Metadata Report for BODC Series Reference Number 1030355

• Metadata Summary

• Problem Reports

• Data Access Policy

• Narrative Documents

• Project Information

• Data Activity or Cruise Information

• Fixed Station Information

• BODC Quality Flags

• SeaDataNet Quality Flags

Metadata Summary

Problem Reports

No Problem Report Found in the Database

Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."

Narrative Documents

Instrument Description

A 150 kHz Teledyne RD Instruments Ocean Surveyor (OS150) vessel mounted ADCP was installed on the port drop keel of the James Cook. The instrument is situated behind a plate and is approximately 10 cm higher than the OS75 ADCP which is 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 6.8 m when the keel is retracted and 9.6 m when the keel is lowered.

RD Instruments- Ocean Surveyor 150kHz Vessel mounted ADCP.

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: 1.5

Bottom Track

Maximum altitude (precision <2cm/s): 600m

Echo Intensity Profile

Dynamic range: 80dB
Precision: ±1.5dB

Transducer & 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 in the manufacturer's website or in the specification sheet.

Trimble Applanix Position and Orientation Systems for Marine Vessels (POSMV)

The Position and Orientation Systems for Marine Vessels (POSMV) is a real time kinematic (RTK) and differential global positioning system (DGPS) receiver for marine navigation. It includes an inertial system that provides platform attitude information. The instrument provides accurate location, heading, velocity, attitude, heave, acceleration and angular rate measurements.

There are three models of Applanix POSMV, the POS MV 320, POS MV Elite and the POS MV WaveMaster. POS MV 320 and POS MV WaveMaster are designed for use with multibeam sonar systems, enabling adherence to IHO (International Hydrographic Survey) standards on sonar swath widths of greater than ± 75 degrees under all dynamic conditions. The POS MV Elite offers true heading accuracy without the need for dual GPS installation and has the highest degree of accuracy in motion measurement for marine applications.

Specifications

POS MV 320

POS MV WaveMaster

POS MV Elite

¹ One Sigma, depending on quality of differential corrections
² Whichever is greater, for periods of 20 seconds or less

Further details can be found in the manufacturer's specification sheet.

BODC Processing

The data were provided to BODC in a .mat Matlab file which covered the period from 11:12:45 10/11/2008 to 09:41:46 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.

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 three different settings were used for the OS150 ADCP.

• Broadband with Bottom Tracking on
• Narrowband with Bottom Tracking on
• Narrowband with Bottom Tracking off

Transducer depth adjustments were made for when the drop keel was lowered or retracted. The adjustments were as follows. In broadband mode, the bin size was set to 4 m, profiling to 45 bins and the blanking distance at the surface was 6 m. In narrowband mode, the bin size was 8 m, profiling to 60 bins and the blanking distance at the surface was 6 m. The time between pings was 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.

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 = -0.8982, amplitude = 1.008350.

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

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:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: