Metadata Report for BODC Series Reference Number 2154356
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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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 EM122 12kHz Multibeam Echosounder
The EM122 is designed to perform seabed mapping to full ocean depth with a high resolution, coverage and accuracy. Beam focusing is applied both during reception and transmission. The system has up to 288 beams/432 soundings per swath with pointing angles, which are automatically adjusted according to achievable coverage or operator defined limits.
This model uses both Continuous Wave and Frequency Modulated sweep pulses with pulse compression on reception, in order to increase the maximum useful swath width. The transmit fan is split in several individual sectors, with independent active steering, in order to compensate for the vessel movements.
In multiplying mode, two swaths per ping cycle are generated, with up to 864 soundings. The beam spacing is equidistant or equiangular and the transmit fan is duplicated and transmitted with a small difference in along track tilt, which takes into account depth coverage and vessel speed, to give a constant sounding separation along track. In high density mode, more than one sounding per beam can be produced, such that horizontal resolution is increased and is almost constant over the whole swath.
The EM122 transducers are modular linear arrays in a Mills cross configuration with separate units for transmit and receive. If used to deliver sub-bottom profiling capabilities with a very narrow beamwidth, this system is known as SBP120 Sub-Bottom Profiler.
The specification sheet can be accessed here Kongsberg EM122.
Specifications
| Operational frequency | 12 Hz |
| Depth range | 20 to 11000 m |
| Swath width | 6 x depth, to approximately 30 km |
| Pulse forms | Continuous Wave and Frequency Modulated chirp |
| Swath profiles per ping | 1 or 2 |
| Sounding pattern | equidistant on bottom/equiangular |
| Depth resolution of soundings | 1 cm |
| Sidelobe suppression | -25 dB |
| Suppression of sounding artefacts | 9 frequency coded transmit sectors |
| Beam focusing | On transmit (per sector) and on reception (dynamic) |
| Swath width control | manual or automatic, all soundings intact even with reduced swath width |
| Motion compensation | |
| Yaw | ± 10° |
| Pitch | ± 10° |
| Roll | ± 15° |
EM122 versions
| System version | 0.5x1 | 1x1 | 1x2 | 2x2 | 2x4 | 4x4 |
| Transmit array (°) | 150x0.5 | 150x1 | 150x1 | 150x2 | 150x2 | 150x4 |
| Receive array (°) | 1x30 | 1x30 | 2x30 | 2x30 | 4x30 | 4x30 |
| No of beams/swath | 288 | 288 | 288 | 288 | 144 | 144 |
| Max no of soundings/swath | 432 | 432 | 432 | 432 | 216 | 216 |
| Max no of swaths/ping | 2 | 2 | 2 | 1 | 1 | 1 |
| Max no of soundings/ping | 864 | 864 | 864 | 432 | 216 | 216 |
JC215 Multibeam Bathymetry: Originator's Data Processing
Sampling Strategy
Kongsberg EM122 multibeam bathymetry data were collected on board RRS James Cook cruise JC215 in June/July 2021. The cruise was conducted to carry out geophysical equipment trials off the continental margin to the southwest of the UK.
Funding was provided by the UK's Natural Environment Research Council (NERC) to National Marine Facilities (NMF) under its National Capability Large Research Infrastructure support.
Data Processing
The data were edited using Caris HIPS software by Tim Henstock and gridded at 100m spacing in a WGS84 Mercator projection. They were exported as longitude-latitude-depth triples and submitted to BODC.
JC215 Multibeam Bathymetry: Processing by BODC
The multibeam bathymetry data from the JC125 trials cruise in the Northeast Atlantic were supplied to BODC as a single 100m gridded ASCII file from the EM122 multibeam echosounder. Datasets were are transferred into a common format, a netCDF subset. The following table shows how the variables within the files were mapped to the appropriate BODC parameter codes:
| Original parameter name | Original Units | BODC Parameter Code | BODC Units | Comments |
|---|---|---|---|---|
| Latitude | Degrees | ALATGP01 | Degrees | - |
| Longitude | Degrees | ALONGP01 | Degrees | - |
| Seafloor height | Metres | MBTHHGHT | Metres | - |
Following transfer, the data are screened visually, using BODC's in-house visualisation software, and any spikes or instrument malfunctions are clearly labelled with quality control flags.
Project Information
No Project Information held for the Series
Data Activity or Cruise Information
Cruise
| Cruise Name | JC215 |
| Departure Date | 2021-06-16 |
| Arrival Date | 2021-07-07 |
| Principal Scientist(s) | Jason Scott (National Marine Facilities Sea Systems) |
| Ship | RRS James Cook |
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 |
