Metadata Report for BODC Series Reference Number 2220791

• 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

JC069 Quality Control Report

The bathymetry data were quality controlled as described in the originator's data processing section. The EA600 bathymetry channel only contains 60% data and the EM120 bathymetry channel only contains 55% data. In addition, both of these data channels have been binned to five minutes, compared to the rest of the data channels which were binned to one minute, this has also lead to more gaps in the data. All absent data have been flagged as such.

Data Access Policy

Open 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.

If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:

"Contains public sector information licensed under the Open Government Licence v1.0."

Narrative Documents

JC069 Underway Document

Cruise details

Kongsberg EA600 Single Beam Echosounder

The EA600 is a single beam 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 components of the system are hull-mounted transducers linked to general purpose transceivers (GPTs). Up to four GPTs, each controlling one or more transducers, may be operated simultaneously. The GPT generates a signal, which is transmitted into the water column as an acoustic pulse by the transducer array, and the returning echo is recorded by the GPT. GPTs are in turn linked to a combined display and processor, where adjustments (such as sound-speed corrections) may be applied to the data. Available frequencies span from 12 to 710 kHz, and each GPT may operate at a separate frequency. A variety of transducers is available for water depths up to 11,000 m.

The EA600 stores all data internally but has a USB port which allows the possibility of connecting a CD-ROM/DVD drive to read and write the data. All echo data can be stored as files: bitmap, sample, depth or sidescan data.

In deeper waters, the EA600 supports a multipulse function, allowing for a higher pinger rate. While on passive mode, the pinger is normally attached to a device, with the purpose of tracking and displaying its current depth.

The EA600 replaced the EA500 in 2000.

Specifications

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

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.

DIMES James Cook Cruise JC069 Navigation Instrumentation

The following table shows the navigation instruments used on board the ship and their main roles.

Sperry Marine NAVIGAT X MK 1 digital gyrocompass

A digital gyrocompass for use in marine navigation. The system comprises a gyrosphere supported in fluid, suspended at a single point. The centering pin retaining arrangement can be mounted in an additional gimbal system for high speed applications (Mod 7). The system can drive up to 12 analogue repeaters and has 7 independent serial outputs and 2 dependent 6 steps/° heading outputs. The NAVIGAT X MK1 was the first of the Sperry Marine range of heading sensors, which comprises the NAVIGAT 3000 fibreoptic gyrocompass, the NAVIGAT X MK 1 and the NAVIGAT X MK 2 digital gyrocompasses.

Specifications

Detailed specifications can be found in the manufacturer's data 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.

JC069 Data Processing Procedures

Originator's Data Processing

Data were logged daily by the onboard logging system (TECHSAS). As part of the routine daily processing eight navigation streams were extracted from TECHSAS. Due to the availability of high-quality real time heading from the Applanix POSMVPOS, the Ashtech ADU was a low-priority navigation stream on this cruise, but was maintained in case it was needed at short notice.

The C-Nav stream in TECHSAS was known to have a bug, whereby the minutes in the NMEA (National Marine Electronics Association) message sent by the receiver are stored as the decimal part of the degrees. Although tests in port showed that the C-Nav was the most precise and stable of the navigation sources, the need for correction of data taken directly from TECHSAS provided too many possibilities for error to make it wise to use it in real time. Therefore, the data were logged and corrected, but not otherwise used.

POSMVPOS was used as the master position source with no problems noted during the cruise. The data stream contained no gaps longer than five seconds. Data were transferred from the TECHSAS system and reformatted into Mstar format NetCDF using NOC-generated Mstar processing scripts on a daily basis. Matlab scripts were used to read in all streams and then append them into an accumulating cruise file. A bestnav file was then created, which used POSMVPOS for position and merged on heading so that there was a complete file containing position, heading, course and speed made good, and distance run. The data were reduced to a 30 second time base and heading was vector averaged.

Two sources for bathymetry were processed from TECHSAS files. The EA600 echo sounder was operated throughout the cruise, except when pinging was switched off for Vessel Mounted Profiling (VMP) tracking and mooring communications. Since the drop keels were raised throughout the cruise, data quality was often poor or non-existent when sea state was unfavourable. Matlab scripts were used to read raw data for the day, pick data in depth range 5 to 10000, to discard zeros, take median depth in 300 second bins and to discard noise, followed by manual removal of bad data. Positions were loaded from posmvpos and at approximately five minute intervals. Carter area correction was then applied. A cautious approach to accepting data was adopted, and questionable data were discarded rather than retained. Data were retained in the time period from 31 January 2012 19:35 hours to 18 March 2012 12:05 hours, with 60% of the 5 minute bins during that period having valid depths retained.

Data from the EM120 centre beam were logged in TECHSAS and downloaded in daily files. Matlab scripts were used to read raw data correct for soundspeed variations and take median depth in 300 second bins. They were then manually edited. A cautious approach to accepting data was adopted, and questionable data were discarded rather than retained. Data were retained in the time period 02 February 17:07 hours to 18 March 13:32 hours, with 55% of 5 minute bins having retained depths.

The following files were submitted to BODC:

BODC Data Processing

The Bestnav Mstar file contained 30 second averaged Applanix POSMV GPS data from 29 January 2012 17:33:00 hours to 19 March 03 2012 18:00:30 hours. The latitude, longitude and ship's heading were taken from this file and were reformatted to the internal QXF format via the nearest neighbour method. There was found to be one small gap of 10 minutes between 09 February 2012 17:35:00 hours and 29 February 2012 17:43:59 hours in the latitude and longitude which was linearly interpolated by BODC.

The ship's eastward and northward velocities were calculated from the latitudinal and longitudinal channels using BODC established procedures. The distance travelled was also calculated based upon the latitude and longitude to create a new channel, and the GEBCO bathymetry channel was added using BODC established procedures.

All reformatted data were visualised using the in-house Edserplo software. Suspect data were marked by adding the appropriate quality control flag. Data were provided when the ship was still in port, therefore, the file was trimmed at the beginning to match the cruise start date.

The following tables show how the variables within the file were mapped to appropriate BODC parameter codes:

Bestnav Mstar file

EA600

EM120

Project Information

Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) project document

DIMES is a US/UK field program aimed at measuring diapycnal and isopycnal mixing in the Southern Ocean, along the tilting isopycnals of the Antarctic Circumpolar Current.

The Meridional Overturning Circulation (MOC) of the ocean is a critical regulator of the Earth's climate processes. Climate models are highly sensitive to the representation of mixing processes in the southern limb of the MOC, within the Southern Ocean, although the lack of extensive in situ observations of Southern Ocean mixing processes has made evaluation of mixing somewhat difficult. Theories and models of the Southern Ocean circulation have been built on the premise of adiabatic flow in the ocean interior, with diabatic processes confined to the upper-ocean mixed layer. Interior diapycnal mixing has often been assumed to be small, but a few recent studies have suggested that diapycnal mixing might be large in some locations, particularly over rough bathymetry. Depending on its extent, this interior diapycnal mixing could significantly affect the overall energetics and property balances for the Southern Ocean and in turn for the global ocean. The goals of DIMES are to obtain measurements that will help us quantify both along-isopycnal eddy-driven mixing and cross-isopycnal interior mixing.

DIMES includes tracer release, isopycnal following RAFOS floats, microstructure measurements, shearmeter floats, EM-APEX floats, a mooring array in Drake Passage, hydrographic observations, inverse modeling, and analysis of altimetry and numerical model output.

DIMES is sponsored by the National Science Foundation (U.S.), Natural Environment Research Council (U.K) and British Antarctic Survey (U.K.)

For more information please see the official project website at DIMES

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: