Metadata Report for BODC Series Reference Number 808674

• 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 CD177 Underway Hydrography - Data Quality Report

• Temperature (Sea surface)

  The start of the sea surface temperature channel is suspect and had been flagged by BODC in accordance with BODC data quality control protocols. The data in these sections is to be treated with caution.

  The suspect section covers data from 18:25 on 12/11/2005 to 11:45 on 13/11/2005

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

Falmouth Scientific Inc. OEM CT sensor

The OEM CT sensor is designed to provide high accuracy conductivity and temperature measurements in a package that can be readily integrated into user systems. The CT sensor relies on an inductively coupled conductivity sensor, with a large inside diameter that eliminates the need for pumps. A high grade Platinum Resistance Thermometer is used to measure temperature.

Sensor specifications are given in the table below. Since 2009 this instrument has been manufactured by Teledyne RD Instruments as a Citadel CT-EK Sensor. More information about the instrument can be found on the Teledyne Citadel specification sheet.

Sensor Specifications

Hydrography instrument details

BODC processing

Multiple PSTAR format files were provided to BODC which contained all the data from the navigation, meteorological and sea surface hydrography sensors.

Data were transferred from PSTAR format into NETCDF files. Matlab was used to perform the transfer following BODC data processing guidelines. Each data channel was visually inspected and any spikes or periods of dubious data were flagged as suspect using the BODC in house visualisation tool EDSERPLO. The capabilities of the workstation screening software allows for possible comparative screening checks between channels.

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

Originator's processing

Ship's position given in the source files is from the Bestnav system. Bestnav uses multiple GPS devices to obtain the most accurate position at any time via a heirarchy of devices. GPS data were logged from the Trimble 4000 differential GPS, the Glonass GPS, the Ashtech GPS and GPS G12. Ship's gyrocompass readings were also logged. 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.

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.

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. Meteorological data were collected and sent, along with thermosalinograph (TSG) system measurements, to the ship's central logging system.

The surface hydrography and thermosalinograph measurements were made by the RSU/UKORS Surfmet system. The depth of the ship's intake is 2.5 m. 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.

There are two instance where the ship docked and so the sea surface sensors were switched off.

The first gap occurs from 11.30 on 18/11/2005 to 18.15 on 19/11/2005

The second gap occurs from 7.00 on 21/11/2005 to 13.15 on 22/11/2005

More information on the cruise and the cruise report can be found in the CD177 metadata report

RAPID Cruise CD177 Underway Hydrography

Each variable in the originator's files is mapped to a unique BODC parameter code. Details of the mapping can be seen below.

Data correction and calibration procedures

• Salinity

  The underway salinity channel was calibrated by the data originator using independent bottle salinity samples drawn from the ship's uncontaminated water supply at 4 hour intervals.

  Calibration was achieved with a combination of PSTAR and Matlab routines. Bottle salinity data (.csv files) were transferred to the ship's Unix system and appended into one file. Salinities were converted back to conductivities and merged with the underway conductivity data using the time variable. The discrete bottle samples with matching salinities were used to compute a salinity difference that was filtered and added to the surface salinities.

• Temperature

  Sea surface temperature was calibrated at BODC against CTD temperature averaged over the top 2.5 m. This resulted in only 5 calibration points, of which one was deemed an outlier, leaving 4. Although this is a small number of points to base a correction upon, the standard deviation of the mean of the offset between CTD and underway temperature was relatively small and applying a mean offset correction seemed reasonable (mean = -0.092, standard deviation = 0.006, n = 4).

  Corrected underway temperature = underway temperature - 0.092

• 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.

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: