Metadata Report for BODC Series Reference Number 610117

• 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

Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

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.

Kipp and Zonen Pyranometer Model CM6B

The CM6B pyranometer is intended for routine global solar radiation measurement research on a level surface. The CM6B features a sixty-four thermocouple junction (series connected) sensing element. The sensing element is coated with a highly stable carbon based non-organic coating, which delivers excellent spectral absorption and long term stability characteristics. The sensing element is housed under two concentric fitting Schott K5 glass domes.

Specifications

Vaisala Analog Barometers Models PTB100 (A), (B) and PTB101 (B), (C)

The PTB 100 series analog barometers are designed both for accurate barometric measurements at room temperature and for general environmental pressure monitoring over a wide temperature range. The long-term stability of the barometer minimizes the need for field adjustment in many applications.

Physical Specifications

The barometers use the BAROCAP^* silicon capacitive absolute pressure sensor developed by Vaisala for barometric pressure measurements. The BAROCAP^* sensor combines the elasticity characteristics and mechanical stability of a single-crystal silicon with the proven capacitive detection principle.

Sensor Specifications

^* BAROCAP is a registered trademark of Vaisala

Vaisala WA15 Wind Set

The WAA151 combines a WAA151 anemometer and a WAV151 wind vane, to measure wind speed and direction.

WAA151 Anemometer

The anemometer has three lightweight conical cups in the cup wheel. A wind-rotated chopper disc, attached to the cup wheel's shaft, cuts an infrared light beam 14 times per revolution, generating a pulse output from a phototransistor. The output rate can be regarded as directly proportional to the wind speed. However, for the best accuracy, a transfer function is used to compensate starting inertia and slight over-speeding:

U_f = 0.328 + 0.101 x R, where U_f = wind speed and R = output pulse rate

A thermostatically controlled heating element in the shaft tunnel prevents the bearings from freezing in cold environments.

WAV151 Wind Vane

The WAV151 is a counter-balanced optelectronic wind vane. Infrared LEDs and phototransistors are mounted in six orbits around a 6 bit Gray coded disc. Turned by the vane, the disc determines the code received by the phototransistors.

Specifications

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

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.

Didcot Cosine Photosynthetically Available Radiation (PAR) sensors

The silicon cell, blue glass filter and diffuser are bond together using optically clear adhesive, the complete assembly is mounted into the black anodised body and sealed using the same adhesive. The body has a raised rim to provide to provide low angle cosine correction and holes within the rim to provide drainage for surface water which would otherwise affect the instrument's accuracy. Model DRP-5 has an integral clamp to mount on a vertical mast tube, model DRP-5B has round base with three leveling screws and is intended to stand on a flat surface and model DRP-4 has a built in integrator to record total PAR received over a period of time.

Technical Information

Falmouth Scientific Instruments (FSI) Thermosalinograph

FSI's Excell^* Thermosalinograph uses FSI's patented internal field conductivity sensor (NXIC cell) and two precision platinum thermometers to provide salinity. Dual temperature sensors are used at the inlet and outlet of the thermosalinograph to assure an integrated temperature across the conductivity sensor. The system is cast in a urethane mold and the electronics are housed in an integral sealed (moisture-proof) housing. Flow through the system is via 3/4" hose pipe barbs.

Features

• Salinity Range 2 to 42 PSU
• Salinity Accuracy to ± 0.030 PSU
• Patented NXIC Internal-Field Inductive Conductivity Sensor
• Standards-Grade Platinum Resistance Thermometers
• Internal Reference and Self-Calibrating Electronics
• Standard Digital Output for Direct Computer Connection

^*Copyright 2001, Falmouth Scientific, Inc. All rights reserved.

RRS Discovery DI234/98 Underway Instrumentation

Navigation

• Global Position system (GPS)
• Ship's gyro
• Electro Magnetic (EM) log

Meteorology

• Port and starboard solar radiation meters
• Port and starboard PAR irradiance sensors
• Temperature and Humidity sensor
• Conventional cup and vane anemometer
• Analog Barometer

Physics

• Thermosalinograph
• Transmissometer

Biology

• Fluorometer

Data Acquisition

Data logging and initial processing was handled by the RVS ABC system. The Level A sampling microcomputer digitises an input voltage, applies a time stamp and transfers the data via the Level B disk buffer onto the Level C where the data records are assembled into files. Sampling rates vary from 10 seconds to 30 seconds.

The level C included a suite of calibration software which was used to apply initial calibrations to convert raw ADC counts into engineering units. At the end of the cruise, the Level C disk base was transferred to BODC for further processing.

BODC Underway Data Processing Procedures

All underway data files are merged into a common file using time (GMT) as the primary linking key. Data logged as voltages (e.g. PAR irradiance, fluorometer and transmissometer) are converted to engineering units, wind velocity is corrected for ship's motion and heading and any additional calibrations are applied as appropriate. These are discussed in the individual instrument documentation.

Each data channel is visually inspected on a graphics workstation and any spikes or periods of dubious data are flagged as suspect. The capabilities of workstation screening software allows all possible comparative screening checks between channels (e.g. to ensure corrected wind velocity 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.

Chlorophyll Processing Notes

Chlorophyll fluorescence was measured by a WetStar fluorometer (Serial No. 117). The data were logged as voltages every 30 seconds and reduced by averaging to 1-minute values at BODC. The data were examined graphically and any suspect data flagged.

A data set of 205 fluorometrically assayed extracted chlorophyll samples analysed onboard by the University of East Anglia were made available for the fluorometer calibration. The extracted values range from 0.33 to 2.53 mg m^-3. Residuals from an initial calibration between extracted samples and fluorometer output were significantly correlated with PAR.

The calibration gave the equation (n= 198, R²= 0.748):

• chlorophyll = exp(1.198 (±0.05)* ln(raw_fluor) +0.0034 (±0.0002) * PAR - 7.074 (±0.3)

Meteorology - Air Temperature and Humidity Processing Notes

The Metpac fitted on Discovery for this cruise included a Vaisala temperature and humidity sensor HMP44L (Serial No. S5040001) calibrated by the manufacturer on 11/12/1997 and mounted centrally on the platform. Output was generated in engineering units (°C and %) and logged every 5 seconds. The data were later reduced to 1 minute sampling by averaging at BODC. The data were inspected on a graphics workstation and no problems were detected other than occasional spike and a small number of stack pollution events. These have been flagged suspect.

During the cruise, the air temperature data were regularly checked against measurements from the bridge sensors and were found to be in good agreement.

Meteorology - Barometric Pressure Processing Notes

Barometric pressure was measured by a PTB100A Vaisala analog barometer (Serial No. R0450005), calibrated by the manufacturer on 26/01/1996. The instrument outputs data in millibars which were logged every 5 seconds. The data were later reduced to 1 minute sampling by averaging at BODC and visually inspected on a graphics workstation, any spikes were flagged suspect. The record was good, although a number of sudden drops to zero were observed and flagged suspect.

No correction has been applied for the height of the instrument above sea level.

During the cruise, the data were checked against the meteorological logs maintained by the deck officers. These showed that the Vaisala was found to be reading consistently 2-3 mbar lower than the bridge instrument. However, the bridge data were corrected to sea level which accounts for most of the difference.

Meteorology - Photosynthetically Available Radiation (PAR) Processing Notes

The scientific meteorological package on Discovery is mounted on a large platform running some 8 m from port to starboard at the junction of the two main stanchions of the foremast. This is approximately 15.5 metres above sea level.

Didcot cosine collector PAR sensors (spectral range 400-700 nm) calibrated in July 1997 were mounted on the port and starboard side of the meteorology platform (DRP-1G Serial No. 0151 on starboard and DRP-1G1M Serial No. 1678 on port). The sensors were logged every 30 seconds but were later reduced to 1 minute sampling by averaging.

The port and starboard data were visually inspected on a graphics workstation, any spikes were flagged as suspect. A merged PAR irradiance channel was then produced by taking the maximum of the port and starboard values to eliminate shading effects. The merged data were visually re-inspected.

Quality control report

The visual inspected suggested there to be a problem with these data. It was noticed that dubious data points in the PAR irradiance channel were echoed in solar radiation, relative wind speed and relative wind direction data channels. Since all dubious values were equivalent to approximately half of the expected value, it was realised that null values associated with instrument malfunction or missing data had not been recognised as absent data by the averaging software and had been used in the calculation of the 1-minute average record. Subsequently, all dubious data resulting from null values being included in the averaged data set have been flagged as suspect.

Meteorology - Total Solar Radiation Processing Notes

The scientific meteorological package on Discovery is mounted on a large platform running some 8 m from port to starboard at the junction of the two main stanchions of the foremast. This is approximately 15.5 metres above sea level.

Kipp and Zonen pyranometers CM6B (maximum spectral range 305-2800 nm) calibrated by the manufacturer in January 1996 were mounted on the port and starboard side of the meteorology platform (Serial No. 962276 to the port and Serial No. 962301 to the starboard). The sensors were logged every 30 seconds and were later reduced by averaging.

The port and starboard data were visually inspected on a graphics workstation, any spikes were flagged as suspect. A merged solar radiation channel was then produced by taking the maximum of the port and starboard values to eliminate shading effects. The merged data were visually re-inspected.

Quality control report

The visual inspected suggested there to be a problem with these data. It was noticed that dubious data points in the solar radiation channel were echoed in PAR irradiance, relative wind speed and relative wind direction data channels. Since all dubious values were equivalent to approximately half of the expected value, it was realised that null values associated with instrument malfunction or missing data had not been recognised as absent data by the averaging software and had been used in the calculation of the 1-minute average record. Subsequently, all dubious data resulting from null values being included in the averaged data set have been flagged as suspect.

Meteorology - Wind Velocity Processing Notes

A Vaisala cup and vane anemometer WAA151 was mounted on the meteorological platform. The Vaisala vane was mounted with zero to port.

The instrument generated relative wind speed in m/s and relative wind direction in degrees. These were logged every 5 seconds but were later reduced by BODC to 1 minute sampling by averaging wind speed and taking spot wind direction values every minute from the 5 second stream. Spot values of ship's heading taken every minute and averaged ship's velocity over the ground (from data logged every 30 seconds) were also available. All these data channels were examined on a graphics workstation and any suspect values flagged.

The visual inspected suggested there to be a problem with these data. It was noticed that dubious data points in the relative wind speed and relative wind direction data channels were echoed in solar radiation and PAR irradiance channels. Since all dubious values were equivalent to approximately half of the expected value, it was realised that null values associated with instrument malfunction or missing data had not been recognised as absent data by the averaging software and had been used in the calculation of the 1-minute average record. Subsequently, all dubious data resulting from null values being included in the averaged data set have been flagged as suspect.

The ship's heading was added to the relative wind direction and 90 degrees subtracted to correct for the vane orientation. The resulting value was constrained to the range 0-359 by adding or subtracting 360 as appropriate. The ship's velocity over the ground was then subtracted from the relative wind velocity to give the absolute wind velocity. Note that as the two velocities have opposite sign conventions, this is effectively an addition of the velocities converted to uniform sign convention.

The data were re-screened on a workstation. Comparative screening checks were made to ensure that the absolute wind velocity was truly independent of the ship's velocity and heading. This proved to be the case except for spikes (usually in absolute direction but occasionally in speed as well) coinciding with times when the ship was accelerating or decelerating. These have been attributed to the mismatch in the sampling rates of the navigation and meteorology and have been flagged suspect. The proportion of the data set affected is less than 0.1 per cent.

No attempt has been made to correct the data to a standard height of 10m.

Regular checks of the absolute wind velocity were made against the 6 hourly meteorological logs maintained by the deck officers. Approximately 80% of the wind speeds agreed to within 5 knots and about 70% of the wind directions agreed to within 25 degrees. Major differences in wind direction occurred at low wind speed and were probably due to the wind swirling. The anemometer was noted to be slow to respond to changes in wind direction.

Optical Attenuance Processing Notes

Optical attenuance was measured using a SeaTech 660 nm (red) 20cm path length transmissometer (Serial No. T1005). The instrument windows were cleaned once a week during the cruise.

The data were logged as voltages every 30 seconds. The data frequency was then reduced to 1 minute by averaging. The data were corrected for light source decay by multiplying the voltages by a factor of 1.0189 based on an air reading after careful cleaning of the instrument optics.

Voltages were converted to percentage transmission by multiplying by 20. Any values outside the operational limits of the instrument (1-91.3%) were automatically flagged suspect.

The percentage transmission was converted to attenuance using the equation:

• Attenuance = -4.0 log (% Transmission/100)

Position Processing notes

Global Positioning System (GPS) was the primary navigation system used. When GPS fixes were unavailable the ship's position was determined by dead reckoning based upon the ship's gyro and EM log. Once a fix was obtained the surface drift velocity was computed. If this exceeded four knots the data were automatically flagged suspect, else a correction for the positional error due to surface drift was retrospectively applied over the period of dead reckoning.

Null values in the latitude and longitude channels were also identified and checked to ensure that the ship's speed over the ground did not exceed 15 knots.

Thermosalinograph Processing Notes

Temperature and salinity were measured using a Falmouth Scientific Instruments Thermosalinograph, incorporating a remote temperature sensor (thermolinear thermistor Serial No. 1340, calibrated - 21 Jan 1998) and an inductive-type conductivity cell (Serial No. 1341) mounted next to a second thermistor (Serial No. 1339, calibrated - 22 Jan 1998).

The raw ADC counts were calibrated to give conductivity and two temperature channels based upon laboratory calibrations undertaken by RVS. Salinity was computed from the housing temperature and conductivity using the UNESCO 1978 Practical Salinity Scale (Fofonoff and Millard, 1982).

The data were sampled every 30 seconds and were reduced to a 1 minute data stream by averaging at BODC. The averaged temperature and salinity streams were inspected on a graphics workstation and all suspect values flagged.

Salinity was back calibrated using a set of 122 discrete salinity measurements on samples taken from the thermosalinograph outlet. Samples were collected in glass bottles to just below the neck and sealed with plastic stoppers. Batches of samples were left for at least 24 hours to reach thermal equilibrium. Samples were analysed on a Guildline Autosal bench salinometer. Analysis of the difference between thermosalinograph and bottle salinities revealed that the instrument drifted linearly with time throughout the cruise. The correction applied to the data was as follows:

• Corrected salinity = Raw salinity + (Cycle_number*1.305913 10-6) + 0.17204

The residuals (bottle salinity - thermosalinograph salinity) after calibration averaged -0.002 ±0.011 PSU (range: -0.027 to +0.027, N=122) for bottle salinity ranging between 35.206 and 35.332 PSU. Comparison with surface CTD salinity gave an averaged difference (CTD salinity - thermosalinograph salinity) of 0.005 ±0.012 (range: -0.028 to +0.026, N=54) for CTD salinity ranging between 35.218 and 35.407.

The remote (i.e. sea surface) temperature was back calibrated against readings from the calibrated CTD temperature averaged over the upper 5 m depth. A total of 54 paired samples showed a significant consistent offset between the thermosalinograph and the CTD temperature with no evidence of temporal drift or relationship with temperature. The correction applied to the temperature channel was as follows:

• Corrected temperature = raw_temperature - 0.024

With the exclusion of CTD data points with STD<0.01°C in the upper 5 m and underway records with STD< 0.01°C over the duration of the cast, residuals (CTD temperature - thermosalinograph temperature) after calibration averaged 0.000 ±0.010 PSU (range: -0.021 to +0.028, N=35).

The thermosalinograph generally worked well during the cruise. There are periods of temperature noise which corresponded to clear sunny days with a sea state of zero or one and are believed to be related to the formation of uneven shallow thermoclines. As they are the result of real phenomena, no attempt has been made to flag or otherwise reduce the noise.

Project Information

ACSOE Marine Aerosol and Gas Exchange (MAGE)

Marine Aerosol and Gas Exchange (MAGE) was a component of the NERC Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) project aimed at studying chemical exchange across the air-sea interface.

The component included two experiments that were purely a part of ACSOE:

• Eastern Atlantic Experiment (spring 1996 and 1997)
• North Atlantic Experiment (June 1998)

In addition, MAGE contributed ship time in October 1996 to the EU ASGAMAGE project and this was included as an experiment within the organisational structure of MAGE.

Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE)

Introduction

ACSOE was a NERC Thematic Research Programme which investigated the chemistry of the lower atmosphere (0-12 km) over the oceans. The studies aimed to bring about a clearer understanding of natural processes in the remote marine atmosphere, and how these processes are affected by atmospheric pollution originating from the continents. This information is vital to help understand regional and global-scale changes in atmospheric chemistry and climate.

Aims and Objectives

The £3.9 million NERC-funded programme was instigated as a major UK contribution to this international scientific effort between 1995 and 2000. The overarching aim of ACSOE was to investigate the processes that control the production and fate of trace gases and particles (condensation nuclei and aerosols) in the atmosphere over the oceans. For convenience it was divided into three separate but linked activities:

1. MAGE, Marine Aerosol and Gas Exchange - to study air-sea exchange especially of atmospherically-important gases produced by marine microorganisms, such as dimethyl sulphide (DMS) and carbon dioxide (CO2)
2. OXICOA, Oxidising Capacity of the Ocean Atmosphere - a study of the tropospheric ozone budget and underlying chemistry
3. ACE, Aerosol Characterisation Experiment - to investigate the development of aerosols and clouds in European air spreading out into the Atlantic Ocean

The project had several objectives including:

• To determine the ozone budget of the background lower atmosphere (i.e. the troposphere)
• To study the sunlight-initiated chemistry of gases and particles (aerosol) in the background atmosphere
• To determine the importance of night-time chemistry
• To seek evidence for extensive halogen atom chemistry
• To measure air-sea gas transfer rates
• To assess the role of coastal and open ocean waters as sources of reactive gases
• To observe the effects of atmospheric deposition on oceanic biogeochemistry
• To investigate how clouds are affected by the chemistry of the inflowing air
• To identify within-cloud processes affecting particle size and chemistry

Project Co-ordination:

The programme was led by Professor Stuart Penkett of the University of East Anglia and involved over 100 scientists from leading British and International universities and institutes. Atmospheric data are held at BADC and data collected in the marine environment for the MAGE component of the programme are held at BODC.

Fieldwork description:

Fieldwork was carried out in 1996, 1997 and 1998 and involved air-, land- and sea-based measurements, coupled with modelling studies. Measurements were made at remote field sites (Mace Head, Ireland; Weybourne, Norfolk; Tenerife), from the NERC research vessels Challenger and Discovery and aboard the Meteorological Research Flight C-130 and the Cranfield Jetstream aircraft.

ACSOE North Atlantic Experiment (NAE)

The North Atlantic Experiment was a pert of the Marine Aerosol and Gas Exchange (MAGE) component of the Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) project.

The aims of the experiment were:

• To investigate the mechanisms producing climatically important gases in seawater
• To investigate how the rates of climatically important gas production vary with biological and physiochemical parameters
• To assess whether measured gaseous emissions can be used in models to identify the major atmospheric transformation processes
• To investigate how the plankton community responds to atmospheric deposition of nutrients in terms of growth rates and production of climatically important trace gases and their precursors

The experiment was based around an RRS Discovery cruise in June and early July 1998 that followed the development of a bloom in a patch of water marked with SF₆. Associated aircraft overflights to investigate the physical and chemical evolution of particles in the marine boundary layer were planned but were not possible.

A wide range of oceanographic, meteorological and atmospheric parameters were measured during the cruise. The fieldwork was supported by modelling work with a zero-dimensional time-dependent photochemical box model of an air mass in the marine boundary layer.

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: