pressure, temperature, and conductivity to
     compute salinity, theta, sigma-t, sigma-th, and dynamic height.

     SPLIT removes decreasing pressure records and keeps only the downcast
     data.

     TRANS converts the data file from binary to ASCII format.  These 
     data are transfered to the PMEL VAX.

     PMEL program GP595_EPIC applies post-cruise conductivity calibration 
     coefficients, recomputes the derived variables in DERIVE, and converts
     the ASCII data files to EPIC format.  Sea-Bird .CNV files are editted 
     to remove bad records near the surface (typically the top 4 m) and any 
     causing spikes in the deeper water column before running GP595_EPIC.
     GP595_EPIC extrapolates raw data to the surface (0 db) within 10 db.  
     Because the SBE module LOOPEDIT does not handle package slowdowns and 
     reversals well in the thermocline where gradients are large, GP595_EPIC 
     removes raw data records where a sigma-theta inversion is greater than 
     -0.01 kg/m3.  Data are linearly interpolated such that a record exists
     for every 1 db.  When data are interpolated over greater than 2 db, the 
     WOCE quality word is '666'.

     PMEL program CALMSTR5 applies post-cruise conductivity calibration
     coefficients and recomputes the derived variables in ROSSUM.  EPICBOMSTR
     converts the ASCII bottle data file into individual cast EPIC data files.
     Bad bottles that were not included in EPIC bottle files were cast 10
     bottle 12.

     Final CTD and bottle files were moved to DISK$EPIC1:[HAYES.DATA] and 
     included in the RIM data management tables on August 20, 1996.  
