


     GP6-04-RB
     NOAA Ship RONALD H. BROWN
     Panama - Arica, Chile
     October 27 - November 30, 2004

     Chief Scientist: Dave Zimmerman
     Survey Department: CST Jonathan Shannahoff
     CTD Personnel: CST Jonathan Shannahoff
     Final Processing: K. McTaggart


     ACQUISITION: 

     Forty-nine CTD profiles were collected during this cruise.  Twenty-
     seven profiles were collected from 8S to 12N along 95W.  Twenty-two
     profiles were collected from 8N to 8S along 110W.  The majority of
     casts were to 1000m, three were deep casts to 3000m.

     PMEL's Sea-Bird 9plus CTD s/n 209 measuring pressure (s/n 53586), temp
     sensors s/n 1455 and 1370, and cond sensors s/n 1177 and 1180 were
     used for all casts.  The .CON file used was 4Oct04.CON.

     The CTD was mounted in a yellow 10-liter 24-bottle frame with PMEL SBE 
     carousel pylon s/n 471.  The CTD data stream was passed through 11plus
     deck unit s/n 367 with factory settings.  Digitized data were sent
     to the ship's designated computer equipped with SBE's SEASAVE Win32
     v5.32 acquisition software.  Calibrated data were displayed in a fixed
     listing and graphical form in real-time, as well as stored in raw form
     on hard disk.  A recycled VCR tape recorded the analog signal each 
     cast.  Raw data files were archived to Zip disk each cast, and CDs
     were returned to PMEL for processing.


     SALINITIES:
   
     No duplicate samples were taken this cruise.  Salinity analysis was 
     performed using Guildline Autosal 8400B salinometer s/n 61.668 for casts
     1-39, and s/n 60.843 for casts 40-49.  Samples were analyzed using Ocean
     Scientific ACI2000, and IAPSO standard seawater batch #P142 for casts
     1-5, #P143 for casts 6-39, and #P144 for casts 40-49.  The bath temper-
     ature was set to 24 degrees Celsius.  This season, only 8 samples will
     be collected per cast instead of 12, and no samples will be collected
     from the half-degree stations between 3N-3S.  Raw data were archived
     along with CTD data on CD.

     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 saved as a space delimited file.


     POST-CRUISE CONDUCTIVITY CALIBRATIONS:

     Primary and secondary data were considered.  Both sensor pairs behaved
     very similarly.  Primary data were chosen for reduction owing to the 
     slower historical drift of temp sensor 1455, and the slightly better
     calibration results of cond sensor 1177.  GP604S.CAL was created at PMEL
     and included all stations, 1-49.     

     Final pressure calibrations were pre-cruise.  A historical drift 
     correction of -0.0007 C, as well as a viscous heating correction of
     -0.0006 C was applied to temp sensor 1455 before calibrating conductivity.

     The best fit for conductivity was determined using CALCOS0 on casts 1-49.

        number of points used   263
        total number of points  302
        % of points used in fit 87.09
        fit standard deviation  0.002407
        fit bias               -0.010671096
        min fit slope           1.0002966
        max fit slope           1.0002966

     Slope and bias correction values were applied to CTD burst data and converted
     directly into netCDF format using CALMSTR and CLB_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, and sigma-theta. Bottle data are used
     to calibrate the CTD sensors 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.  Data were kept within 
     0.01 of the mean.

     FILTER applies a low pass filter to pressure with a time constant of
     0.15 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.

     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 7.0.
 
     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.  There is no surface bin.

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

     TRANS converts the data file from binary to ASCII format.

     Program CNV_EPS1 applies post-cruise temperature corrections and
     conductivity calibration coefficients, as well as any offset to salinity,
     recomputes the derived variables in DERIVE, and converts the ASCII data
     files to netCDF format.  CNV_EPS1 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 15 db.
     Because the SBE module LOOPEDIT does not handle package slowdowns and
     reversals well in the thermocline where gradients are large, CNV_EPS1
     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.

     Two bottles were flagged bad: station 0211 sample 106; and station 0241
     sample 107.

     Final CTD and bottle files were moved to /home/plover/insitu2/DATA/hayes
     /gp604/ctd/ and /bot and included in the MySQL data management tables on
     March 15, 2005.
