Metadata Report for BODC Series Reference Number 1030275
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
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Time Co-ordinates(UT) |
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Parameters |
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Problem Reports
No Problem Report Found in the Database
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
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The EM120 supersedes the EM12 and was itself superseded by the EM122 in 2008.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
| Frequency | 12 kHz |
| Maximum ping rate | 5 Hz |
| Range sampling rate | 2 kHz |
| Swath coverage sector | up to 150° |
| Swath width | up to 5.5 x water depth |
| Depth resolution | 10 to 40 cm |
| Depth range | 20 to 11,000 m |
| Pulse length | 2, 5 and 15 ms |
| Number of beams | 191 |
| Beam width | 1° x 1° |
| Beam spacing (at angular coverage) | 1% of depth at 90° |
Further details can be found in the manufacturer's specification sheet.
BODC Data Processing
The data were provided to BODC in as Generic Mapping Tools (GMT) output NetCDF .grd format. In addition to this file, BODC were also provided with the raw xyz file, which is available upon request.
The files provided appeared to have been written with an early version of GMT, using a now deprecated grid file format (cf #10). To solve the issue, the each file was converted to ASCII format from the NetCDF .grd file. The ASCII grid file was then converted back to a GMT NetCDF grid using a current version of GMT. The new file was then transferred, using BODC generated Matlab code, into BODC standard NetCDF format.
During transfer the original variables are mapped to unique BODC parameter codes. The parameter mapping can be seen below.
| Originator's variable | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| x | Degrees | Longitude | ALONZZ01 | Degrees | Eastern values are positive |
| y | Degrees | Latitude | ALATZZ01 | Degrees | Northern values are positive |
| z | Metres | Sea floor depth | MBAN1234 | Metres | - |
During transfer plots of the original files and of the transferred files were produced. These were visually compared to check that the data has transferred correctly. No problems were detected.
Originator's Data Processing
Bathymetry data were collected by a Simrad EM120 multi-beam echo sounder. Details of the sampling and on-board data processing are available in sections 3.1 and 5 of the JR99 cruise report.
Project Information
No Project Information held for the Series
Data Activity or Cruise Information
Cruise
| Cruise Name | JR20030816 (JR99) |
| Departure Date | 2003-08-16 |
| Arrival Date | 2003-08-27 |
| Principal Scientist(s) | Carol J Pudsey (British Antarctic Survey) |
| Ship | RRS James Clark Ross |
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 |
SeaDataNet Quality Control Flags
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
| Flag | Description |
|---|---|
| 0 | no quality control |
| 1 | good value |
| 2 | probably good value |
| 3 | probably bad value |
| 4 | bad value |
| 5 | changed value |
| 6 | value below detection |
| 7 | value in excess |
| 8 | interpolated value |
| 9 | missing value |
| A | value phenomenon uncertain |
| B | nominal value |
| Q | value below limit of quantification |
