GP1-96-MB
NOAA Ship Malcolm Baldrige
Rodman, Panama - Hilo, Hawaii
May 3 - 31, 1996
Chief Scientist: Mr. D. Zimmerman
Survey Department: CST D. Sweeney
CTD Personnel: A. Nimersheim, Ship's Survey Department
Final Processing: K. McTaggart, M. O'Haleck
ACQUISITION:
Thirty-six CTD profiles were collected during this cruise covering
two meridionals from 8N to 8S. Nineteen profiles were collected along
95W, and 17 along 110W. The majority of casts were to 1000 m; 5 casts
were deep (3000 db).
All casts used TAO's Sea-Bird 9plus CTD s/n 09P10881-0390 measuring
pressure (s/n 58950), temperature (s/n 1708 or 1710), and conductivity
(s/n 1467). The CTD was mounted in a 12-bottle frame with a Sea-Bird
rosette sampler (s/n 54). The CTD data stream was passed through AOML's
Sea-Bird 11plus deck unit. An analog signal was recorded onto the audio
portion of VCR tape as a backup. Digitized data were sent to a personal
computer equipped with Sea-Bird's SEASOFT acquisition software (version
4.209) 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 Syquest 200 Mbyte tapes and returned to PMEL
for post-cruise processing.
SALINITIES:
Salinity analysis was performed using Guildline Autosal salinometer
s/n ??? (last calibrated ???) and IAPSO standard seawater batch #P129.
Instrument 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.
POST-CRUISE CONDUCTIVITY CALIBRATIONS:
GP196A.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. Station 1 was aborted at 40 db so there were no bottle
data for this cast.
Final pressure and temperature calibrations were pre-cruise.
Conductivity calibration coefficients were best determined using a
station-dependent second-order fitting routine, CALCOS2, written by
Greg Johnson in MATLAB on the following groups.
Stations 2-14: number of points used 117
total number of points 130
% of points used in fit 90
fit standard deviation 0.00191
fit bias 0.0030983449 mS/cm
min fit slope 1.0000148
max fit slope 1.0000252
Stations 15-19: number of points used 44
total number of points 50
% of points used in fit 88
fit standard deviation 0.001934
fit bias 0.0061918306 mS/cm
min fit slope 0.99984193
max fit slope 0.99987277
Stations 20-27: number of points used 58
total number of points 70
% of points used in fit 82.86
fit standard deviation 0.001885
fit bias -0.0020791189 mS/cm
min fit slope 1.0002017
max fit slope 1.0002687
Stations 28-36: number of points used 80
total number of points 88
% of points used in fit 90.91
fit standard deviation 0.002486
fit bias 0.00063163251 mS/cm
min fit slope 1.0000853
max fit slope 1.0001812
Slope and bias values were applied to CTD data using PMEL Fortran program
GP196_EPIC; and to bottle files using CALMSTR1.
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 GP196_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 GP196_EPIC.
GP196_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, GP196_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 CALMSTR1 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 21
bottle 5, station 24 bottle 6, station 30 bottle 5, and station 32 bottle
4.
Final CTD and bottle files were moved to DISK$EPIC1:[HAYES.DATA] and
included in the RIM data management tables on September 30, 1996.