


     GP4-01-KA
     NOAA Ship Ka'imimoana
     Kwajalein, Marshall Islands - Honolulu, HI
     July 2-30, 2001

     Chief Scientist: Ms. Margie McCarty
     Survey Department: AST Amy Frank (CST Dennis Sweeney post-cruise inport)
     CTD Personnel: AST Amy Frank (CST Dennis Sweeney post-cruise inport)
     Final Processing: K. McTaggart


     ACQUISITION: 

     Forty-nine CTD profiles were collected on this cruise.  Twenty-three
     profiles were collected from 8N-8S, 165E, and twenty-six profiles were
     collected along 180 from 8S-8N and along the ship's trackline from 8N-12N.
     Four casts were deep (>3500 m) and the rest were to 1000 m.

     PMEL's Sea-Bird 9plus CTD s/n 09P10881-0390 measuring pressure (s/n 
     58950), the ship's temperature (s/n 2027, 2026), and the ship's 
     conductivity (s/n 1537, 1536) was used for 49 casts (PMC24.CON, 
     sensors yearly calibrated prior to GP201).

     The CTD was mounted in a custom 24-bottle frame with Sea-Bird rosette 
     sampler s/n 88.  The CTD data stream was passed through 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 Dell 5133 personal 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 hard 
     disk.  Backups of the raw data were made on CD-ROM and returned to
     PMEL for post-cruise processing.

     CST Sweeney was on medical leave this leg.  Augmenter Amy Frank was 
     responsible for running the stored salts from GP301, and doing CTDs
     and salinities for GP401.
 
 
     SALINITIES:

     For casts 5-12, seawater was collected at only 6 depths and salinity samples 
     drawn while the augmenter caught up on GP301 salinities.  For all other casts,
     12 samples at 12 depths were taken as usual.  Duplicate samples were analyzed
     on a subsequent day from the rest.  Salinity analysis was performed using
     Guildline Autosal 8400B salinometer s/n 61.667 and ACI2000 interface.  IAPSO 
     standard seawater batch #P139, was used for all casts.  Laboratory operating
     temperatures ranged from 22.7 to 26.0 degrees Celsius.


     POST-CRUISE CONDUCTIVITY CALIBRATIONS:

     GP401S.CAL of secondary sensor data (not including any duplicate salts)
     was created post-cruise at the lab.  It's completeness and correctness were 
     scrutinized and ammended where needed.  Primary conductivity sensor s/n
     1537 developed an up/down hysteresis between GP301 and GP401, and also
     displayed a noisier signal.  Therefore it was decided to calibrate and
     process the secondary sensor data (s/n 2026 and 1536).

     Final pressure and temperature calibrations were pre-cruise.  A viscous
     heating correction of -0.0006 C and a historical drift correction of
     -0.00024 was applied to temperature sensor s/n 2026.  

     Conductivity fit coefficients were determined using Matlab program
     CALCOS0.  Although there were four deep stations to >3500 m, there were
     no sample data collected deeper than 1000 m so CALCOP routines were not
     considered.  Also, salinity analysis was poor and jumped around with each 
     run owing to an inexperienced operator so station dependent and higher
     order fits were not considered.  Also, a standard deviation criteria of
     2.3 instead of 2.8 was used running CALCOS0.

                         number of points used   318
                         total number of points  484
                         % of points used in fit 65.7
                         fit standard deviation  0.004209
                         fit bias               -0.0066730881
                         fit slope               1.0001906

     Slope and bias correction values were applied to CTD data and converted
     directly into netCDF format using CNV_EPS; and to bottle file data 
     using CALMSTR and CLB_EPS. An additional offset of -0.006 was applied to
     salinity values after calibration in order to align the deep profiles
     within their historical envelope.


     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.

     Station 0011 had to be recovered from VCR tape, and the downcast was 
     not part of the archived data returned to the lab. Neither was there a
     .BTL file for station 0011.  Sample data for station 0351 could not be
     found in the salinity data archive.  

     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.

     Final CTD and bottle files were moved to DISK$EPIC1:[HAYES.DATA.GP401.CTD] 
     and included in the MySQL data management tables on August 28, 2001.
