Metadata Report for BODC Series Reference Number 1030343
Metadata Summary
Problem Reports
Data Access Policy
Narrative Documents
Project Information
Data Activity or Cruise Information
Fixed Station Information
BODC Quality Flags
Metadata Summary
Data Description |
|||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||
Data Identifiers |
|||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||
Time Co-ordinates(UT) |
|||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||
Spatial Co-ordinates | |||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||
Parameters |
|||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||
Problem Reports
No Problem Report Found in the Database
Data Quality Report
Data cycle 559 contained bad time and position information. There was no explanation from the originator as to how this may have occurred. VMADCP data without reliable time and positional information is not usable therefore data cycle 559 was removed from the transferred file.
Data Access Policy
Public domain data
These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.
The recommended acknowledgment is
"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."
Narrative Documents
Instrument Description
A 75 kHz Teledyne RD Instruments Ocean Surveyor (OS75) vessel mounted ADCP was installed on the port drop keel of the James Cook, aligned with the bottom of the hull. The draft of the ship is 6.9 m and when lowered the keel extends 2.8 m below the hull. The resulting transceiver depths are 6.9 m when the keel is retracted and 9.7 m when the keel is lowered.
RD Instruments- Ocean Surveyor 75kHz Vessel mounted ADCP.
| Long-Range Mode | ||
|---|---|---|
| Vertical Resolution Cell Size3 | Max. Range (m)1 | Precision (cm/s)2 |
| 8m | 520 - 650 | 30 |
| 16m | 560 - 700 | 17 |
| High-Precision Mode | ||
| Vertical Resolution Cell Size3 | Max. Range (m)1 | Precision (cm/s)2 |
| 8m | 310 - 430 | 12 |
| 16m | 350 - 450 | 9 |
1 Ranges at 1 to 5 knots ship speed are typical and vary with situation.
2 Single-ping standard deviation.
3 User's choice of depth cell size is not limited to the typical values specified.
Profile Parameters
- Velocity long-term accuracy (typical): ±1.0%, ±0.5cm/s
- Velocity range: -5 to 9m/s
- # of depth cells: 1 - 128
- Max ping rate: 0.7
Bottom Track
Maximum altitude (precision <2cm/s): 950m
Echo Intensity Profile
Dynamic range: 80dB
Precision: ±1.5dB
Transducer and Hardware
Beam angle: 30°
Configuration: 4-beam phased array
Communications: RS-232 or RS-422 hex-ASCII or binary output at 1200 - 115,200 baud
Output power: 1000W
Standard Sensors
Temperature (mounted on transducer)
- Range: -5° to 45°C
- Precision: ±0.1°C
- Resolution: 0.03°
Environmental
Operating temperature: -5° to 40°C (-5° to 45°C)*
Storage temperature: -30° to 50°C (-30° to 60°C)*
*later instruments have greater range.
Web Page
Further details can be found on the manufacturer's website or in the specification sheet
BODC Processing
The data were provided to BODC in a .mat Matlab file which covered the period from 11:08:27 10/11/2008 to 10:07:28 09/12/2008 when the drop keel was down and the ship was in the study region of interest. The file span covered the period of calibrated data. The data in the .mat files were contained in a structure array, a 3-d matrix and a 1-d matrix. The structure contained the ADCP data, the 3-d matrix contained the time and position data and the 1-d matrix contained the bin depth information. Before the data was processed the data was brought together into one structure array by BODC.
The structure array contained two, 3-d matrices, each representing a different GPS fix. The first gave the time and position of the first GPS fix after the last ping and the second gave the time and position from the last GPS fix before the ping. There was no indication to which was more accurate with any differences at the 5th decimal point on average. The decision was arbitrarily made to use the GPS fix from before the ping.
The data were transferred to NetCDF format by internally generated Matlab code. During the transfer the variables are mapped to unique BODC parameter codes. The parameter mapping can be seen in the table below.
| Originator's variable | BODC generated file variable | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|---|
| OS75_abs_filt_ave.vel(:,1,:); | OS75.veast | m s-1 | Eastward current velocity | LCEWAS01 | cm s-1 | Unit conversion needed. Values are divided by 100. Positive values represent East. |
| OS75_abs_filt_ave.vel(:,2,:); | OS75.vnorth | m s-1 | Northward current velocity | LCNSAS01 | cm s-1 | Unit conversion needed. Values are divided by 100. Positive values represent North. |
| OS75_abs_filt_ave.depth; | OS75.depth | m | Depth of Bin | DBINAA01 | m | - |
| OS75_abs_filt_ave.nav.txy2(3,:); | OS75.lat | Degrees | Latitudinal position of the ship | ALATPM01 | Degrees | Taken from ship's, Applanix POSMV, GPS |
| OS75_abs_filt_ave.nav.txy2(2,:); | OS75.lon | Degrees | Longitudinal position of the ship | ALONPM01 | Degrees | Taken from ship's, Applanix POSMV, GPS |
The data were screened using in-house visualisation software. Data points judged to be suspect were flagged with the appropriate BODC data quality control flag.
Originator's Data Processing
Sampling Strategy
On transit through to and from the Kerguelen Plateau, the keel was retracted to allow for faster streaming. Once the plateau was reached, the keel was lowered and stayed down until the region was vacated. Navigation data was fed directly to the ADCP systems from the Applanix POSMV system.
During JC029 two different settings were used for the OS75 ADCP.
- Narrowband with Bottom Tracking on
- Narrowband with Bottom Tracking off
Transducer depths were adjusted when the keel was lowered and retracted. For both settings bin size was set to 16 m, profiling to 60 bins with a blanking distance at the surface of 8 m. The time between pings was set to 2 seconds.
Processing
The VMADCP was controlled using the proprietary RDI VmDas software, version 1.42. During the cruise the ADCP setup, data logging, preliminary screening, and mapping of beam data onto Earth co-ordinates was done with the VmDas. The final processing was performed after the cruise using a set of Matlab routines. More information on the ADCP on-board processing, setup, and calibrations can be found on page 111 onwards of the cruise report which is accessible through the JC029 metadata Report.
Calibrations
The cruise operated mostly in deep waters so bottom tracking was generally not possible. However, bottom track data was collected on two occasions when the ship was on the shelf. During the first period the swell caused a great deal of ship motion resulting in lower quality data. Given the low number of points in bottom tracking mode, water tracking mode was used to calibrate the entire period with the drop keel lowered in the study region. The calibration does not include the times the keel was retracted and the other times the keel was down. The result of the calibration was: misalignment = -0.1277, amplitude = 1.006196.
After processing the first few sequences (001-008), it was noticed that a misalignment of 9° was present. The misalignment angle was subsequently changed and the above calibration only covers files with this changed setting.
Data was averaged to 2 minute intervals prior to filtering. Once the data had been filtered it was averaged to 30 minutes resulting in the final version.
Note: The cruise report states the VMADCP data were averaged into 10 minute intervals, however, the data were actually averaged into 30 minute intervals. The discrepancy in interval timing was confirmed with the originators
Project Information
Southern Ocean FINEStructure (SOFINE) project document
The Southern Ocean FINEStructure (SOFINE) project was a UK field programme aimed at studying the frictional processes that slow down the Antarctic Circumpolar Current (ACC) and influence the meridional exchange of water masses in the Southern Ocean.
The study investigated the role of sea floor topography in slowing the ACC and driving meridional flow across the Southern Ocean, and the manner in which mesoscale and small scale oceanic phenomena modified water mass properties and affected their movement across the ACC. Specifically, SOFINE set out to:
- Determine the relative importance of oceanic processes associated with large scale (hundreds to thousands of kilometres) and small scale (a few kilometres) sea floor topography in the context of ACC flow rates and water mass exchange.
- Identify the oceanic processes controlling the rate at which water masses are transformed and fluxed across the ACC.
The SOFINE experiment focused on a major meander of the ACC around the northern Kerguelen Plateau in the Indian Ocean. Theories and models of Southern Ocean circulation indicated that this region experienced intensified 'friction' and cross-ACC flow. Fieldwork was undertaken over a 52 day period in November and December 2008, and included hydrographic observations, microcstructure and turbulence measurements, detailed bathymetric surveys and several deployments of floats, drifters and moorings.
SOFINE was funded by the UK Natural Environment Research Council and involved the collaboration of a number of international institutions: the National Oceanography Centre (UK), the University of East Anglia (UK), British Antarctic Survey (UK), Woods Hole Oceanographic Institution (US), the Commonwealth Scientific and Industrial Research Organisation (Australia), the University of Tasmania (Australia) and the Leibniz Institute of Marine Sciences (IFM-GEOMAR) at the University of Kiel (Germany).
For more information please see the official project website at SOFINE
Data Activity or Cruise Information
Cruise
| Cruise Name | JC029 |
| Departure Date | 2008-11-01 |
| Arrival Date | 2008-12-22 |
| Principal Scientist(s) | Alberto C Naveira Garabato (University of Southampton School of Ocean and Earth Science) |
| Ship | RRS James Cook |
Complete Cruise Metadata Report is available here
Fixed Station Information
No Fixed Station Information held for the Series
BODC Quality Control Flags
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
| Flag | Description |
|---|---|
| Blank | Unqualified |
| < | Below detection limit |
| > | In excess of quoted value |
| A | Taxonomic flag for affinis (aff.) |
| B | Beginning of CTD Down/Up Cast |
| C | Taxonomic flag for confer (cf.) |
| D | Thermometric depth |
| E | End of CTD Down/Up Cast |
| G | Non-taxonomic biological characteristic uncertainty |
| H | Extrapolated value |
| I | Taxonomic flag for single species (sp.) |
| K | Improbable value - unknown quality control source |
| L | Improbable value - originator's quality control |
| M | Improbable value - BODC quality control |
| N | Null value |
| O | Improbable value - user quality control |
| P | Trace/calm |
| Q | Indeterminate |
| R | Replacement value |
| S | Estimated value |
| T | Interpolated value |
| U | Uncalibrated |
| W | Control value |
| X | Excessive difference |
