


     GP4-02-KA
     NOAA Ship Ka'imimoana
     Kwajalein, Marshall Islands - Honolulu, HI
     July 1-29, 2002

     Chief Scientist: Mr. Andy Shepherd
     Survey Department: ST Jason Poe
     CTD Personnel: ST Jason Poe, Martin Guiles, Andy Shepherd
     Final Processing: K. McTaggart


     ACQUISITION: 

     Fifty-one CTD profiles were collected during this cruise.  Twenty-three
     profiles were collected along 165E from 8N to 8S.  Twenty-eight profiles
     were collected 8S to 12N along 180 and the cruise track to Honolulu.
     The majority of casts were to 1000m; 6 were deep and 2 were to 500 m.

     PMEL's Sea-Bird 9plus CTD s/n 09P10881-0390 measuring pressure (s/n 
     58950), the ship's temperature sensors (s/n 2027, 2026), and conductivity
     conductivity sensors (TAO s/n 1469, ship s/n 1536) were used for casts 1-3.
     Secondary temperature sensor s/n 1708 replaced s/n 2026 for casts 4-18.
     During cast 18, the entire package was lost owing to a break in the cable.
     A backup package was assembled including PMC's CTD s/n 405, temperature
     sensors 2109 and 1710, and conductivity sensors 1725 and 1467.  This 
     configuration was used for casts 19-29.  PMC CTD s/n 439 replaced s/n 
     405 for casts 30-51.

     The CTD was mounted in a custom 24-bottle frame with Sea-Bird rosette 
     sampler s/n 88 for casts 1-18, and s/n 54 for casts 24-29.  Pylon 88 was
     having problems in earlier cruises and failed altogether on cast 29.
     There wasn't a third pylon on board.  The CTD data stream was passed 
     through 11plus deck unit s/n 376 with factory settings.  An analog signal
     was recorded onto the audio portion of VCR tape as a backup for casts 1-23
     only.  The survey tech purposely stopped making VCR backups.  Digitized
     data were sent to a Dell personal computer equipped with Sea-Bird's
     SEASOFT Windows acquisition software where calibrated data were displayed
     in fixed listing  and graphical form in real-time, as well as stored in
     raw form onto hard disk.  Backups of the raw data were made on Zip disk
     and CD-ROM and the CDs were returned to PMEL for post-cruise processing.


     SALINITIES:

     12 samples were taken from casts 1-17 as usual.  No duplicate samples were taken
     this cruise.  Salinity analysis was performed using Guildline Autosal 8400B
     salinometer s/n 61.667, OSI ACI2000 interface, and IAPSO standard seawater
     batch #P139.  Laboratory operating temperature was assumed to be between 22-24
     degrees Celsius.  Raw data were archived on floppy disk.  No processing was
     done on Survey's NT machine.  The original floppy was NOT returned to PMEL in 
     the data package.  .DAT files were emailed to PMEL from Honolulu.

     At PMEL, ACI2000 .dat files were ammended in Excel such that only 1 header line,
     1 standard correction line, and 3 salinity lines per sample were included in
     the file.  Corrected salinity values were fixed to 4 decimal places and the
     file overwritten in the NT folder as a space delimited file.


     POST-CRUISE CONDUCTIVITY CALIBRATIONS:

     GP402S.CAL of secondary sensor data for casts 1-17 
     was created at PMEL using revised NT processing procedures.  Primary TC pair
     (s/n 2027, 1469) were less noisy and used in the final processing.

     Final pressure and temperature calibrations were pre-cruise.  A viscous
     heating correction of -0.0006 C and a historical drift correction of -0.0003
     were applied to temperature sensor s/n 2027.

     Conductivity fit coefficients were determined using Matlab program
     CALCOS0.

                         number of points used   183
                         total number of points  202
                         % of points used in fit 90.59
                         fit standard deviation  0.005834 
                         fit bias               -0.014590693
                         min fit slope           1.0006107
                         max fit slope           1.0006107

     Slope and bias correction values were applied to CTD data and converted
     directly into netCDF format.  It was determined by comparison of deep cast
     0161 at 2S, 165E with historical profiles that an additional salinity
     offset of -0.0042 be applied to casts 1-18 using CNV_SHIFT_EPS; and to bottle
     file data using CALMSTR and CLB_SHIFT_EPS.


     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.  Both down and up casts
     are processed.

     ROSSUM averages the bottle data specified in the DATCNV output and 
     derives salinity, theta, sigma-t, and sigma-th. Bottle data are used
     to calibrate the CTD post-cruise. 

     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.

     TRANS converts the data file from binary to ASCII format.

     Program CNV_EPS applies post-cruise temperature corrections and
     conductivity calibration coefficients, recomputes the derived variables 
     in DERIVE, and converts the ASCII data files to netCDF format.  CNV_EPS
     skips bad records near the surface (typically the top 3 m) as well as any
     records containing -9.990e-29, and copies back 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, CNV_EPS 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 copied back to 
     the surface, the WOCE quality word is '888'; when interpolated over 
     greater than 2 db, the WOCE quality word is '666'.  The WOCE quality word
     consists of a 1-digit flag for pressure, temperature (ITS-90), and 
     salinity.

     Cast 0091 data need to be replayed from VCR tape at a later date.  At
     this time, only data between 275-818 db were recoverable, and were not
     loaded into the database.  Also, several casts are missing more than 10 db
     of data at the beginning of the profile.  These data were extrapolated back
     to the surface within 20 dbar.**   Casts 0101 and 0471 were despiked at depth.

     It was determined that an additional salinity offset be applied to all casts.
     Historical profiles at deep station sites were used to determine the offsets,
     -0.0042 for casts 1-18 and +0.0091 for casts 19-51.

     Program CALMSTR applies post-cruise temperature corrections and 
     conductivity calibration coefficients and recomputes the derived variables
     in ROSSUM.  CLB_EPS converts the ASCII bottle data file into individual
     cast netCDF data files (excluding those flagged as bad).  CLB_SHIFT_EPS
     was used for this cruise to apply a salinity offset of -0.0042 after
     calibrations to casts 1-18 bottle files.  

     Final CTD and bottle files were moved to /home/plover/insitu2/DATA/hayes
     /gp402/ctd/ and included in the MySQL data management tables on October
     7, 2002.

     ** This was done on 12/23/02 by KEM.
