Metadata Report for BODC Series Reference Number 1844187
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
RRS Discovery cruise DY088 navigation quality control report
Position
Improbable ship speeds were highlighted between 01/04/2018 14:50:59 to 15:08 with a ship speed in excess of 10 m/s. BODC removed data for period 14:30 - 15:43 and linearly interpolated to remove the improbable ship speeds observed. (BODC assessment)
The originator highlighted a failure of the Applanix GPS system between 00:20 to 01:55 on 22nd March 2018 where the position and attitude data should be treated with caution. BODC ran a speed check and found no problems with the positional data and so have not flagged this period highlighted by the originator. (BODC assessment)
Bathymetry
The channel has been flagged throughout the cruise where noise in the channel moves away from the baseline bathymetry. (BODC assessment)
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 |
RRS Discovery cruise DY088 navigation instrumentation
Instrumentation
| Manufacturer | Model | Function | Comments |
| Trimble/Applanix | POSMV | DGPS and attitude | Primary source of position. |
| Kongsberg Maritime | Simrad EA640 | Single-beam echo sounder (hull) | Constant sound velocity correction. |
| Kongsberg Maritime | Simrad EM122 | Multi-beam echo sounder (deep) | Corrected for sound velocity. |
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
| Componenet | DGPS | RTK | GPS Outage |
|---|---|---|---|
| Position | 0.5 - 2 m 1 | 0.02 - 0.10 m 1 | <2.5 m for 30 seconds outages, <6 m for 60 seconds outages |
| Roll and Pitch | 0.020° | 0.010° | 0.020° |
| True Heading | 0.020° with 2 m baseline 0.010° with 4 m baseline | - | Drift <1° per hour (negligible for outages <60 seconds) |
| Heave | 5 cm or 5% 2 | 5 cm or 5% 2 | 5 cm or 5% 2 |
POS MV WaveMaster
| Accuracy | DGPS | RTK | GPS Outage |
|---|---|---|---|
| Position | 0.5 - 2 m 1 | 0.02 - 0.10 m 1 | <3 m for 30 seconds outages, <10 m for 60 seconds outages |
| Roll and Pitch | 0.030° | 0.020° | 0.040° |
| True Heading | 0.030° with 2 m baseline | - | Drift <2° per hour |
| Heave | 5 cm or 5% 2 | 5 cm or 5% 2 | 5 cm or 5% 2 |
POS MV Elite
| Accuracy | DGPS | RTK | GPS Outage |
|---|---|---|---|
| Position | 0.5 - 2 m 1 | 0.02 - 0.10 m 1 | <1.5 m for 60 seconds outages DGPS, <0.5 m for 60 seconds outage RTK |
| Roll and Pitch | 0.005° | 0.005° | 0.005° |
| True Heading | 0.025° | 0.025° | Drift <0.1° per hour (negligible for outages <60 seconds) |
| Heave | 3.5 cm or 3.5% 2 | 3.5 cm or 3.5% 2 | 3.5 cm or 3.5% 2 |
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.
RRS Discovery cruise DY088 navigation data processing procedures
Originator's Data Processing
The data were logged by the TECHSAS (TECHnical and Scientific sensors Acquisition System) system into daily NetCDF files. The TECHSAS system is used as the main data logging system on NMF-SS operated reserach vessels. The daily TECHSAS NetCDF navigation and bathymetry files provided to BODC were used for BODC processing. Data were additionally logged into the RVS Level-C format files which have been archived at BODC.
Files delivered to BODC
| Filename | Content description | Format | Interval | Start date/time (UTC) | End date/time (UTC) | Comments |
| yyyymmdd-000000-position-POSMV_GPS.gps | Position (latitude and longitude) (from POSMV) | NetCDF | ~ 1 sec. | 06/03/2018 20:44:12 | 02/04/2018 16:20:41 | - |
| yyyymmdd-000000-gyro-POSMV_GYRO.gyr | True heading (from POSMV Gyro) | NetCDF | ~ 1 sec. | 06/03/2018 20:44:12 | 02/04/2018 16:20:41 | Most accurate source of heading from the ship's gyros |
| yyyymmdd-000000-EA600-EA600_DEPTH.EA600 | Depths from central beam EA640 single-beam echosounder | NetCDF | ~15 seconds | 09/03/2018 12:33:09 | 02/04/2018 16:01:51 | |
| yyyymmdd-000000-sb_depth-EM120_DEPTH.depth | Depths from the EM122 multi-beam echosounder | NetCDF | ~20 seconds | 09/03/2018 10:45:08 | 30/03/2018 22:17:00 |
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BODC Data Processing
Data were banked at BODC following standard banking procedures. Data were averaged to 60 second intervals.
The originator's variables were mapped to appropriate BODC parameter codes as follows:
yyyymmdd-000000-position-POSMV_GPS.gps
| Originator's variable | Originator's units | Description | BODC Code | BODC Units | Unit conversion | Comments |
| measureTS | day since 1899-12-30T00:00:00 UTC | Measure timestamp | Not transferred | |||
| gndspeed | knot | Ground speed | Not transferred. | |||
| gndcourse | Degrees | Ground course | Not transferred. | |||
| alt | meters | Altitude | Not transferred. | |||
| lat | decimal degrees | Latitude north | ALATGP01 | decimal degrees | none | |
| prec | dimensionless | Precision | Not transferred | |||
| lon | decimal degrees | Longitude east | ALONGP01 | decimal degrees | none | |
| Heading | degrees | True heading | Not transferred | |||
| Mode | dimensionless | GPS mode | Not transferred | |||
| time | days since 1899-12-30 00:00:00 UTC | Acquisition time | Not transferred |
yyyymmdd-000000-gyro-POSMV_GYRO.gyr
| Originator's variable | Originator's units | Description | BODC Code | BODC Units | Unit conversion | Comments |
| heading | Degrees true | True heading | HEADCM01 | degrees | none | |
| time | days since 1899-12-30 00:00:00 UTC | acquisition time | Not transferred. |
yyyymmdd-000000-sb_depth-EM120_DEPTH.depth
| Originator's variable | Originator's units | Description | BODC Code | BODC Units | Unit conversion | Comments |
| freq | kHz | Frequency | Not transferred | |||
| snd | meters | sounding | MBANSWCB | meters | none | Multi-beam - Best quality bathymetry channel |
| time | days since 1899-12-30 00:00:00 UTC | acquisition time | Not transferred |
yyyymmdd-000000-EA600-EA600_DEPTH.EA600
| Originator's variable | Originator's units | Description | BODC Code | BODC Units | Unit conversion | Comments |
| DepthF | fathom | Depth in fathoms | Not transferred | |||
| depthm | meters | Depth in meters | MBANZZ01 | meters | none | Single beam |
| depthft | feet | Depth in feet | Not transferred | |||
| time | days since 1899-12-30 00:00:00 UTC | acquisition time | Not transferred |
All the reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag.
Position
A check was run on positional data to identify gaps and improbable values (through the calculation of speed). This check highlighted improbable ship speeds and gaps in data due to a failure of the Applanix GPS system. During BODC processing, the improbable ships speeds were removed and then the gaps were linearly interpolated.
Ship Velocities
Ship velocities were calculated from the main latitude and longitude channels using standard BODC procedures.
GEBCO
GEBCO bathymetry was added to the file using the main latitude and longitude channels.
Distance Run
Distance run was calculated from the main latitude and longitude channels, starting from the beginning of the file, using BODC standard procedures. This created channel - 'DSRNCV01' .
Bathymetry
Bathymetry data were screened independently as well as against GEBCO bathymetry measurements. Bathymetry data from the EM122 multi-beam echo-sounder were deemed to be the best quality. The EM122 used the drop keel-mounted surface sound velocity sensor for calculating sound speed at transducer, and identifying the requirement for taking a new sound velocity profile. Between 00:29 to 01:55 on the 22/03/18 the Seapath330 temporarily provided GPS/Attitude data due to a failure of the Applanix system. The EA640 single-beam was run with a constant sound velocity correction of 1500 ms-1.
Calibration
No field calibrations have been applied.
Project Information
No Project Information held for the Series
Data Activity or Cruise Information
Cruise
| Cruise Name | DY088 |
| Departure Date | 2018-03-07 |
| Arrival Date | 2018-04-02 |
| Principal Scientist(s) | Teal R Riley (British Antarctic Survey) |
| Ship | RRS Discovery |
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 |
