


     GP4-95-DI
     NOAA Ship Discoverer
     Kwajalein, Marshall Islands - Honolulu, Hawaii
     April 25 - May 15, 1995

     Chief Scientist: Mr. Hugh Milburn
     Survey Department: CST L. Murray, J. Davis, N. Shoji
     CTD Personnel: Ship's Survey Department
     Final Processing: K. McTaggart, M. O'Haleck


     ACQUISITION: 

     Seventeen CTD profiles were collected during this cruise covering two 
     meridionals.  Nine profiles were collected along 165E from 8N to 5S, and 
     8 profiles were collected along 180W from 8S to 5N.  The majority of 
     casts were to 1000 m; 1 cast was deep (>3000 db).  

     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.


     SALINITIES:

     Salinity analysis was performed using Guildline Autosal salinometers
     s/n 56.119 (last calibrated at NRCC January 25, 1995).  IAPSO standard 
     seawater batch #P114 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.

     Several autosal runs jumped in conductivity by approximately 0.003 mS/cm 
     owing to poor Autosal standardization and fluctuating ambient temperature
     in the Autosal lab space of 3-6 C.  Sample salinities from a run of GP295
     stations 26-30 (SPR95A.CAL stations 59-63) were bad and not included in
     the calibration file.


     POST-CRUISE CONDUCTIVITY CALIBRATIONS:

     SPR95A.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.  GP395 stations 17-22 (SPR95A.CAL stations 82-87) used
     PMC's CTD package and this group was calibrated separately.

     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
     82-87 used PMC's CTD and conductivity calibration coefficients were
     determined using CALCOS1, station-dependent linear fitting routine.

          Stations 1-18:  number of points used   169
			  total number of points  196
			  % of points used in fit 86.22
			  fit standard deviation  0.001077
			  fit bias                -0.0014831927 mS/cm
			  min fit slope (sta 1)   1.0002803
			  max fit slope (sta 18)  1.0003865

	  Stations 19-50:  number of points used   344
			   total number of points  378
			   % of points used in fit 91.01
			   fit standard deviation  0.001792
			   fit bias                -0.011024989 mS/cm
			   min fit slope (sta 50)  1.0005484
			   max fit slope (sta 19)  1.0007496

	  Stations 51-65:  number of points used   95
			   total number of points  117
			   % of points used in fit 81.2
			   fit standard deviation  0.001161
			   fit bias                -0.0088542832 mS/cm
			   min fit slope (sta 51)  1.0004157
			   max fit slope (sta 65)  1.000484

	  Stations 66-81:  number of points used   161
			   total number of points  192
			   % of points used in fit 83.85
			   fit standard deviation  0.00197
			   fit bias                -0.012371588 mS/cm
			   min fit slope (sta 81)  1.0005701
			   max fit slope (sta 66)  1.0007338

	  Stations 82-87:  number of points used   58
			   total number of points  72
			   % of points used in fit 80.56
			   fit standard deviation  0.00104
			   fit bias                -0.012591445 mS/cm
			   min fit slope (sta 82)  1.0005433
			   max fit slope (sta 87)  1.0005563

	  Stations 88-104:  number of points used   167
			    total number of points  204
			    % of points used in fit 81.86
			    fit standard deviation  0.00147
			    fit bias                -0.013652733 mS/cm
			    min fit slope (sta 88)  1.0006917
			    max fit slope (sta 104) 1.0007495
   
     Slope and bias values were applied to CTD data using PMEL Fortran program
     SPR95_EPIC; and to bottle files using CALMSTR.


     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 SPR95_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 SPR95_EPIC.
     SPR95_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, SPR95_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 CALMSTR 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 September 23, 1996.  
