Metadata Report for BODC Series Reference Number 1817012
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 DY054 navigation 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)
Position
Due to large periods of drop outs in the Seapath 350 GPS the applanix gps data was used to determine the ships position during extended (>30 mins) durations. This data was combined with the Seapath 350 data.
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 DY054 navigation instrumentation
Instrumentation
| Manufacturer | Model | Function | Comments |
| Trimble/Applanix | POSMV | DGPS and attitude | Secondary source of position for science. Used as secondary source of GPS at BODC. |
| Kongsberg Seatex | Seapath 350 | DGPS and attitude | Corrected with constant sound velocity of 1500 ms-1 |
| Kongsberg Maritime | Simrad EA640 | Multi-beam echo sounder (hull) | Corrected for constant sound velocity of 1500 m/s. Local sound velocity correction unknown. |
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 DY054 navigation data processing procedures
Originator's Data Processing
Navigation -
As part of the routine daily processing six navigation streams were extracted from TechSAS (attposmv, cnav, gyropmv, gyros, posmvpos, seapos). Note that there is duplicated information among some of the streams. On Discovery, the master position source is usually posmv. However on DY054 posmv frequently failed and contained bad data, so for this cruise our master navigation file is seapos (seapos_dy054_01.nc).
Seapos position information was streamed directly into the CTD and VMADCP units (replacing the posmv data). There was no editing of positional information, except for the removal of any non-monotonic times with the routine mgyr_01.
Finally the "mbest" scripts were edited to generate a master bestnav file from the seaposposition information (mbest_01_seapos, mbest_02_seapos, mbest_03_seapos, mbest_04_seapos). These generate 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. This is the definitive cruise navigation file. In order to avoid the problem of housekeeping variables like distrun across daily files, the bestnav processing is rerun from the start of the cruise each time it is required. There is therefore only ever one master file.
Bathymetry -
The EA640 data were read into mexec directory 'data/sim', and the EM122 data into the mexec directory 'data/em120'. The data were routinely processed within the script m_dy054_daily_processing.m. Daily files of raw data and smoothed data were preserved.
The key stages are:
msim_01 and mem120_01 to read raw data for given day number and discard data outside the depth range 20m to 10000m, then take the median depth in 300 second bins to discard noise.
Input: data/sim/sim_dy054_dnnn_raw.nc
Output: data/sim/sim_dy054_dnnn_smooth.nc
Output: data/sim/sim_dy054_dnnn_edited.nc
The _edited.nc file is an exact copy of the _smooth.nc file, for later use in msimplot.m.
msim_02 cross-merges bathymetric data streams, bringing em120 data into the sim*.nc file.
Input: data/sim/sim_dy054_dnnn_edited.nc
Input: data/em120/em120_dy054_dnnn_edited.nc
Output: data/sim/sim_dy054_dnnn_edited.nc
msim_plot for graphical editing of the data for spike removal. This allows editing of both (sim and em120) data streams since they've already been merged.
Input: data/sim/sim_dy054_dnnn_edited.nc
Output: data/sim/sim_dy054_dnnn_edited.nc - selected values are changed to NaN
Output: data/sim/mplxyed_<time>_sim_dy054_dnnn - records of which values were selected by the user.
Note: it is not necessary to run mem120_plot.m since msim_02 cross-merged the data.
mday_02 to append edited daily files are appended into a single file:
Input: data/sim/sim_dy054_dnnn_edited.nc
Output: data/sim/sim_dy054_01.nc (with em120 as swath_depth)
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.
Files delivered to BODC
| Filename | Content description | Format | Interval | Start date/time (UTC) | End date/time (UTC) | Comments |
| bst_dy054_01.nc | Position (latitude and longitude) (from Seapath 350) and True heading (from POSMV Gyro) | Mstar | 30 seconds | 27/07/2016 00:00:00 | 14/08/2016 23:55:00 | - |
| sim_dy054_01.nc | Depths from central beam EA640 single-beam echosounder | Mstar | 30 seconds | 27/07/2016 08:50:00 | 14/08/2016 23:55:00 | |
| *-*-Applanix_GPS_DY1.gps | Position (latitude and longitude) (from Applanix) | NetCDF | 30 seconds | 27/07/2016 06:33:02 | 16/08/2016 09:30:00 |
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:
bst_dy054_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 | |
| 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_dy054_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 |
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). Due to gaps in the data the applanix gps data was used to determine the ships position during extended (>30 mins) durations. This data was combined with the Seapath 350 data.
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
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.
Calibration
No field calibrations have been applied.
Project Information
UK - Overturning in the Subpolar North Atlantic Programme (UK-OSNAP) Programme
UK-OSNAP is part of an international collaboration to establish a transoceanic observing system in the subpolar North Atlantic. The aim is to quantify and understand the Subpolar Gyre's response to local and remote forcing of mass, heat and freshwater fluxes, within the conceptual framework of the Atlantic Meridional Overturning Circulation (AMOC).
UK-OSNAP is developing a new observing system to provide a continuous record of full-depth, trans-basin mass, heat, and freshwater fluxes. Combining these sustained measurements with innovative modelling techniques will enable the project to characterise the circulation and fluxes of the North Atlantic Subpolar Gyre.
UK-OSNAP is funded by the Natural Environment Research Council (NERC). The project is led by the National Oceanography Centre (NOC) with partners in the University of Liverpool, the University of Oxford and the Scottish Association for Marine Science (SAMS). It is a part of international OSNAP that is led by USA and includes 10 further partner groups in Canada, France, Germany, the Netherlands and China. The project involves fieldwork at sea and model studies.
The OSNAP observing system consists of two legs: one extending from southern Labrador to the southwestern tip of Greenland across the mouth of the Labrador Sea (OSNAP West), and the second from the southeastern tip of Greenland to Scotland (OSNAP East). The observing system also includes subsurface floats (OSNAP Floats) in order to trace the pathways of overflow waters in the basin and to assess the connectivity of currents crossing the OSNAP line.
NERC have added an extension to UK-OSNAP, until October 2024. This will result in the UK-OSNAP-Decade: 10 years of observing and understanding the overturning circulation in the subpolar North Atlantic (2014-2024).
Data Activity or Cruise Information
Cruise
| Cruise Name | DY054 |
| Departure Date | 2016-07-27 |
| Arrival Date | 2016-08-17 |
| Principal Scientist(s) | N Penny Holliday (National Oceanography Centre, Southampton) |
| 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 |
