Metadata Report for BODC Series Reference Number 1762224

Metadata Summary

Data Description

Data Category Bathymetry
Instrument Type
Simrad EA500 echosounder  single-beam echosounders
Fugro SeaSTAR 9200-G2 Differential Navigation System receiver  Differential Global Positioning System receivers
Ashtech ADU2 Global Positioning System receiver  NAVSTAR Global Positioning System receivers
Sperry Marine MK37 series gyrocompasses  platform attitude sensors
Trimble 4000DS Global Positioning System receiver  Differential Global Positioning System receivers
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Mr Martin Bridger
Originating Organization National Marine Facilities Sea Systems
Processing Status banked
Project(s) Oceans 2025 Theme 10 SO1:AMT

Data Identifiers

Originator's Identifier D371_PRODQXF_NAV
BODC Series Reference 1762224

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2011-09-29 08:19
End Time (yyyy-mm-dd hh:mm) 2011-11-11 17:59
Nominal Cycle Interval 60.0 seconds

Spatial Co-ordinates

Southernmost Latitude 52.05483 S ( 52° 3.3' S )
Northernmost Latitude 51.50700 N ( 51° 30.4' N )
Westernmost Longitude 67.10200 W ( 67° 6.1' W )
Easternmost Longitude 2.70400 W ( 2° 42.2' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor Depth -
Maximum Sensor Depth -
Minimum Sensor Height -
Maximum Sensor Height -
Sea Floor Depth -
Sensor Distribution -
Sensor Depth Datum -
Sea Floor Depth Datum -


BODC CODE Rank Units Short Title Title
AADYAA01 1 Days Date(Loch_Day) Date (time from 00:00 01/01/1760 to 00:00 UT on day)
AAFDZZ01 1 Days Time(Day_Fract) Time (time between 00:00 UT and timestamp)
ALATGP01 1 Degrees Lat_GPS Latitude north (WGS84) by unspecified GPS system
ALONGP01 1 Degrees Lon_GPS Longitude east (WGS84) by unspecified GPS system
APEWGP01 1 Centimetres per second PlatformVelE_GPS Eastward velocity (over ground) of measurement platform by unspecified GPS system
APNSGP01 1 Centimetres per second PlatformVelN_GPS Northward velocity (over ground) of measurement platform by unspecified GPS system
DSRNCV01 1 Kilometres Cmpval Distance travelled
HEADCM01 1 Degrees Platform_Heading Orientation (horizontal relative to true north) of measurement device {heading}
MBANCT01 1 Metres BathyDepESCartCorr Sea-floor depth (below instantaneous sea level) {bathymetric depth} in the water body by echo sounder and correction using Carter's tables

Definition of Rank

  • Rank 1 is a one-dimensional parameter
  • Rank 2 is a two-dimensional parameter
  • Rank 0 is a one-dimensional parameter describing the second dimension of a two-dimensional parameter (e.g. bin depths for moored ADCP data)

Problem Reports

No Problem Report Found in the Database

AMT RRS Discovery Cruise D371 AMT21 Navigation and Bathymetry Data Quality Document

The navigation data have been through BODC quality control screening. Three gaps of less than ten minutes have been filled by interpolation. Overall the data for the cruise duration appear good.

The bathymetric data have been through BODC quality control screening. There are extensive periods of large-scale noise that hide the real bathymetry in the channel. Where possible some periods have been flagged to remove the noise. Users should use caution when interpreting the bathymetric depth channel.

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 Simrad EA500 bathymetric echosounder

The EA500 is a bathymetric echosounder that can be used in water as deep as 10,000 m. It features triple frequency operation with a separate digitiser for each channel and high transmitted power with an instantaneous dynamic range of 160 dB. The instrument can operate with several pulses in the water simultaneously and has bottom tracking capabilities. A wide range of transducers (single beam, split beam or side-looking) is available and the ping rate is adjustable up to 10 pings per second. The split beam operation measures the athwartships inclination angle of the seabed.

This instrument was introduced in June 1989 and and replaced by the EA 600 in 2000.


Operational range 1, 5, 10, 15, 25, 50, 100, 150, 250, 500, 750, 1000, 2500, 5000 and 10000 m
Phasing 0 to 10000 m in 1 m increments (manual or automatic)
Non saturated instantaneous input range -160 to 0 dB
Output power regulation 0 to 20 dB relative to full power
Noise figure 10 dB
Operating temperature 0 to 55°C
Ping rate max 10 pings per second (adjustable)

Further details can be found in the manufacturer's specification sheet .

AMT RRS Discovery Cruise D371 AMT21 Navigation and Bathymetry Instrument Description Document

Instrument Type
Fugro Seastar 9200 G2 XP Differential GPS
Trimble GPS 4000 DS Surveyor GPS
ASHTECH ADU-2 Altitude Detection Unit GPS
Ship's Gyrocompass Gyro compass
Simrad EA500 Precision Echo Sounder Echosounder

Ashtech Global Positioning System receivers (ADU series)

The ADU series of Global Positioning System (GPS) receivers are designed to give real-time three-dimensional position and attitude measurements. Attitude determination is based on differential carrier phase measurements between four antennas connected to a receiver, providing heading, pitch and roll, along with three-dimensional position and velocity.

The ADU2 model receives information from 48 channels, while the upgraded model (ADU5) uses 56 channels. The ADU5 also features a unique Kalman filter with user selectable dynamic modes to match operating conditions. It also incorporates signals from Satellite Based Augmentation Systems (SBAS) and features an embedded 2-channel 300 kHz beacon receiver for easy differential GPS (DGPS) operations.


Parameter ADU2 ADU5

Operational Temperature range:

-40°C to 65°C
-20°C to 55°C

-40°C to 65°C
-20°C to 55°C

Sampling frequency 5 Hz 5 Hz
Receiver channels 48 56


0.2° rms (dynamic) - 0.4° rms (static)
0.4° rms (dynamic) - 0.8° rms (static)

0.02° to 0.2° rms
0.04° to 0.4° rms

Circular Error Probability:

5.0 m
1.0 m

3.0 m
0.4 to 1.0 m

Further details can be found in the manufacturer's specification sheets for the ADU2 and ADU5 .

Fugro SeaSTAR 9200-G2 Receiver

The SeaSTAR 9200-G2 is a dual frequency (L1/L2) receiver that incorporates global positioning system (GPS) and global navigation satellite system (GLONASS) reception capability while tracking the Fugro L-Band satellite broadcast of Differential Global Satellite Navigation System (DGSNS) corrections. These corrections can also be received via internet, as a backup.

The SeaSTAR 9200-G2 can be used in conjunction with other services as HP (GPS network solution), XP (GPS or orbit and clock solution) and G2 (Composite GPS/GLONASS orbit and clock solution). These are also dual frequency carrier phase solutions, which allows for a decimeter level accuracy.

The 72 channels received by the SeaSTAR include GPS- L1 C/A code and L1/L2/L2C full cycle carrier, GLONASS- L1/L2 full cycle carrier, Satellite Based Augmentation System (SBAS) and the Fugro L-Band service.


Position Accuracy Horizontal Vertical
HP 10 cm (95%) 15 cm (95%)
XP 15 cm (95%) 20 cm (95%)
G2 15 cm (95%) 20 cm (95%)

Further details can be found in the manufacturer's specification sheet .

Sperry Marine MK-37 Gyrocompass

A family of instruments that contain a controlled gyroscope which seeks and aligns itself with the meridian and points to true north. They use the properties of the gyroscope in combination with the rotation of the earth and the effect of gravity. The effects of varying speed and latitude are compensated for by the use of manually operated controls. Models MOD I, MOD O, MOD D, MOD D/E are all with an analog output Step or/and Syncro. MOD VT is the latest model with NMEA Data output as well.

Further specifications for MOD VT can be found in the manufacturer's specification document.

Further information for MOD D/E can be found in the user manual .

Trimble 4000DS Global Positioning System receiver

The Trimble 4000DS Differential Surveyor is similar to the 4000RS (a Maxwell-based receiver that is oriented toward precision positioning applications. It is intended for use as a DGPS base station, generating RTCM-104 corrections). The 4000Ds can apply RTCM-104 corrections to the satellite data it receives in order to generate accurate position fixes in real time.

AMT RRS Discovery Cruise D371 AMT21 Navigation and Bathymetry Processing Procedures Document

Originator's Data Processing

During the cruise there was a dual logging system in place on the RRS Discovery. Data from the various instruments were logged to the RVS Level-C system and also as NetCDF (binary) through the Ifremer Techsas data logging system. The following instruments were logged during the cruise:

1) Fugro Seastar 9200 G2 XP Differential (logged to RVS format as gps_g2)
2) Trimble GPS 4000 DS Surveyor (logged to RVS format as gps_4000)
3) ASHTECH ADU-2 Altitude Detection Unit (logged to RVS format as gps_ash)
4) Chernikeef EM speed log (logged to RVS format as log_chf)
5) Ships Gyrocompass (logged to RVS format as gyro)
6) Simrad EA500 Precision Echo Sounder (logged to RVS format as ea500)

Processing was carried out using the RVS software suite. The following routines were run on the navigation and bathymetry data channels to produce files named after the routine that generated them:
RELMOV - Relmov is the relative motion file for this cruise. This was generated using the ships gyro and ships Chernikeef Log data to extract a movement in a given direction. This was then used by bestnav when and where necessary to calculate fixes if GPS fixes were not available.
BESTNAV - Bestnav uses all 3 GPS Systems logged and creates a best suite stream by providing an as complete account of the ships track as possible. This is done by reading all 3 GPS streams with gps_g2 being primary, gps_4000 as secondary and gps_ash as tertiary. The system looks for gaps of a certain length in the primary and when it finds those gaps it requests that the next gps down fill in the gaps. If no GPS data is available it asks RELMOV to fill in until data is available again. Then the system calculates back over itself to ensure that the extrapolated positions are correct using the GPS data available around the gap.
BESTDRF - Bestdrf is a product of bestnav. When run bestnav uses the relmov data which contains a predicted vn and ve based upon direction and speed through the water. The Bestdrf file is the accurate drift velocity of what actually occurred based on the GPS changes between each record.
PRODEP - Prodep is an automated process that accessed the bestnav position fix data and then uses a pre programmed Carter tables of corrections and corrects the echo sounder data for that given time.

Filename Data type Start Calendar Day Start Time Finish Calendar Day Finish Time Data Interval
relmov RVS Level-C processed 2011-09-28 08:06:50 2011-11-12 14:02:40 10 seconds
bestnav RVS Level-C processed 2011-09-28 08:06:50 2011-11-12 14:02:40 10 seconds
bestdrf RVS Level-C processed 2011-09-28 08:06:50 2011-11-12 14:02:40 10 seconds
prodep RVS Level-C processed 2011-09-28 14:20:16 2011-11-09 13:58:05 variable
gps_g2X RVS Level-C raw 2011-09-28 08:06:47 2011-10-01 15:27:46 1 sec
gps_g2 RVS Level-C raw 2011-10-01 09:34:08 2011-11-11 17:58:42 1 sec
gyroX RVS Level-C raw 2011-09-29 09:04:45 2011-10-02 09:00:06 1 sec
gyro RVS Level-C raw 2011-10-01 09:34:09 2011-11-11 17:59:02 1 sec

BODC Data Processing

The last ~20 days TECHSAS files (except the TSG data) were not saved to the post-cruise archive. TECHSAS files from 23 Oct 2011 to 13 Nov 2011 were missing. The RVS level-C files were confirmed complete by the originator. Since the TECHSAS file record for the cruise was incomplete the RVS Level-C files were chosen for transfer to the BODC underway file.

The bestnav data were initially transferred but over 100 gaps were found in the navigation channels, a number of them substantial (>3 hours). The originator confirmed the Fugro Seastar 9200 G2 XP Differential channels were the most reliable of the three GPS instruments on the vessel. The data streams in the gps_g2 and gyro files were checked and found to be more complete for the cruise. The navigation channels from the gps_g2 and gyro files were loaded in preference to the bestnav channels. A description of the channels present in the files, units, whether they were transferred, BODC parameter code and units, and if a unit conversion was applied during the transfer are detailed in the table below:

gps_g2 Channels Description Units BODC Parameter Code Units Conversion Factor
nbseen number of satellites that can theoretically be seen from the current position - not for transfer - -
nbused number of satellites actually used to compute the position - not for transfer - -
hdop GPS horizontal dilution of precision - not for transfer - -
vdop GPS vertical dilution of precision - not for transfer - -
pdop GPS positional dilution of precision - not for transfer - -
sec time stamp applied by the GPS receiver device rather than the Techsas logger - not for transfer - -
lat Latitude Degrees +ve N ALATGP01 Degrees +ve N *1
lon Longitude Degrees +ve E ALONGP01 Degrees +ve E *1
alt height of the antenna above the reference ellipsoid - not for transfer - -
prec horizontal position precision code - not for transfer - -
mode mode that the GPS was operating in. 0 indicates an invalid fix, 1 a GPS fix and 2 a DGPS fix - not for transfer - -
cog Course over ground = Course made good Degrees True APDAGP01 Degrees True *1
sog Speed over ground = Speed made good knots APSAGP01 m s -1 *0.514
gyro Channels Description Units BODC Parameter Code Units Conversion Factor
heading Ship's heading Degrees true HEADCM01 Degrees true *1
prodep Channels Description Units BODC Parameter Code Units Conversion Factor
uncdepth Raw depth from echosounder m MBANZZ01 - To be dropped after screening m *1
cordepth Depth corrected from Carter's tables m MBANCT01 m *1
cartarea Carter's table area from position - not for transfer - -

The navigation channels were checked using BODC Matlab routine 'navcheck' and three gaps were identified. Each period was less than 10 minutes in duration and using the BODC Matlab routine 'navint' the gaps were filled by interpolation. There were no speed check failures. The latitude and longitude channels were screened by plotting the course on to a map of the Atlantic Ocean. There was no further flagging required.

The north-south (APNSGP01) and east-west (APEWGP01) velocities were then calculated from the latitude and longitude using the BODC Matlab routine 'velcal' and the distance run (DSRNCV01) using the BODC Matlab routine 'disrun'.


No calibrations were applied to the navigation or bathymetry channels by BODC.

Project Information

Oceans 2025 Theme 10, Sustained Observation Activity 1: The Atlantic Meridional Transect (AMT)

The Atlantic Meridional Transect has been operational since 1995 and through the Oceans 2025 programme secures funding for a further five cruises during the period 2007-2012. The AMT programme began in 1995 utilising the passage of the RRS James Clark Ross between the UK and the Falkland Islands southwards in September and northwards in April each year. Prior to Oceans 2025 the AMT programme has completed 18 cruises following this transect in the Atlantic Ocean. This sustained observing system aims to provide basin-scale understanding of the distribution of planktonic communities, their nutrient turnover and biogenic export in the context of hydrographic and biogeochemical provinces of the North and South Atlantic Oceans.

The Atlantic Meridional Transect Programme is an open ocean in situ observing system that will:

The specific objectives are:

The measurements taken and experiments carried out on the AMT cruises will be closely linked to Themes 2 and 5. The planned cruise track also allows for the AMT data to be used in providing spatial context to the Sustained Observation Activities at the Porcupine Abyssal Plain Ocean Observatory (SO2) and the Western Channel Observatory (SO10).

More detailed information on this Work Package is available at pages 6 - 9 of the official Oceans 2025 Theme 10 document: Oceans 2025 Theme 10


Data Activity or Cruise Information


Cruise Name D371 (AMT21)
Departure Date 2011-09-29
Arrival Date 2011-11-13
Principal Scientist(s)Glen A Tarran (Plymouth Marine Laboratory)
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