Metadata Report for BODC Series Reference Number 1756697
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
Data Description |
|||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||
Data Identifiers |
|||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||
Time Co-ordinates(UT) |
|||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||
Spatial Co-ordinates | |||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||
Parameters |
|||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||
Problem Reports
No Problem Report Found in the Database
RRS Discovery DY052 navigation quality control report
Quality control report
Bathymetry
The 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)
Navigation
No data quality issues concerning navigation were found. (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.
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 DY052 navigation instrumentation
Instrumentation
The following scientific navigational and bathymetric systems were fitted.
| 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 (hull) | Corrected for constant sound velocity of 1500 m/s. Local sound velocity correction unknown. |
On DY052 the EA640 echo sounder was activated when not towing the hydrophone. The EM120 sounder observations were not recorded in TechSAS. Since the echo sounder was only in operation when not towing the hydrophone, most of the data will correspond to time spent stationary at CTD stations.
RRS Discovery DY052 navigation data processing procedures
Originator's Data Processing
Navigation -
As part of the daily processing routine, six navigation streams were extracted from TechSAS (attposmv, cnav, gyropmv, gyros, posmvpos, seapos). The posmvpos is the master position source. There was no editing of positional information, except for the removal of any non-monotonic times. Finally a series of scripts were run to produce the master bestnav file. This uses posmvpos for position, and merges on heading so that there is a complete file containing position, heading, course and speed made good, and distance run. The data are reduced to a 30-second time base and heading is properly vector averaged. In order to avoid the problem of housekeeping variables like distrun across daily files, the bestnav processing is re-run from the start of the cruise each time it is required.
Bathymetry -
On DY052 the EA640 echo sounder was activated when the hydrophone was not being towed. The EM120 sounder observations were not recorded in TechSAS. Since the echo sounder was only in operation when not towing the hydrophone, most of the data will correspond to time spent stationary at CTD stations. As part of the daily processing the bathymetry data from EA640 was cleaned of gross errors. Only spikes widely discrepant with the lower resolution bathymetry were removed. Some ~50m spikes were left in place. The constant magnitude of the spikes suggests that these could be caused by interference from other instruments.
The daily Mstar navigation and bathymetry files provided to BODC were used for BODC processing. Data were additionally logged into the RVS Level-C format files and TECHSAS which have been archived at BODC.
For more detailed information on the Originator's underway data processing, please see the cruise report, p56-62.
Files delivered to BODC
| Filename | Content description | Format | Interval | Start date/time (UTC) | End date/time (UTC) | Comments |
| bst_dy052_01.nc | Position (latitude and longitude) (from POSMV) and True heading (from POSMV Gyro) | Mstar | 30 seconds | 05/06/2016 09:00:00 | 23/06/2016 20:03:00 | - |
| sim_dy052_01.nc | Depths from central beam EA640 single-beam echosounder | Mstar | 30 seconds | 07/06/2016 12:00:00 | 23/06/2016 07:20:00 |
BODC Data Processing
Underway data files were merged into a single file using time as the primary linking key. Data were banked using BODC standard banking procedures. Data were averaged to 60 second intervals.
The originator's variables were mapped to appropriate BODC parameter codes as follows:
bst_dy052_01.nc
| Originator's variable | Originator's units | Description | BODC Code | BODC Units | Unit conversion | Comments |
| time | seconds since 01/01/2016 | Measure timestamp | Not transferred | |||
| Lat | degree_north | Latitude north | ALATGP01 | degree_north | - | |
| lon | degree_east | Longitude east | ALONGP01 | decimal degrees | none | |
| ve | m/s | Ship's eastward velocity | APEWGP01 | cm/s | *100 | Not transferred. BODC derived. |
| vn | m/s | Ship's northward velocity | APNSGP01 | cm/s | *100 | Not transferred. BODC derived. |
| distrun | km | Distance travelled | DSRNCV01 | km | Not transferred. BODC derived. | |
| heading_av | degrees | True heading | HEADCM01 | degrees | ||
| heading_av_corrected | degrees | True heading | Not transferred. No difference in values to heading_av - old legacy variable. |
sim_dy052_01.nc
| Originator's variable | Originator's units | Description | BODC Code | BODC Units | Unit conversion | Comments |
| time | seconds since 01/01/2016 | Measure timestamp | Not transferred | |||
| DepthF | fathom | Depth in fathoms | Not transferred | |||
| depthm | meters | Depth in meters | MBANZZ01 | meters | none | Single beam |
| depthft | feet | Depth in feet | Not transferred |
Screening
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). No gaps or improbable values were identified.
Ship Velocities
Ship velocities were calculated from the main latitude and longitude channels using standard BODC procedures.
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
The echo-sounder used a constant sound velocity of 1500 ms-1 throughout the water column, however, it is not known if this was corrected for local sound velocities. The echo-sounder was turned off while towing the hydrophone. Bathymetry data were screened independently as well as against GEBCO bathymetry measurements.
Calibration
No field calibrations have been applied to the data at BODC.
Project Information
No Project Information held for the Series
Data Activity or Cruise Information
Cruise
| Cruise Name | DY052 |
| Departure Date | 2016-06-07 |
| Arrival Date | 2016-06-24 |
| Principal Scientist(s) | Stefan F Gary (Scottish Association for Marine 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 |
