GP6-02-RB NOAA Ship Ronald H. Brown Panama City - Panama City, Panama October 8 - November 8, 2002 Chief Scientist: Mr. Patrick A'hearn Survey Department: CST Jonathan Shannahoff CTD Personnel: CST Shannahoff, Scott McKeever (salinities) Final Processing: K. McTaggart ACQUISITION: Forty-five CTD profiles were collected during this cruise. Twenty-nine profiles were collected from 12N to 8S along 95W. A shallow cast was taken at approximately 6S, 106.5W after the recovery of the 5S 95W drifter. Then 15 profiles were collected from 8S to 8N along 110W. Three casts were deep (3000 m), 7 were shallow, 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 1455, 1370), and conductivity sensors (s/n 1177, 1180) 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 v5.25) 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: Six samples were taken each cast for the majority of the casts. For 4 casts 12 samples were taken. 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 balloon guy Scot McKeever. Laboratory operating temperature is assumed to have been 24 degrees Celsius. Overall, the data are noisy and considered less stable than the CTD. POST-CRUISE CONDUCTIVITY CALIBRATIONS: Primary and secondary sensors tracked each other well during the cruise. There was no significant difference in calibrating one pair over the other, and so the primary pair were processed. Historically though, primary temperature sensor s/n 1455 has a slower drift rate than s/n 1370. Final pressure and temperature calibrations were pre-cruise. A viscous heating correction of -0.0006 C and a historical drift correction of 0.0002 was applied to temperature sensor s/n 1455. Conductivity fit coefficients were determined using Matlab program CALCOS0. CALCOP programs did not better the fit. number of points used 211 total number of points 240 % of points used in fit 87.92 fit standard deviation 0.003951 fit bias -0.021268544 min fit slope 1.0006256 max fit slope 1.0006256 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. 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. The upcast profile was used for casts 0231, 0261, and 0351 because each was missing the beginning of the downcast profile ranging from 10-150 db. 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). The following bottles were flagged as bad and omitted from their bottle files: cast 2 sample 106, cast 4 sample 106, cast 7 102, cast 10 106, and cast 22 107. Cast 27 sample 107 and cast 40 sample 108 were flagged as questionable. Final CTD and bottle files were moved to /plover/insitu2/DATA/hayes/gp602 and included in the MySQL data management tables on November 27, 2002.