Metadata Report for BODC Series Reference Number 1838305
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 DY084 navigation quality control report
Bathymetry
The single beam echo sounder channel has been flagged throughout the cruise where noise in the channel moves away from the baseline bathymetry. Drop outs of zero values were converted to the absent data value. (BODC assessment)
Ship velocities
The ship velocities were subject to spiking at around midnight each day. This may have been caused by issues with logging and the transition between daily navigation files. The data were flagged appropriately. (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 EA640 Single Beam Echosounder
The EA640 single beam echosounder comprises a standard EA600 (fitted with a standard transducer) and an additional, non-standard 10 kHz transducer.
The standard 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.
Specifications for a standard EA600 echosounder
| Maximum Ping rate | 20 Hz |
| Resolution | 1 cm |
| Accuracy | 1 cm at 710 and 200 kHz |
| Operating frequencies | 1 or 2 kHz |
| Single Beam frequencies | 12, 18, 33, 38, 50, 70, |
| Dynamic range | 160 dB |
Further details can be found in the manufacturer's specification sheet for the standard EA600 system.
RRS Discovery cruise DY084 navigation instrumentation
Instrumentation
| Manufacturer | Model | Function | Comments |
| Trimble/Applanix | POSMV | DGPS and attitude | Secondary source of position for science. Used as primary source of GPS at BODC. |
| Kongsberg Maritime | Simrad EA640 | Single-beam echo sounder | The Kongsberg EA600 Single beam hydrographical echo sounder is positioned on the port drop keel. It is run without a sound velocity correction and it's raw uncorrected depth is output to Techsas. The system used a constant sound velocity of 1500 ms-1 throughout the water column to allow it to be corrected for sound velocity in post processing if required. |
| Kongsberg Maritime | Simrad EM122 | Multi-beam echo sounder | The Kongsberg EM120 multi-beam hydrographical echo sounder is positioned on the forward starboard hull. It is run with a sound velocity correction and it's centre beam corrected depth is output to Techsas. Surface sound velocity was continuously provided to the system by the AML MicroX-SV sensor installed on the bottom of the drop keel. |
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 DY084 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-Applanix_GPS_DY1.gps | Position (latitude and longitude) (from POSMV) | NetCDF | ~ 1 sec. | 20/09/2017 08:45:00 | 05/11/2017 12:07:00 | - |
| yyyymmdd-000000-gyro-GYRO1_DY1.gyr | True heading (from POSMV Gyro) | NetCDF | ~ 1 sec. | 20/09/2017 08:45:00 | 06/11/2017 10:07:00 | Most accurate source of heading from the ship's gyros |
| yyyymmdd-000000-EA600-EA640_DY1.EA600 | Depths from central beam EA640 single-beam echosounder | NetCDF | <1 second | 21/09/2017 08:13:00 | 05/11/2017 12:07:00 | |
| yyyymmdd-000000-sb_depth-EM120_DY1.depth | Depths from the EM122 multi-beam echosounder | NetCDF | ~15 sec. | 12/10/2017 14:00:00 | 05/11/2017 12:20:00 | Data in the TECHSAS files start later than the single beam echo sounder |
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-Applanix_GPS_DY1.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-GYRO1_DY1.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_DY1.depth
| Originator's variable | Originator's units | Description | BODC Code | BODC Units | Unit conversion | Comments |
| freq | kHz | Frequency | Not transferred | |||
| snd | meters | sounding | Not transferred | |||
| time | days since 1899-12-30 00:00:00 UTC | acquisition time | Not transferred |
yyyymmdd-000000-EA600-EA640_DY1.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). There were two gaps in the positional data at the start and end of the file, produced during loading to the BODC system. These gaps were trimmed after processing was complete.
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.
Bathymetry
Only a small amount of data was provided from the EM122 multi-beam echosounder and therefore has not been transferred. The EA640 single beam echosounder has been carried through. The EA640 single beam echosounder is run without a sound velocity correction and its raw uncorrected depth is output to Techsas.
Calibration
No field calibrations have been applied.
Project Information
No Project Information held for the Series
Data Activity or Cruise Information
Cruise
| Cruise Name | DY084 (AMT27, DY085) |
| Departure Date | 2017-09-23 |
| Arrival Date | 2017-11-05 |
| Principal Scientist(s) | Andrew Rees (Plymouth Marine Laboratory), Phyllis Lam (University of Southampton School of Ocean and Earth Science) |
| 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 |
