GP1-95-DI
NOAA Ship Discoverer
San Diego, California - San Diego, California
February 5 - March 2, 1995
Chief Scientist: Mr. Ben Moore
Survey Department: CST L. Murray, J. Davis, N. Shoji
CTD Personnel: M. McCarty, Ship's Survey Department
Final Processing: K. McTaggart, M. O'Haleck
ACQUISITION:
Thirty-four CTD profiles were collected during this cruise covering
two meridionals from 8N to 8S. Eighteen profiles were collected along
95W, and 15 along 110W. The majority of casts were to 1000 m; 8 casts
were deep (>3000 db). A test cast was made at 32N, 117W enroute to the
first station. These data were not processed.
All casts used TAO's Sea-Bird 9plus CTD s/n 09P10881-0390 measuring
pressure (s/n 58950), temperature (s/n 1708), and conductivity (s/n 1467).
The CTD was mounted in a custom 24-bottle frame with a Sea-Bird rosette
sampler. The CTD data stream was passed through a 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 Zenith personal
computer equipped with Sea-Bird's SEASOFT acquisition software (version
4.207) where calibrated data were displayed in graphical form in real-
time, as well as stored in raw form onto the hard disk. Backups of
the raw data were made on 40 Mbyte 1/4" cartridge tapes and returned
to PMEL for post-cruise processing.
SALINITIES:
Salinity analysis was performed using Guildline Autosal salinometers
s/n 56.119 (last calibrated at NRCC January 25, 1995). IAPSO standard
seawater batch #P114 was used for all casts. NRCC calibrations were not
applied to the bottle salinities used to calibrate this data set, only a
drift-during-run linear interpolation correction. Standard operating
temperature was 24 degrees Celsius.
Several autosal runs jumped in conductivity by approximately 0.003 mS/cm
owing to poor Autosal standardization and fluctuating ambient temperature
in the Autosal lab space of 3-6 C. Sample salinities from a run of GP295
stations 26-30 (SPR95A.CAL stations 59-63) were bad and not included in
the calibration file.
POST-CRUISE CONDUCTIVITY CALIBRATIONS:
SPR95A.CAL was created at PMEL using program SBECAL. Anomalous
differences between CTD and bottle salinities were scrutinized.
Bottle salinities were checked against their original log sheets
for typos. GP395 stations 17-22 (SPR95A.CAL stations 82-87) used
PMC's CTD package and this group was calibrated separately.
Final pressure and temperature calibrations were pre-cruise.
Conductivity calibration coefficients were best determined for PMEL's
CTD using a station-dependent second-order fitting routine, CALCOS2,
written by Greg Johnson in MATLAB on the following groups. Stations
82-87 used PMC's CTD and conductivity calibration coefficients were
determined using CALCOS1, station-dependent linear fitting routine.
Stations 1-18: number of points used 169
total number of points 196
% of points used in fit 86.22
fit standard deviation 0.001077
fit bias -0.0014831927 mS/cm
min fit slope (sta 1) 1.0002803
max fit slope (sta 18) 1.0003865
Stations 19-50: number of points used 344
total number of points 378
% of points used in fit 91.01
fit standard deviation 0.001792
fit bias -0.011024989 mS/cm
min fit slope (sta 50) 1.0005484
max fit slope (sta 19) 1.0007496
Stations 51-65: number of points used 95
total number of points 117
% of points used in fit 81.2
fit standard deviation 0.001161
fit bias -0.0088542832 mS/cm
min fit slope (sta 51) 1.0004157
max fit slope (sta 65) 1.000484
Stations 66-81: number of points used 161
total number of points 192
% of points used in fit 83.85
fit standard deviation 0.00197
fit bias -0.012371588 mS/cm
min fit slope (sta 81) 1.0005701
max fit slope (sta 66) 1.0007338
Stations 82-87: number of points used 58
total number of points 72
% of points used in fit 80.56
fit standard deviation 0.00104
fit bias -0.012591445 mS/cm
min fit slope (sta 82) 1.0005433
max fit slope (sta 87) 1.0005563
Stations 88-104: number of points used 167
total number of points 204
% of points used in fit 81.86
fit standard deviation 0.00147
fit bias -0.013652733 mS/cm
min fit slope (sta 88) 1.0006917
max fit slope (sta 104) 1.0007495
Slope and bias values were applied to CTD data using PMEL Fortran program
SPR95_EPIC; and to bottle files using CALMSTR.
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. (MARKSCAN creates a
bottle file if a General Oceanics rosette was used.)
ROSSUM averages the bottle data specified in the DATCNV or MARKSCAN
output and derives salinity, theta, sigma-t, and sigma-th. These
bottle files are transfered to the PMEL VAX where post-cruise
calibrations are computed.
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.
SPLIT removes decreasing pressure records and keeps only the downcast
data.
TRANS converts the data file from binary to ASCII format. These
data are transfered to the PMEL VAX.
PMEL program SPR95_EPIC applies post-cruise conductivity calibration
coefficients, recomputes the derived variables in DERIVE, and converts
the ASCII data files to EPIC format. Sea-Bird .CNV files are editted
to remove bad records near the surface (typically the top 3 m) and any
causing spikes in the deeper water column before running SPR95_EPIC.
SPR95_EPIC extrapolates 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, SPR95_EPIC
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 interpolated over greater than 2 db, the
WOCE quality word is '666'.
PMEL program CALMSTR applies post-cruise conductivity calibration
coefficients and recomputes the derived variables in ROSSUM. EPICBOMSTR
converts the ASCII bottle data file into individual cast EPIC data files.
Bad bottles that were not included in EPIC bottle files were station 15
bottle 7.
Final CTD and bottle files were moved to DISK$EPIC1:[HAYES.DATA] and
included in the RIM data management tables on September 23, 1996.