Metadata Report for BODC Series Reference Number 1359918

• 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

RRS Discovery AMT16 (D294) - Continuous Underway Hydrographic Data Quality Report

The quality of the fluorometer and transmissometer records was affected by the blockage in the flow loop containing these sensors for 14 days in the middle of the cruise (30th May to 13th June, 2005). These periods were flagged as suspect for both instruments during screening.

Although there were extracted chlorophyll data from samples taken from the non-toxic supply, the decision was taken not to apply calibrations to the highly variable fluorometer data at either end of the cruise track; instead the extracted chlorophyll dataset should be used for surface chlorophyll data along the cruise track.

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.

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.

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.

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.

RRS Discovery AMT16 (D294) - Continuous Underway Hydrographic Instrumentation Document

RRS Discovery AMT16 (D294) - Continuous Underway Hydrographic Processing Document

Originator's Data Processing

SurfMet, the UKORS surface water and meteorological suite of instrumentation was run for the duration of the cruise. The SurfMet system was controlled via a LabView program running on a desktop PC and logged the data at 30 second intervals to the ship's central data logging (ABC) System in the RVS format file 'surftmp'. The system was inadvertently stopped from logging mid-cruise resulting in a loss of around 4 hours of data. The temperature and conductivity data were used to calculate the surface salinity and were logged in the RVS file 'protsg'.

The transmissometer and fluorometer flow loop was stopped occasionally to clean the transmissometer lenses and take air and blank readings. After one cleaning event this loop appears to have stalled, even though the flow meter indicated flow. Hence there is bad data logged by the transmissometer and fluorometer between Julian Days 150 and 164 (30th May to 13th June, 2005).

BODC Data Processing

Reformatting

Data from the full-resolution RVS files were transferred to BODC's NetCDF format (QXF) under the BODC Underway Data System (BUDS). This transfer involved reducing the data to 30 second intervals using averaging. Directional data were reduced by averaging using a unit circle.

Screening

Each data channel was inspected on a graphics workstation and any spikes or periods of dubious data were flagged. The power of the workstation software was used to carry out comparative screening checks between channels by overlaying data channels. A map of the cruise track was simultaneously displayed in order to take account of the oceanographic context.

Data processing, correction and calibration

The data were loaded from the RVS files 'protsg' and 'surftmp'.

The raw voltage channels for the fluorometer and transmissometer were transferred and converted from mV to V (conversion factor = x0.001). Data were flagged for periods where the non-toxic supply was turned off and for spikes associated with cleaning operations.

Salinity

Salinity data from the thermosalinograph have been compared with calibrated surface CTD data to a depth of 7 db and samples collected from the underway system and analysed with a bench salinometer. The analysis showed that there was a drift in the salinity measurement with time during the cruise. This was corrected using a linear offset against time.

The root mean square (RMS) error for the calibration dataset (n = 102) was calculated between the bench salinometer data and both the uncalibrated TSG and calibrated salinity.

The decrease in the RMS error indicates the calibration improves the match between the CTD and sample salinities and the TSG sensor. Once the calibration was applied the average offset was-9.3x10^-5, with SD 0.009.

Temperature

Hull mounted temperature sensor data was checked against the CTD temperature measurements averaged over the upper 7 db of the water column. Only CTD data points and underway records with a standard deviation lower than 0.01 °C were considered. The offset was calculated from CTD temp - hull sensor temp, which was then plotted against both time and CTD temperature. There was a significant regression with the offset against both time and CTD temp. Since the regression against time explained a greater proportion of the variance a linear offset was determined against cruise time and values determined for the start and end of the cruise. The BODC calibration system then generated the offset to be added for each time interval in between.

The root mean square (RMS) error for the calibration dataset (n = 46) was calculated between the CTD sensor temperature and both the uncalibrated and calibrated hull sensor temperature.

The decrease in the RMS error indicates the calibration improves the match between the CTD temperature and the hull temperature sensor. Once the calibration was applied the average offset was-2.2x10^-5 °C, with SD 0.014 oC.

Chlorophyll

Calibration of the fluorometer channel was attempted by comparing the raw fluorometer output voltage with chlorophyll concentration values extracted from samples collected from the ship's non-toxic water supply (n = 138). However the loss of 14 days fluorometer data reduced the calibration samples (n = 86) and reduced coverage during the middle of the cruise. Therefore the fluorometer data have not been calibrated and BODC recommends the use of the underway sampled extracted chlorophyll dataset, which provides good coverage along the cruise track.

Transmissometer

There was no record available of the transmissometer serial number and so no calibration sheet can be supplied for this instrument. Despite air and dark readings being taken during the cruise a calibration cannot be reliably applied and the data therefore remain as a voltage.

Project Information

The Atlantic Meridional Transect - Phase 2 (2002-2006)

Who was involved in the project?

The Atlantic Meridional Transect Phase 2 was designed by and implemented by a number of UK research centres and universities. The programme was hosted by Plymouth Marine Laboratory in collaboration with the National Oceanography Centre, Southampton. The universities involved were:

• University of Liverpool
• University of Newcastle
• University of Plymouth
• University of Southampton
• University of East Anglia

What was the project about?

AMT began in 1995, with scientific aims to assess mesoscale to basin scale phytoplankton processes, the functional interpretation of bio-optical signatures and the seasonal, regional and latitudinal variations in mesozooplankton dynamics. In 2002, when the programme restarted, the scientific aims were broadened to address a suite of cross-disciplinary questions concerning ocean plankton ecology and biogeochemistry and the links to atmospheric processes.

The objectives included the determination of:

• how the structure, functional properties and trophic status of the major planktonic ecosystems vary in space and time
• how physical processes control the rates of nutrient supply to the planktonic ecosystem
• how atmosphere-ocean exchange and photo-degradation influence the formation and fate of organic matter

The data were collected with the aim of being distributed for use in the development of models to describe the interactions between the global climate system and ocean biogeochemistry.

When was the project active?

The second phase of funding allowed the project to continue for the period 2002 to 2006 and consisted of six research cruises. The first phase of the AMT programme ran from 1995 to 2000.

Brief summary of the project fieldwork/data

The fieldwork on the first three cruises was carried out along transects from the UK to the Falkland Islands in September and from the Falkland Islands to the UK in April. The last three cruises followed a cruise track between the UK and South Africa, only deviating from the traditional transect in the southern hemisphere. During this phase the research cruises sampled further into the centre of the North and South Atlantic Ocean and also along the north-west coast of Africa where upwelled nutrient rich water is known to provide a significant source of climatically important gases.

Who funded the project?

Natural Environment Research Council (NERC)

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: