


     GP8-01-RB
     NOAA Ship Ronald H. Brown
     Arica, Chile - Panama City, Panama
     October 29 - December 5, 2001

     Chief Scientist: Mr. Brian Lake
     Survey Department: CST Jonathan Shannahoff
     CTD Personnel: CST, Mike Ronanye, Miri Skoriak (salinities)
     Final Processing: K. McTaggart


     ACQUISITION: 

     Sixty-six CTD profiles were collected on this cruise.  Twenty-seven
     profiles were collected from 8S to 12N along 110W.  Twenty-nine profiles
     were collected from 12N to 8S along 95W.  And ten profiles were collected
     along the ship's trackline to Panama. Eight casts were deep (3000 m),
     and the rest were to 1000 m. 

     PMEL's Sea-Bird 9plus CTD s/n 09P8431-0315 measuring pressure (s/n
     53960), temperature sensors (s/n 1370, 1455), and conductivity sensors
     (s/n 1180, 1177) were used for all casts.

     The CTD was mounted in a custom 24-bottle frame with Sea-Bird rosette
     sampler s/n 163.  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 v1.10) 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:

     6 samples were taken each cast, except for the last 10 where only 3 samples
     were taken each cast.  During deep casts, two bottles were tripped at depth
     and a sample taken from each.  Salinity analysis was performed using Guildline
     Autosal 8400B salinometer s/n 61.668 (aka Dallas) and new Ocean Scientific
     International Autosal computer interface, ACI2000.  IAPSO standard seawater
     batch #P139 (Nov, 2000) was used for all casts.  Analysis was performed by
     CST Shannahoff and ABS Miri Skoriak.  Laboratory operating temperature 24
     degrees Celsius.  Only two samples could not be accounted for, one from cast
     0201 and one from cast 0411.  Salinity run containing casts 0201-0221 is 
     extremely salty.

     Excel worksheets of all salinity runs were merged into one and an average
     salinity value for each bottle computed post-cruise.  The reformatted file
     is called ALLSALT.TXT.


     POST-CRUISE CONDUCTIVITY CALIBRATIONS:

     Data were acquired at sea with the wrong configuration set up in the .CON
     file.  TAO1.CON listed primary TC pair to be T1455 and C1177, and secondary
     TC pair to be T1370 and C1180.  Actually, these pairs were the reverse on 
     the underwater package.  Post-cruise, TAO2.CON with the correct configuration
     was used to reprocess all the casts.

     Post-cruise calibrations from Sea-Bird showed that T1370 had drifted by 
     about 1 mdeg before the cruise.  Because this trajectory was much faster than
     T1455, it was decided to calibrate and reduce the secondary data.  GP801S.CAL
     was created post-cruise using SBECAL and ADDSAL programs.  

     Final pressure and temperature calibrations were pre-cruise.  A viscous
     heating correction of -0.0006 C and a historical drift correction of
     zero was applied to temperature sensor s/n 1455.  

     Conductivity fit coefficients were determined using Matlab program
     CALCOS1.  CALCOP programs did not better the fit.

                         number of points used   259
                         total number of points  347
                         % of points used in fit 74.64
                         fit standard deviation  0.002488
                         fit bias               -0.013317874
                         min fit slope           1.0003299
                         max fit slope           1.0003988

     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. 


     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.

     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. 

     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.

     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.

     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.

     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.

     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).  There is no
     bottle file for casts 0171 (CTD bad), 0201, 0211, and 0221.  The following
     bottles were flagged as bad and omitted from their bottle files: cast 
     7 sample 104, cast 11 sample 103, cast 14 103, cast 27 109, cast 31 111,
     cast 40 109, cast 42 109, cast 45 samples 101 and 102, cast 51 105, cast
     53 102, and cast 65 109.

     Final CTD and bottle files were moved to DISK$EPIC1:[HAYES.DATA.GP801.CTD] 
     and included in the MySQL data management tables on January 28, 2002.
