Metadata Report for BODC Series Reference Number 1171301

• 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 Kongsberg Simrad EM 120 multibeam echosounder was used throughout the cruise. The swath pinged once every 30 seconds and was capable of full ocean depth survey with a nominal coverage span of 3 to 6 times the water depth. The echo returned to the receiver on the hull was processed by the transceiver hardware and the Seafloor Information System (SIS) software and displayed as a track beneath the ship displaying the various heights that each ping was returned. The transmit array was split up into sections that were coded with different frequencies ranging from 11.25 to 12.6 KHz. The system installed was a 1x1, meaning it had 48 TX modules and 16 TX modules. The 1x1 system was the highest resolution of the EM 120 series available at the time. The EM 120 system was fully integrated into the ships systems and did not rely upon any other external references with exception of the Trimble Applanix POSMV global positioning system which provided pitch, heave and roll data which were visible in the time series window and was used in real time by SIS to compensate for the ship's movement when transmitting.

Kongsberg EM120 Multibeam Echosounder

The EM120 is a low frequency (12 kHz) multibeam echosounder with full ocean depth capability designed for bathymetric surveys. It measures water depth by monitoring the travel time of an acoustic signal that is transmitted from the ship, reflected off the seabed and received back at the ship.

The main system units of the EM120 are transducer arrays (separate for reception and transmission), preamplifier unit, transceiver unit and operator unit. Sub-bottom profiling capability is an optional extra. For both transmit and receive arrays standard beamwidth is 1° or 2°, and 4° beamwidth is available for the receive array.

The system has 191 beams with pointing angles automatically adjusted according to achievable coverage or operator defined limits. The beam spacing is normally equidistant, corresponding to 1% of depth at 90° angular coverage, 2% at 120° and 3% at 140°. The transmit fan is split into several individual sectors, each of which is corrected independently for vessel roll, pitch and yaw, which places all soundings on a "best fit" to a line perpendicular to the survey line.

The EM120 supersedes the EM12 and was itself superseded by the EM122 in 2008.

Specifications

Further details can be found in the manufacturer's 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

One processed file in ASCII format without headers was provided by the originator. The data from this file were converted into the BODC internal format using established BODC data banking procedures. The following table shows how the variables within the file were mapped to appropriate BODC parameter codes:

The reformatted data were visualised using Matlab. Quality control flags were applied to the data as necessary and absent data replaced with the appropriate absent data value. During screening, it was noted 7 depth measurements were positioned at 0, 0 degrees which were unrealistic for the study area. Since it was impossible to determine the correct positions, the affected data cycles were deleted.

Originator's Data Processing

Sampling Strategy

The Kongsberg Simrad EM 120 multibeam echosounder was used throughout the cruise, except during VMP deployments and during mooring triangulation when they were turned off. During VMP casts the multibeam echosounder was turned on sporadically to allow the CTD operator to receive a depth for bottom approach.

The EM 120 instrument was updated with sound velocity profiles (SVP) taken at opportune moments during the cruise. In total 6 SVP casts were performed throughout the cruise with some casts being reused when an area was entered where they were taken originally. Further details of the swath system set up including positioning of the transmit and receive transducers can be found in the cruise report from page 178.

Data processing

Raw data files (.all, .ix1 and .ix2) produced by the instrument were processed by MB-System software for a subset of the multibeam data that was relevant to the survey area. The MB-System software processing produced statistic files (.inf) which contained metadata about the multibeam data, fast bathymetry files (.fbt) in format 71 which contained bathymetry data only and fast navigation files (.fnv) in ASCII format which contained navigation data only. The MB-System software files were then converted into text files in order for them to be read without MB-System software. For more information on processing with MB-System software see chapter 4 of the software manual.

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: