GP1-02-KA NOAA Ship Ka'imimoana San Diego, CA - Manzanillo, Mexico March 1 - April 4, 2002 Chief Scientist: Mr. Ben Moore Survey Department: AST Amy Frank CTD Personnel: AST Amy Frank, Nuria Ruiz Final Processing: K. McTaggart ACQUISITION: Seventy-five CTD profiles were collected on this cruise. Twenty-eight profiles were collected from 12N to 8S along 110W. Forty-seven profiles were collected from 8S to 12N along 95W. The majority of casts were to 1000 m. Because several moorings had conductivity sensors on them, additional shallow casts were taken for calibration purposes, 18 to 200 m and 3 to 500 m. There were 9 deep casts. PMEL's Sea-Bird 9plus CTD s/n 09P10881-0390 measuring pressure (s/n 58950), the ship's temperature sensors (s/n 2027, 2026), and the ship's conductivity sensors (s/n 1537, 1536) were used for the first 16 casts (last calibrated in January, 2002). Primary conductivity sensor s/n 1537 developed a hairline fracture in the cell and was replaced with TAO sensor s/n 1467 (last calibrated in January, 2002). This configuration was used throughout the rest of the cruise (pmc26.con). The CTD was mounted in a custom 24-bottle frame with Sea-Bird rosette sampler s/n 54 and then 88. The CTD data stream was passed through 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 Dell personal computer equipped with Sea-Bird's SEASOFT Windows acquisition software where calibrated data were displayed in fixed listing and graphical form in real-time, as well as stored in raw form onto hard disk. Backups of the raw data were made on Zip disk and CD-ROM and returned to PMEL for post-cruise processing. SALINITIES: 12 samples were taken each cast as usual. No duplicate samples were taken this cruise. Salinity analysis was performed using Guildline Autosal 8400B salinometer s/n 61.667, OSI ACI2000 interface, and IAPSO standard seawater batch #P139. Laboratory operating temperature ranged between 21-24 degrees Celcius. Salinity analysis was poor. Bottle salinities tended to be salty of the CTD for the entire cruise. POST-CRUISE CONDUCTIVITY CALIBRATIONS: GP102S.CAL of secondary sensor data (not including any duplicate salts) was created at sea during GP202 by K. McTaggart. It's completeness and correctness were scrutinized and ammended where needed. Primary sensors s/n 1537 and 1467 were noisier than the secondary sensors 1536 and 2026. Final pressure and temperature calibrations were pre-cruise. A viscous heating correction of -0.0006 C and a historical drift correction of -0.0009 C were applied to temperature sensor s/n 2026. Conductivity fit coefficients were determined using Matlab program CALCOS0. CALCOP programs were not chosen because of the overall poor quality of sample salinity data. In order not to fit the negative scatter in the residuals owing to salty sample readings, the standard deviation allowable in the fit was 2.2 instead of 2.8. number of points used 404 total number of points 612 % of points used in fit 66.01 fit standard deviation 0.004161 fit bias -0.020318704 min fit slope 1.0006152 max fit slope 1.0006152 Slope and bias correction values were applied to CTD data and converted directly into netCDF format using CNV_SHIFT_EPS*; and to bottle file data using CALMSTR and CLB_SHIFT_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, sigma-t, and sigma-th. Bottle data are used to calibrate the CTD 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. 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. 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). Bottle flagged as questionable were station 13 samples 105 and 107, station 15 101, 29 106, 42 201, 44 103, and 55 204. NOTE: When the 9 deep profiles were compared to historical profiles, it was apparent that the CTD data were too salty. The offsets were averaged and 0.0050 were subtracted from CTD salinities using CNV_SHIFT_EPS and CLB_SHIFT_EPS (in order to compute corrected densities for the files). Final CTD and bottle files were moved to /home/plover/hayes/data/gp102/ctd and included in the MySQL data management tables on May 8, 2002.