Metadata Report for BODC Series Reference Number 790922

• 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

Problem Reports

No Problem Report Found in the Database

RAPID Cruise CD170 Navigation Data Quality Report

Latitude and Longitude

The originator noted that the maximum error in both latitude and longitude of the Trimble 4000 was +/- 5m, which was deemed to be large for differential GPS.

Pitch and Roll

Data in the PTCHGP01 and ROLLGP01 channels is only recorded until 15:12 05/04/2005. There is no indication in the cruise report as to why this data is not recorded for the full length of the cruise.

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

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

Global Positioning Satellite System

A location system of unspecified make or model that determines location on the Earth's surface using the Global Positioning Satellite Network. Angular co-ordinates are given relative to WGS84 CRS. Other parameters such as platform velocity may be derived from this.

RAPID Cruise CD170 Navigation Instrumentation

GPS data were logged from the Trimble 4000 differential GPS, the Glonas GPS, the Ashtech GPS and GPS G12. Ship's gyrocompass readings were also logged.

Single beam bathymetry data were collected throughout the cruise using the ship's fitted Simrad EA500 hydrographic precision echosounder and towed fish echosounder. The fish was deployed just after sailing from Tenerife and was used in preference to the hull-mounted transducer.

RAPID Cruise CD170 Navigation Processing

Data from all instruments were logged to the RVS system. A standard PSTAR best navigation file was updated regularly from the bestnav data stream. The preferred input for bestnav is the Trimble 4000 as it has been found to be more accurate on previous cruises. If there were gaps in the Trimble 4000 data, the bestnav process used other input as necessary in the order Glonass, Ashtech, G12, gyro.

Ship's speed

Ship's speed was converted from knots to m s^-1 by multiplying by 0.5144.

Bathymetry

The bathymetry data were corrected by the originator using Carters tables.

Latitude and Longitude

A program was run which locates any gap in the latitude and longitude channels and checks to ensure that the ship's speed does not exceed 15 knots. No excessive ship speeds were found. There was one 30 second gap in latitude and longitude, which was filled with linear interpolation using the BODC program navint. Distance run was recomputed to create a continuous record.

RAPID Cruise CD170 Sea Surface Hydrography, Meteorology and Navigation

Cruise details

The data series supplied by the originator covers 02/04/2005 to 22/04/2005, which is less than the duration of the cruise.

A full copy of the Metadata report can be found here: CD170

Data Aquisition and Onboard Processing

Onboard processing was carried out on a daily basis and involved running a sequence of executable programs. The initial stage transferred the underway surfmet data into PSTAR from RVS format. Subsequent processing included the calculation of salinity and the merging of the different data streams (heading, bestnav, gyro and ash-gyro). An additional executable was run to determine the true wind speed and direction, taking account of the ship's motion and velocity.

BODC Underway Data Processing Procedures

All sea surface hydrographic, navigation and meteorological data were transferred from Matlab format into BODC internal format (QXF). Reformatting and data calibration was carried out, and is discussed in the individual instrument sections. Each data channel was visually inspected and any spikes or periods of dubious data flagged as suspect using the BODC in house visualisation tool EDSERPLO. The capabilities of the workstation screening software allows all possible comparative screening checks between channels (e.g. to ensure corrected wind data have not been influenced by changes in ship's heading). The system also has the facility of simultaneously displaying the data and the ship's position on a map to enable data screening to take oceanographic climatology into account.

The qxf file then underwent a further step. This involved using Matlab to split the qxf file into three separarte qxf files. One contained data for hydrography, one for meterological data and the final qxf file held the navigation data.

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

• To establish a pre-operational prototype system to continuously observe the strength and structure of the Atlantic Meridional Overturning Circulation (MOC).
• To support long-term direct observations of water, heat, salt, and ice transports at critical locations in the northern North Atlantic, to quantify the atmospheric and other (e.g. river run-off, ice sheet discharge) forcing of these transports, and to perform process studies of ocean mixing at northern high latitudes.
• To construct well-calibrated and time-resolved palaeo data records of past climate change, including error estimates, with a particular emphasis on the quantification of the timing and magnitude of rapid change at annual to centennial time-scales.
• To develop and use high-resolution physical models to synthesise observational data.
• To apply a hierarchy of modelling approaches to understand the processes that connect changes in ocean convection and its atmospheric forcing to the large-scale transports relevant to the modulation of climate.
• To understand, using model experimentation and data (palaeo and present day), the atmosphere's response to large changes in Atlantic northward heat transport, in particular changes in storm tracks, storm frequency, storm strengths, and energy and moisture transports.
• To use both instrumental and palaeo data for the quantitative testing of models' abilities to reproduce climate variability and rapid changes on annual to centennial time-scales. To explore the extent to which these data can provide direct information about the thermohaline circulation (THC) and other possible rapid changes in the climate system and their impact.
• To quantify the probability and magnitude of potential future rapid climate change, and the uncertainties in these estimates.

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:

• A mooring array spanning the Atlantic at 26.5°N to measure the southward branch of the MOC (Hirschi et al., 2003 and Baehr et al., 2004).
• Additional moorings deployed in the western boundary along 26.5°N (by Prof. Bill Johns, University of Miami) to resolve transport in the Deep Western Boundary Current (Bryden et al., 2005). These moorings allow surface-to-bottom density profiles along the western boundary, Mid-Atlantic Ridge, and eastern boundary to be observed. As a result, the transatlantic pressure gradient can be continuously measured.
• Monitoring of the northward branch of the MOC using submarine telephone cables in the Florida Straits (Baringer et al., 2001) led by Dr Molly Baringer (NOAA/AOML/PHOD).

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:

• Eastern Boundary (EB) array defined as a box with the south-east corner at 23.5°N, 25.5°W and the north-west corner at 29.0°N, 12.0°W
• Mid Atlantic Ridge (MAR) array defined as a box with the south-east corner at 23.0°N, 52.1°W and the north-west corner at 26.5°N, 40.0°W
• Western Boundary (WB) array defined as a box with the south-east corner at 26.0°N, 77.5°W and the north-west corner at 27.5°N, 69.5°W

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

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:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: