Metadata Report for BODC Series Reference Number 679532

• 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

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

WET Labs WETStar Fluorometers

WET Labs WETStar fluorometers are miniature flow-through fluorometers, designed to measure relative concentrations of chlorophyll, CDOM, uranine, rhodamineWT dye, or phycoerythrin pigment in a sample of water. The sample is pumped through a quartz tube, and excited by a light source tuned to the fluorescence characteristics of the object substance. A photodiode detector measures the portion of the excitation energy that is emitted as fluorescence.

Specifications

By model:

All models:

Further details can be found in the manufacturer's specification sheet, and in the instrument manual.

Ashtech G12 Global Positioning System Receiver

The Ashtech G12 Global Positioning System (GPS) uses all-in-view tracking and 12 channels to provide real time three-dimensional positional measurements. It is Differential GPS (DGPS) ready, offering an accuracy of better than 40 cm, position latency better than 50 ms, and exact position latency to millisecond accuracy.

Specifications

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

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.

Specifications

Further details can be found in the manufacturer's specification sheets for the ADU2 andADU5.

SeaTech Transmissometer

Introduction

The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.

Specifications

• Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).
• Beam diameter: 15 mm
• Transmitted beam collimation: <3 milliradians
• Receiver acceptance angle (in water): <18 milliradians
• Light source wavelength: usually (but not exclusively) 660 nm (red light)

Notes

The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.

A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.

Further details can be found in the manufacturer's Manual.

CD159 Underway Instrumentation

Navigation

• Global Positioning Systems (GPS)
• Gyrocompass
• Chernikeeff Electro-Magnetic speed log
• Simrad EA-500 10 kHz echo sounder

Meteorology

All meteorological and light sensors were mounted on the ship's foremast.

Hydrography

Ship's intake was at approximately 2.5 m.

Falmouth Scientific Inc. Ocean Sensor Modules

FSI's individual sensor modules include an Ocean Conductivity Module (OCM), Ocean Temperature Module (OTM) and Ocean Pressure Module (OPM). All three use a low power micro-controller to collect, scale and transmit real-time data via RS-232 or RS-485.

* Higher accuracy available

For further details, see the manufacturer's specification sheet.

CD159 Underway General Processing

UKORS data processing

Data logging and initial data processing were handled by the RVS ABC logging system.

Standard navigation processing was carried out using the relmov and bestnav programs. relmov takes in data from the electro-magnetic (EM) speed log and gyro compass in order to generate a relative motion file. This relative motion file was then combined with one or more fix files by the bestnav program in order to generate a 10 second interval best navigation file, bestnav. The original idea behind bestnav was that it would take infrequent fixes, such as those from older transit satellite systems (typically several hours between fixes), or even fixes manually input from sextant sightings, and then dead-reckon between those fixes. Today, with GPS fixes coming in every second, its dead-reckoning facility is only used for periods when GPS drops out, for instance due to an aurora.

The program prodep was used to correct depth data from the Simrad EA-500 echo sounder for variation of sound velocity in sea water (Carter's tables corrections) and written at 10 second intervals to a file called prodep. Meteorological data were collected through a Vaisala QL150 sensor collector at 1 second intervals, which is then averaged to 30 seconds. Salinity data were derived from temperature and conductivity data logged via the Surfmet system using the protsg program.

The bestnav, prodep, rawsurfmet and protsg ASCII files were submitted to BODC for banking.

BODC processing

Problems with the logging of the data channels in the protsg file meant rawsurfmet was used as the source of all hydrographic data, as well as meteorological variables. The bestnav, prodep and rawsurfmet data files were merged at 30 second intervals using an in-house script (BUDS loadrvs) and transformed into QXF format, a subset of netCDF. Following transfer to QXF, the data were visually screened using the in-house EDSERPLO package.

Navigation

Navigation channels were checked for gaps and improbable speeds. 11 gaps were found, all less than 1 minute duration, which were filled using linear interpolation. No speed check errors were found.

The following unit conversions were made:

• Ship's velocity was converted from knots to cm s^-1 by multiplying by 51.444.
• Ship's speed was converted from knots to m s^-1 by multiplying by 0.5144.

CD159 Underway Hydrography

Hydrography Processing Notes

• Temperature

  There was a problem with the logging of the temperature channels. On occasions during the cruise, data from the hull sensor was logged in the housing sensor channel and vice versa. To correct this, the data were swapped between hull and housing channels for the following cycles: 2963-6011 and 6197-11167. The hull temperature sensor was calibrated with concurrent CTD surface temperature values, averaged over the top 5 m. After exclusion of obvious outliers, 14 values were used to determine a mean offset correction (-0.03086). Residuals of the dataset used for calibration range between -0.059 and 0.036. The root mean square of the residuals is 0.024.

  The correction applied to the temperature channel was as follows:
  Corrected hull temperature = raw hull temperature -0.031.

  Quality control report

  Data quality is generally very good. On two occasions (18/07/2004 05:19-18:52 and 25/07/2004 07:45-21:18) there is a significant drop in temperature, each by approximately 3 °C.

• Salinity

  Standard seawater routines were used to derive salinity from the conductivity and corrected housing temperature channels. Back calibration of salinity was subsequently achieved with 31 independent salinity values, using a combination of discrete TSG samples and concurrent CTD surface salinity values, averaged over the top 5 m. The independent salinity values from the CTD were obtained from the primary CTD salinity channel. There was no significant difference between data from the primary or secondary salinity channels. The TSG and CTD values used for calibration will be referred to in the text as calibration samples.

  Examination of the offset (calibration samples - underway salinity) against time revealed two distinct clusters of data. Various attempts at calibration were carried out, including regression analysis, but the best fit was to apply two mean offsets to the cruise: one for the period up to midday 13/07/2004 and one after this time. Midday on 13/07/2004 was chosen arbitrarily, since it is approximately mid way between the time of the last calibration sample in the first period and the first sample in the second period. The calibration residuals of the overall dataset range between -0.1746 and 0.1846, the root mean square of the residuals is 0.085.

  The correction applied to the salinity channel was as follows:
  Calibrated salinity 01/07/2005 to 12:00 13/07/2005 = uncalibrated salinity -1.422.
  Calibrated salinty 12:01 13/07/2005 to end of cruise = uncalibrated salinity -2.027.

  Quality control report

  Applying two offset corrections caused a significant step in the time series at 12:00 on 13/07/2005. Data were flagged suspect from midnight on 12/07/2005 until midnight on 13/07/2005 to account for changeover in calibration offsets.

• Beam attenuation

  Raw voltages were converted to beam attenuation after correction with air readings obtained during cruise CD160, which took place immediately following CD159. The equation used was:

  Attenuation = -1/PL*ln((Va/Vb)*k*20*(Vx-Vz)/100)

  where PL = path length = 0.2 m; Va = transmission voltage in air (recorded by the manufacturer at water calibration time) = 4.684; Vb = transmission voltage in air (current value) = 4.405; k = water calibration constant = 1.002; Vx = transmissometer output voltage; Vz = blocked path voltage = 0.001.

  Quality control report

  The underway beam attenuation signal has two distinct large steps present, where the signal ramps up over a period of time and then suddenly drops to a lower level. This was investigated by comparing CTD beam attenuation in the top 5 m with the underway record over the cruise period. It was noted that the ramping up periods coincided with poor agreement between the CTD and underway measurements.

  It is therefore evident that the underway transmissometer was not returning reliable data for significant periods of time. Using the CTD intercomparison as a guide, the following periods have been flagged suspect:

  • start of cruise until 04/07/2004
  • 17:25 11/07/2004 until 12:00 16/07/2004

  There are remaining periods where the data are noisy, which have also been flagged, but there is reasonably good agreement between the remaining transmissometer data and the fluorometer . One noticeable exception to this occurs between 13:52 (07/07/2004) and 04:11 (08/07/2004) where a steep increase in beam attenuation is only initially mirrored by an increase in the fluorometer output voltage (until 15:20 on 07/07/2004), after which the values decrease significantly. The elevated data values in both channels during this period are considered suspect, and have been flagged accordingly.

• Fluorescence

  Fluorescence data were logged as raw voltages, and it was not possible to process the data any further.

  Quality control report

  The data in this channel are relatively clean. There is a step in the data occurring between 07:41 and 11:20 on 16/07/2004, with a voltage decrease of approximately 5 volts.

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.

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: