


     GP3-96-KA
     NOAA Ship Ka'imimoana
     Honolulu, HI - Kwajalein, Marshall Islands
     June 19 - July 16, 1996

     Chief Scientist: Mr. Andy Shepherd
     Survey Department: CST Jim Davis
     CTD Personnel: L. Stratton, J. Davis
     Final Processing: K. McTaggart, M. O'Haleck


     ACQUISITION: 

     Twenty-six CTD profiles were collected during this cruise covering 
     two meridionals from 8N to 8S.  Nineteen profiles were collected along 
     180W, and 7 along 165E.  The majority of casts were to 1000 m.  Five casts 
     were deep (>3000 db) and 3 were 500 m calibration casts for TAO moorings.  

     All casts used the ship's Sea-Bird 9plus CTD s/n 09P10493-0405 measuring 
     pressure (s/n 61183), temperature (s/n 2026), and conductivity (s/n 1536).
     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 392) with factory settings.  An analog signal was recorded onto
     the audio portion of VCR tape as a backup.  Digitized data were sent to a 
     computer equipped with Sea-Bird's SEASOFT acquisition software (version
     4.216) 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.
 

     SALINITIES:

     Salinity analysis was performed using Guildline Autosal 8400B salinometer
     s/n 61.383 (last calibrated at NRCC February 13, 1996).  IAPSO standard 
     seawater batch #P127 was used for all casts.  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:

     GP396A.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.  There are no bottle data for station 23 owing to a deck
     unit failure at depth.

     Final pressure and temperature calibrations were pre-cruise.  
     Conductivity calibration coefficients were best determined for PMEL's
     CTD using a station-dependent second-order fitting routine, CALCOS2, 
     written by Greg Johnson in MATLAB on the following groups.  

          Stations 1-17:  number of points used   98
			  total number of points  120
			  % of points used in fit 81.67
			  fit standard deviation  0.001039
			  fit bias -0.00047064486 mS/cm
			  min fit slope  1.0000317
			  max fit slope  1.0001249

	  Stations 18-23:  number of points used   35
			   total number of points  36
			   % of points used in fit 97.22
			   fit standard deviation  0.002003
			   fit bias -0.0064073237 mS/cm
			   min fit slope  1.0002996 
			   max fit slope  1.0004012

     Slope and bias values were applied to CTD data using PMEL Fortran program
     GP396_EPIC; and to bottle files using CALMSTR3.


     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 GP396_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 6 m) and any 
     causing spikes in the deeper water column before running GP396_EPIC.
     GP396_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, GP396_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 CALMSTR3 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.

     Final CTD and bottle files were moved to DISK$EPIC1:[HAYES.DATA] and 
     included in the RIM data management tables on October 1, 1996.  
