


     GP6-03-RB
     NOAA Ship Ronald H. Brown
     Panama City - Panama City, Panama
     October 24 - November 22, 2003

     Chief Scientist: Mr. Ben Moore
     Survey Department: CST Jonathan Shannahoff
     CTD Personnel: CST Shannahoff
     Final Processing: K. McTaggart


     ACQUISITION: 

     Sixty-two CTD profiles were collected during this cruise.  Thirty-nine  
     profiles were collected from 12N to 8S along 95W.  Twenty-three profiles
     were collected from 8S to 8N along 110W.  Six casts were deep (>3000 m),
     twelve were shallow (200 m), and the rest were to 1000 m.

     PMEL's Sea-Bird 9plus CTD s/n 93450-0209 measuring pressure (s/n
     53586), temperature sensors (s/n 1455, 1370), conductivity sensors
     (s/n 1177, 1180), and SBE 43 oxygen sensor (s/n 312) were used for all 
     casts.  Also mounted were a load cell (s/n 1108) and two optical sensors
     installed by the NASA group.

     The CTD was mounted in a yellow 24-bottle frame with PMEL Sea-Bird rosette
     sampler s/n 63.  The CTD data stream was passed through Sea-Bird 11plus
     deck unit s/n 367 (ship's) with factory settings.  An analog signal was
     recorded onto the audio portion of VCR tape as a backup.  Digitized data
     were sent to the ship's Gateway G6-200 personal computer equipped with
     Sea-Bird's SEASAVE for Windows acquisition software (Win32 v5.28) 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
     Zip disks and CD-ROM and returned to PMEL for post-cruise calibration and
     processing.

 
     SALINITIES:

     Twelve samples were taken each cast for the majority of casts.  Two samples
     were taken for each shallow casts.  Only 6 samples were taken for nine casts
     in order to catch up on batches.  Salinity analysis was performed using
     Guildline Autosal 8400B salinometer s/n 61.668 (aka Dallas) and OSI computer
     interface, ACI2000.  IAPSO standard seawater batch P141 (June, 2002) was
     used for all casts.  Analysis was performed by CST Jonathan Shannahoff.
     Laboratory operating temperature is assumed to have been 24 degrees Celsius.


     OXYGENS:

     Oxygen samples were collected and analysed at sea by Jan Kaiser of Princeton.
     The results were provided to PMEL in an Excel spreadsheet email attachment.
     Station, niskin number, and dissolved oxygens in umol/kg were extracted from
     the spreadsheet and used to calibrate the SBE 43 oxygen sensor, s/n 312.
     Where duplicate samples were taken, the concentrations were averaged.  Samples
     noted to have bubbles in them were thrown out.


     POST-CRUISE CONDUCTIVITY CALIBRATIONS:

     Primary sensor data (te 1455, co 1177, ox 312) were calibrated and processed.  
     Final pressure and temperature calibrations were pre-cruise.  A viscous
     heating correction of -0.0006 C was applied to temperature sensor s/n 1455
     (no drift was applied since the sensor was calibrated right before this cruise).

     Conductivity fit coefficients were determined using Matlab program
     CALCOS1 for conductivity s/n 1177 stations 1-52.

                         number of points used   469
                         total number of points  570
                         % of points used in fit 82.28
                         fit standard deviation  0.002944
                         fit bias               -0.017162315
                         min fit slope           1.0006714
                         max fit slope           1.0007877

     Slope and bias correction values were applied to CTD data and converted
     directly into netCDF format using CNV_EPS1_OX; and to bottle file data 
     using CALMSTR and CLB_EPS_OX.  An additional salinity offset of -0.006
     was applied to all the data to bring the deep profiles into the historical
     envelope (baseline CGC94 along 110W).


     POST-CRUISE OXYGEN CALIBRATIONS:

     After looking at the oxygen profiles on the acquisition plots of the deep 
     stations, it was decided that there was significant enough hysteresis between
     the down and the up profiles to warrant using the downcast oxygens for
     calibration.  The process was the same as A16N.  Primary sensor data were
     extracted from the .BTL files using SBECAL1K.f.  Sample salinities were 
     matched to CTD records by station/sample number using ADDSALK.f.  Sample
     oxygen data were matched to CTD records by station/sample number using ADDOXYK.f.
     -9's were used for missing sample salinities and oxygens.  Upcast bottle data
     were matched to downcast profile data by sigma-2 using MATCH_SG2_312K.m.
     Greg's program RUN_OXYGEN_CAL_1.m was used to determine an overall group fit
     with a station dependent slope.  Final coefficients were stored in FINAL.mat
     (roughly, slope=0.32, bias=-0.58, lag=8.6s, tcor=0.0008, pcor=0.0001, and 
     weight=0).  About 89% of the data were used in the fit with a standard 
     deviation of 0.5523 (surprisingly good!).  After examining calibrated up/down
     profiles with bottles overplotted, it was evident that the 8.6s lag was over-
     shooting on both sides of the steep thermocline.  The lag was forced to be
     4.0s when the calibrations were applied and this resulted in more acceptable
     minimums.  There were just too few bottles to contrain the fitting routine. 


     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, as well as primary and secondary temps and conds.  Oxygen
     was carried along as volts.  Optical data were not processed.  Markscan
     was used to determine the start of each profile just beneath the surface.

     ROSSUM averages the bottle data specified in the DATCNV output and 
     derives salinity, theta, and oxygen (umol/kg). Bottle data are used
     to calibrate the CTD post-cruise.  Data were averaged over 8 seconds.

     ALIGNCTD advances secondary conductity by 0.073 seconds.  The deck
     unit does this automatically for primary conductivity.

     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 100
     of the mean (i.e. all data).

     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 both primary and secondary salinity.  

     TRANS converts the data file from binary to ASCII format.

     Program CALCTD_K.m applied a viscous correction to temperature, calcos1
     coefficients to conductivity, and final oxygen coefficients to compute
     oxygen (umol/kg).  Pressure calibrations were pre-cruise.  CALCTD_K.m also 
     computed a calibrated salinity profile.  Deep TS profiles were compared with
     historical profiles, especially along 110W, and it was determined that an
     additional offset of -0.006 was needed to bring the GP603 salinity profiles
     into the historical envelope.  This was also done in CALCTD_K.m.  On Nansen,
     program CNV_EPS1.f converted the calibrated ASCII data files into NetCDF 
     format, filling in the surface to 1 dbar, and computing theta, sigma-t,
     sigma-theta, and dynamic height.  

     Likewise for burst data, program CALCLO_K.m applied post-cruise calibrations
     to the bottle file (.CLB) and Nansen program CLB_EPSO.f converted the data
     into NetCDF format.

     Final CTD and bottle files were moved to /plover/insitu2/DATA/hayes/gp603
     and included in the MySQL data management tables on February 24, 2004.
