Metadata Report for BODC Series Reference Number 1030066
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
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
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The EM120 supersedes the EM12 and was itself superseded by the EM122 in 2008.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
A total of 14 .grd files were provided to BODC in NetCDF format. In addition to these files, BODC were also provided with the raw xyz files, which are available upon request. The files were transferred using BODC generated Matlab code into BODC standard NetCDF format.
7 of the files provided appeared to have been written with an older version of Generic Mapping Tools (GMT), using a now deprecated grid file format (cf #10). To solve the issue, these grid files were converted to ASCII format from the NetCDF .grd file. The ASCII grid file was then converted back to a NetCDF grid using a GMT routine _ref.nc being appended to the reformatted grid file.
The following files needed to be converted.
| File name |
|---|
| KJ05_AD_MB |
| KJ05_ERN_MB |
| KJ05_ERS_MB |
| KJ05_GB1_MB |
| KJ05_GB2_MB |
| KJ05_HB_MB |
| KJ05_RB_MB |
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 | - |
Due to the nature of the files, screening via in-house visualisation software was not possible. Instead, during transfer plots of the original files and of the transferred files are produced. These can then be visually compared to check that the data has transferred correctly.
Originator's Data Processing
The SV Kommandor Jack 0105 cruise took place between the 11th July 2005 and the 08th August 2005, around the Northern coast of Scotland. Bathymetry data were collected by a Simrad EM120 multi-beam echo sounder.
Project Information
No Project Information held for the Series
Data Activity or Cruise Information
Cruise
| Cruise Name | KJ0105 |
| Departure Date | 2005-07-11 |
| Arrival Date | 2005-08-08 |
| Principal Scientist(s) | Colin L Jacobs (National Oceanography Centre, Southampton) |
| Ship | Kommandor Jack |
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 |
