LADCP
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The Lowered Acoustic Doppler Current Profiler (LADCP) data were acquired while the Conductivity Temperature Depth (CTD) sensor was in the water during the Australian 2006 V3 BROKE-west survey. Data Acquisition: The LADCP is mounted on the CTD frame and is lowered through the water column from surface to bottom on each CTD cast. During the cast upward and downward facing sensor heads ensonify the water column with four beams per head, collecting the data necessary to calculate the vertical velocity of the LADCP on the CTD frame, as well as the northward and eastward components of the current relative to the LADCP for the entire water column. Once the LADCP has been retrieved, the data collected in the cast are downloaded to a PC as two raw binary .adp files, one for the upward looking head and one for the downward. This occurs for each CTD cast. The only modification to a normal CTD cast procedure for the LADCP is a 5 minute pause within 50 m of the sea floor on the upcast. This gives the downward sensor time to gather enough data for later determination of relative bottom velocity. The shipboard ADCP is a continuous recording device that operates over the duration of the voyage, ensonifying the water column once a second. It operates in a similar way to the LADCP, except that as it is fixed to the ship, it has only a range of approximately 250m deep. The ADCP data are necessary for final LADCP data processing. Similarly shipboard 10 seconds GPS records and CTD pressure data for the period of each cast is required for LADCP data processing. Data Processing: Once collected the upward and downward raw .adp LADCP files are subjected to fairly extensive processing using software written for the Matlab package, to produce the usable .mat data files given by this dataset. This software, written by Sergeui Sokolov (sergeui.sokolov AT csiro.au), and slightly modified for the 2005/06 V3 BROKE-west voyage by Andrew Meijers and Andreas Klocker combines the raw .adp files with the shipboard ADCP data, 10 second ship GPS data and CTD profile data. While the raw LADCP .adp files can be processed alone with minimal CTD data (date, start time, end time, start and end lat and long and max depth), they will only give current velocities relative to the CTDs frames motion. To gain an absolute profile the software identifies bottom and surface reflections, and uses this and ship ADCP and GPS data as boundary conditions for an integration of the velocity shear in the raw .adp files. The end result of processing is velocity in north and south components for each depth over the CTD cast. For more details refer to the above reference (Wijffels, et. al. 2005). Dataset format: The processed LADCP file (AU0603_LADCP_3_to_120.mat) is given in matlab .mat format, and before future processing with properly calibrated ADCP data, should be regarded as preliminary only. All CTD casts for BROKE-West are included, except for casts 1,2 and 119, where the LADCP was not used in the CTD cast. Casts 1 and 2 are not in the dataset, while 119 is represented by NaN (not a number) values. The absence of casts 1 and 2 from the data mean that care should be taken in attributing the data to the correct cast. Column one in each velocity matrix represents cast 3, not 1, and column 2 is cast 4 and so on up to column 118 representing CTD cast 120. On several casts the ADCP data were not available, meaning only part of the LADCP processing could be completed. This occurred for casts 5, 46, 91, 92, and 96, and data given here are unreferenced to a bottom velocity or ship track. Other errors occurred that meant that casts 68 and 115 could not be processed at all, and so data for these casts are represented by NaN values. Casts not present in dataset: 1,2 Casts represented by NaN values: 68,115 and 119 LADCP data created without ADCP input on casts: 5,46,91,92,96 (warning unconstrained values) The matlab variables contained in the file are: bindep: 20 depth levels in meters at which velocity data occurs for each profile. Each row of matrix represents a depth level, each column a CTD cast, ascending from cast 3 to 120. date: Start date of each cast (UT) (year month day) lat: Start latitude of each cast (decimal degrees) lon: Start longitude of each cast (decimal degrees) stationno: Last 3 digits gives the CTD cast number time: Start time of CTD cast (UT) of each cast (hours min sec) u_down: u (eastward) component of velocity in ms-1 for each bindepth and CTD cast, using only downward looking head data u_final: As for u_down but using data from both heads. This is the best estimate of velocity. u_up: As for u_down, but upward looking head data only. v_down: As for u_down, but northward component of velocity v_final: As for u_final, but northward component of velocity v_up: As for u_up, but northward component of velocity zbottom: Bottom depth in meters for each cast (m) Acronyms used: LADCP: Lowered Acoustic Doppler Current Profiler ADCP: Acoustic Doppler Current Profiler CTD: Conductivity Temperature Depth IASOS: Institute of Antarctic and Southern Ocean Studies CSIRO: Commonwealth Scientific and Industrial Research Organisation This work was completed as part of ASAC projects 2655 and 2679 (ASAC_2655, ASAC_2679).
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Oceanographic measurements were conducted in the South Indian Ocean sector during the southern summer of 2002/2003 on Aurora Australis voyage au0304, V4 2002/2003. A total of 64 vertical CTD stations were taken, in a krill survey area in the vicinity of Mawson, and approximately following WOCE I08 meridional transect passing up the western flank of the Kerguelen Plateau and then continuing south across the Princess Elizabeth Trough to the Antarctic continental shelf. Over 1050 Niskin bottle samples were collected using a SeaBird 24 bottle rosette sampler, with samples collected for the analysis of salinity, dissolved oxygen, nutrients, and biological parameters. Full-depth current profile data were collected by either 1 or 2 lowered acoustic Doppler profilers (LADCP) attached to the CTD rosette package. Near surface current data were also collected using a ship mounted ADCP. An array of 8 moorings comprising current meters and thermosalinographs were deployed along the western flank of the Kerguelen Plateau, for the Deep Western Boundary Current Experiment. Ship's underway data, (including bathymetry, met. sensors and sea surface salinity/temperature/fluorescence) are included in the cruise data set; an offset correction was applied to the underway sea surface salinity and temperature data, derived from comparison with near surface CTD data. A summary of all data and important data quality information is presented in the data report. Note that LADCP data are not included here. This work was completed as part of ASAC projects 1250 and 2312. Models of climate change project a decrease in the global ocean overturning circulation, significantly impacting climate and ocean ecosystems. The Deep Western Boundary Current experiment commenced on this voyage aims to measure the northward transport of Antarctic Bottom Water east of the Kerguelen Plateau so that future change in this component of the global thermohaline circulation can be detected.
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Oceanographic measurements were conducted in the vicinity of the Mertz Polynya, encompassing 2 consecutive seasonal cycles from 1998 to 2000. In the southern winter of 1999, a total of 92 CTD/LADCP vertical profile stations were taken, most to within 20 m of the bottom, with 3 laps completed around the boundary of a box adjacent to the Mertz Glacier. Over 700 Niskin bottle water samples were collected for the measurement of salinity, dissolved oxygen, nutrients, oxygen 18, dimethyl sulphide, and biological parameters, using a 12 bottle rosette sampler mounted on a 24 bottle frame. Additional CTD vertical profiles were taken in April 1998, July 1998 and February 2000. Near surface current data were collected on all cruises using ship mounted ADCP. Two mooring arrays comprising thermosalinographs, current meters and upward looking sonars were deployed in the region of the Polynya. The first array of 7 moorings was deployed in April 1998. The second array of 4 moorings was deployed in the winter of 1999. All 11 Polynya moorings were recovered in February 2000. A summary of all data and data quality is presented in the data report. This work was completed as part of ASAC projects 2223 and 189.
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Oceanographic measurements were conducted in the Southern Ocean Indian sector during the southern summer of 2004/2005 on Aurora Australis voyage au0403, V3 2004/2005. Data were collected during a complete occupation of CLIVAR meridional section I9S; and then along a transect up the northeastern flank of the Kerguelen Plateau, south across the Princess Elizabeth Trough and onward to the Antarctic continental shelf. A total of 115 CTD vertical profile stations were taken, most to within 30 m of the bottom. Over 2450 Niskin bottle water samples were collected for the measurement of salinity, dissolved oxygen, nutrients, CFCs, dissolved inorganic carbon, alkalinity, oxygen-18, methane, selenium and biological parameters, using a 24 bottle rosette sampler. Full depth current profiles were collected by a lowered acoustic Doppler profiler (LADCP) attached to the rosette package, while near surface current data were collected by a ship mounted ADCP. An array of 8 current meter and thermosalinograph moorings, deployed 2 years earlier on cruise au0304, were recovered from the vicinity of the Kerguelen Plateau. Ship's underway data (including bathymetry, met. sensors and sea surface parameters) are included in the cruise data set; an offset correction was applied to the underway sea surface salinity and temperature data, derived from comparison with near surface CTD data. A summary of all data and important data quality information is presented in the data report. LADCP data are not included in this data set. This work was completed as part of ASAC projects 2312 and 2572.