Metadata Report for BODC Series Reference Number 770620


Metadata Summary

Data Description

Data Category Bathymetry
Instrument Type
NameCategories
Simrad EM12 S-120 multibeam echosounder  multi-beam echosounders
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Dr Stuart Cunningham
Originating Organization Southampton Oceanography Centre (now National Oceanography Centre, Southampton)
Processing Status banked
Project(s) Rapid Climate Change Programme
RAPIDMOC
 

Data Identifiers

Originator's Identifier CD170MAR12N
BODC Series Reference 770620
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2005-04-21 01:04
End Time (yyyy-mm-dd hh:mm) 2005-04-21 21:09
Nominal Cycle Interval -
 

Spatial Co-ordinates

Southernmost Latitude 24.16882 N ( 24° 10.1' N )
Northernmost Latitude 25.75443 N ( 25° 45.3' N )
Westernmost Longitude 50.53835 W ( 50° 32.3' W )
Easternmost Longitude 49.67770 W ( 49° 40.7' 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 -
 

Parameters

BODC CODE Rank Units Short Title Title
ACYCAA01 1 Dimensionless Record_No Sequence number
ALATGP01 1 Degrees Lat_GPS Latitude north (WGS84) by unspecified GPS system
ALONGP01 1 Degrees Lon_GPS Longitude east (WGS84) by unspecified GPS system
MBANZZ01 1 Metres BathyDepES_ISL Sea-floor depth (below instantaneous sea level) {bathymetric depth} in the water body by echo sounder
 

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

CD170 Swath Bathymetry Data Quality Report

The reformatted data were not visualised using the in house EDSERPLO software. The data are therefore as supplied and have simply been converted to BODC data format and no guidance as to data quality can be given. The data originators state that data were processed using the Simrad Neptune software using the default editing rules and that the 'occasional isolated bad data point' can be seen on the processed XYZ plots but in general these were adequate for mooring location purposes.

For users who have the appropriate visualisation software the original ASCII files are also available.

For further details please see the cruise report


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 EM12, EM12S and EM12D multibeam echosounders

The EM12 series are low frequency (13 kHz) multibeam echosounders with full ocean depth capability designed for bathymetric surveys. They measure 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 system units of the EM12 are transducer arrays (separate for reception and transmission), sea surface sound velocity sensor, preamplifier unit, transceiver unit, bottom detector unit and operator unit. Additional options include acoustic windows (up to icebreaker strength) and a variety of software for processing, plotting and analysing the data.

The basic model is the EM12S which uses a single array of beams with an angular coverage of 90° and a swath width of 2 times water depth. The EM12S-120 is a version of the EM12S with its angular coverage extended to 120° and a swath width of 3.5 times water depth, which translates to a width increase of 4-5 km in 3000-6000 m of water.

The EM12D uses dual arrays, increasing the coverage sector to 150° and the swath width to 7.4 times the water depth. This version has a typical across-track coverage of 20 km from about 2500 m water depth to full ocean depth (an increase in swath width of approximately 10 km in the 3000-6000 m depth range compared with the EM12S). The EM12D also features an extra set of transducers, preamplifier unit, transceiver unit and bottom detector unit.

The EM12 series was based on the EM100, particularly with regards to the use of interferometric signal processing to determine the transducer-to-sea floor distance for each beam, the principles used to compensate for vessel motion and ray bending effects caused by sound speed variations through the water column, and the operator control and data storage systems. The EM12 was replaced in 2000 by the EM120 which was itself superseded in 2008 by the EM122.

Specifications

Parameter EM12 EM12D EM12S-120
Frequency 13 kHz 13 kHz 13 kHz
Depth coverage 50-11000 m 50-11000 m 50-11000 m
Number of beams 81 162 81
Angular width 150° 150° 120°
Beam width 1.8x3.5° 1.8x3.5° 1.5x3.5°
Swath width up to 3.5 x water depth up to 7.4 x water depth up to 3.5 x water depth
Accuracy 50-60 cm or 0.25 % of depth 50-60 cm or 0.25 % of depth 50-60 cm or 0.25 % of depth
Pulse length

10 ms for deep water

2 ms for shallow water

10 ms for deep water

2 ms for shallow water

10 ms for deep water

2 ms for shallow water

Beam spacing equidistant at 90°, 105°, 120° equidistant at 98°, 114°, 128°, 140°, 150° equidistant at 90°, 105°, 120°

Further details can be found in the manufacturer's product description or the instrument manual .

CD170 Swath Bathymetry BODC Processing

The data were received in ASCII format in 4 files covering areas surveyed as potential mooring sites.

The ASCII files were selected and transferred (using transfer trn403) to QXF format, a BODC-defined subset of NetCDF and BODC's format for 2-dimensional data storage. Null data were set to the appropriate absent data values for the code in the BODC parameter dictionary and flagged 'N', data outside parameter dictionary range flagged 'M' and already flagged data given an 'L' flag.

Transfer Mapping

The following table shows a summary of the variables.

Original Parameter Units BODC Parameter Description BODC Units Comments
lat o ALATGP01 Latitude north (WGS84) by unspecified GPS system o None
lon o ALONGP01 Longitude east (WGS84) by unspecified GPS system o None
depth m MBANZZ01 Sea-floor depth (below instantaneous sea level){bathymetric depth} in the water column by echo sounder m None

CD170 Swath Bathymetry Originator's Data Processing

The Simrad EM12 system was run for one test and four scientific surveys. The process was as follows -

For further details please see the cruise report


Project Information

Rapid Climate Change (RAPID) Programme

Rapid Climate Change (RAPID) is a £20 million, six-year (2001-2007) programme of the Natural Environment Research Council (NERC). The programme aims to improve our ability to quantify the probability and magnitude of future rapid change in climate, with a main (but not exclusive) focus on the role of the Atlantic Ocean's Thermohaline Circulation.

Scientific Objectives

Projects

Overall 38 projects have been funded by the RAPID programme. These include 4 which focus on Monitoring the Meridional Overturning Circulation (MOC), and 5 international projects jointly funded by the Netherlands Organisation for Scientific Research, the Research Council of Norway and NERC.

The RAPID effort to design a system to continuously monitor the strength and structure of the North Atlantic Meridional Overturning Circulation is being matched by comparative funding from the US National Science Foundation (NSF) for collaborative projects reviewed jointly with the NERC proposals. Three projects were funded by NSF.

A proportion of RAPID funding as been made available for Small and Medium Sized Enterprises (SMEs) as part of NERC's Small Business Research Initiative (SBRI). The SBRI aims to stimulate innovation in the economy by encouraging more high-tech small firms to start up or to develop new research capacities. As a result 4 projects have been funded.


Monitoring the Meridional Overturning Circulation at 26.5N (RAPIDMOC)

Scientific Rationale

There is a northward transport of heat throughout the Atlantic, reaching a maximum of 1.3PW (25% of the global heat flux) around 24.5°N. The heat transport is a balance of the northward flux of a warm Gulf Stream, and a southward flux of cooler thermocline and cold North Atlantic Deep Water that is known as the meridional overturning circulation (MOC). As a consequence of the MOC northwest Europe enjoys a mild climate for its latitude: however abrupt rearrangement of the Atlantic Circulation has been shown in climate models and in palaeoclimate records to be responsible for a cooling of European climate of between 5-10°C. A principal objective of the RAPID programme is the development of a pre-operational prototype system that will continuously observe the strength and structure of the MOC. An initiative has been formed to fulfill this objective and consists of three interlinked projects:

The entire monitoring array system created by the three projects will be recovered and redeployed annually until 2008 under RAPID funding. From 2008 until 2014 the array will continue to be serviced annually under RAPID-WATCH funding.

The array will be focussed on three regions, the Eastern Boundary (EB), the Mid Atlantic Ridge (MAR) and the Western Boundary (WB). The geographical extent of these regions are as follows:

References

Baehr, J., Hirschi, J., Beismann, J.O. and Marotzke, J. (2004) Monitoring the meridional overturning circulation in the North Atlantic: A model-based array design study. Journal of Marine Research, Volume 62, No 3, pp 283-312.

Baringer, M.O'N. and Larsen, J.C. (2001) Sixteen years of Florida Current transport at 27N Geophysical Research Letters, Volume 28, No 16, pp3179-3182

Bryden, H.L., Johns, W.E. and Saunders, P.M. (2005) Deep Western Boundary Current East of Abaco: Mean structure and transport. Journal of Marine Research, Volume 63, No 1, pp 35-57.

Hirschi, J., Baehr, J., Marotzke J., Stark J., Cunningham S.A. and Beismann J.O. (2003) A monitoring design for the Atlantic meridional overturning circulation. Geophysical Research Letters, Volume 30, No 7, article number 1413 (DOI 10.1029/2002GL016776)


Data Activity or Cruise Information

Cruise

Cruise Name CD170
Departure Date 2005-04-02
Arrival Date 2005-04-27
Principal Scientist(s)Stuart A Cunningham (Southampton Oceanography Centre)
Ship RRS Charles Darwin

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