Metadata Report for BODC Series Reference Number 610105
No Problem Report Found in the Database
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."
The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.
The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.
Further details can be found in the manufacturer's specification sheet.
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.
|Chlorophyll WETStar||CDOM WETStar||Uranine WETStar||Rhodamine WETStar||Phycoerythrin WETStar|
|Excitation wavelength||460 nm||370 nm||485 nm||470 nm||525 nm|
|Emission wavelength||695 nm||460 nm||530 nm||590 nm||575 nm|
|Sensitivity||0.03 µg l-1||0.100 ppb QSD||1 µg l-1||-||-|
|Range||0.03-75 µg l-1||0-100 ppb; 0-250 ppb||0-4000 µg l-1||-||-|
|Depth rating||600 m|
|Response time||0.17 s analogue; 0.125 s digital|
|Output||0-5 VDC analogue; 0-4095 counts digital|
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.
|Dimensions (W x H)||150.0 mm x 91.5 mm|
|Operating Temperature||-40°C to +80°C|
|Spectral Range||305 - 2800 nm |
|Sensitivity||9 -15 µV/W/m2|
|Impedance (nominal)||70 - 100 ohm|
|Response Time (95%)||30 sec|
|Non-linearity||< ± 1.2% (<1000 W/m2)|
|Temperature dependence of sensitivity||< ± 2% (-10 to +40°C)|
|Zero-offset due to temperature changes||< ± 4 W/m2 at 5 K/h temperature change|
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.
- 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)
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 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.
- 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 Challenger CH133/97 Underway Instrumentation
- Global Positioning System (GPS)
- Ship's gyro
- Electro Magnetic (EM) log
- Echo Sounder
- Port and starboard solar radiation meters
- Port and starboard 2-pi PAR irradiance sensors
- Port and starboard PAR irradiance sensors
- Temperature and Humidity sensor
- Conventional cup and vane anemometer
- Aneroid barometer
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 several minutes.
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.
Bathymetry Processing notes
A SimRad EA500 deep echo sounder was operated throughout the cruise using a hull transducer. The data were sampled at 30 seconds intervals and were corrected for the sensor depth below sea surface (4 m) and for variation of sound velocity in sea water (Carter's Tables Corrections). The data were reduced to 1 minute sampling by averaging at BODC. The resulting channel was visually examined on a graphics workstation and suspect values were flagged.
Chlorophyll Processing Notes
A Chelsea Instruments Aquatracka fluorometer was mounted in a closed plastic tank on the starboard deck, continuously fed with sea water from the non-toxic supply. A WetStar linear response miniature fluorometer was included in the flow-through housing in the ship's fish laboratory.
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 fluorometrically assayed extracted chlorophyll samples analysed at the University of East Anglia were made available for fluorometer calibration. These were taken approximately hourly whenever the ship was underway. BODC have some concerns about these data. The phaeopigment values supplied were mainly negative and the data set was interspersed with high values which were not accompanied by a noticeable reaction from either fluorometer. Twenty of the 212 values supplied were excluded from the calibration and flagged suspect in the database. These encompassed virtually all the values in the extracted data set in excess of 2.5 mg/m 3 . In spite of this data set reduction the regression statistics of both fluorometer calibrations are extremely poor.
The Aquatracka calibration gave the equation:
- chlorophyll = exp (0.8*Volts - 0.3435) (R 2 =20%)
The WetStar calibration gave the equation:
- chlorophyll = Volts*0.4443 - 0.1619) (R 2 =33%)
Comparison of the two calibrated fluorometer channels showed surprisingly good agreement except for the later stages of the cruise when the WetStar read significantly lower than the Aquatracka. Nevertheless, in view of the extremely poor calibration statistics these data should be considered semi-quantitative at best.
Meteorology - Air temperature and Humidity Processing Notes
A Vaisala temperature and humidity sensor was mounted centrally on the foremast. The data were logged in engineering units (°C and %) every 5 seconds and were later averaged to 1 minute intervals at BODC. The data were visually inspected on a graphics workstation. 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 checked against measurements logged by the deck officers using independent instruments mounted in a Stevenson screen on the Monkey Island. This showed the Vaisala to be reading on average 0.126°C higher (standard deviation 0.31°C). No correction for this has been applied.
Please note that the Vaisala humidity sensor is a low grade instrument, with possible accuracy limitations, as readings (not spikes) of over 100% reveal .
Meteorology - Barometric Pressure Processing Notes
A Vaisala aneroid barometer was mounted on the central platform of the foremast. The instrument output data in millibars which was logged every 5 seconds. These data were reduced by averaging to 1 minute sampling at BODC and visually examined on a graphics workstation. Any spikes were 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 reading 2.29 mbar lower on average (standard deviation 0.35 mbar) than the bridge instrument. However, the bridge data were corrected to sea level which accounts for 1.9 mbar of this difference.
Meteorology - Photosynthetically Available Radiation (PAR) Processing
PML designed 2-pi PAR irradiance meters were mounted in pairs in gimballed housings on the port and starboard side of the 'Monkey Island' above the scientific plot. The starboard location is far from ideal due to a large satellite communication radome which frequently shaded the instrument. The instruments were clean daily during the cruise.
The sensors were logged as voltages every 30 seconds and later averaged to 1 minute values and calibrated in W m-2 by BODC using coefficients determined in July 1995. The calibration equations used were:
|PAR = exp(Volts*4.97 + 6.526)/100|
|PAR = exp(Volts*4.91 + 6.952)/100|
A merged PAR channel was produced, after spikes were flagged out, by taking the maximum of the port and starboard values to eliminate shading effects.
It has been determined by empirical calibration that the PAR values in W m-2 measured by the PML 2-pi PAR sensors may be converted to µE/m2/s by multiplying by 3.75.
It must be emphasised that these instruments have hemispherical domed collectors, considerably enhancing their light collection efficiency, particularly when the sun is lower in the sky. Consequently, simple comparisons between data from these instruments and other equipment with differing geometry must not be attempted.
Meteorology - Photosynthetically Available Radiation (PAR) Processing
Two planar PAR radiance sensors were mounted on the meteorological package platform on the port and starboard sides of the foremast. The sensors were logged every 5 seconds as a voltage and were converted to W m-2 from volts using the manufacturer's calibrations.
The data were reduced to 1 minute sampling at BODC by averaging and any spikes found in the port and starboard channels were flagged suspect. A merged PAR channel was then produced by taking the maximum of the port and starboard values to eliminate shading effects.
Meteorology - Total Solar Radiation Processing
Kipp and Zonen solar radiation meters were mounted in gimballed housings on the port and starboard side of the 'Monkey Island' above the scientific plot. The starboard location is far from ideal due to a large satellite communication radome which frequently shades the instrument. The instruments were cleaned daily during the cruise.
The instruments were connected to a data integrator which converted the instrument voltages into Wm-2 and integrated the values producing 10 minute and running total integrations in kJ m-2. The output from the integrator was logged at the end of each integration period.
At BODC, the 10 minute integrations were merged into the underway file by a custom program that divides the integrated energy by the integration interval to give an averaged irradiance value. The time stamp is also adjusted to the mid-point of the averaging interval by subtracting 5 minutes.
A visual observation of the data revealed an obvious problem. The values were much too small, with a maximum value of 250 W m-2 recorded during the cruise, whereas a value of nearer 1000 W m-2 would be expected. This problem has been observed by BODC before. It suddenly appeared at the start of cruise Challenger CH128 after the system had functioned perfectly well during the previous cruise. Communications with RVS on the subject have failed to produce either an explanation or a cure. The integrator is the prime suspect as a cause and the most likely explanation is that the integration period has changed.
When compared to the other radiometer data, the instruments are obviously functioning perfectly. It's just the absolute values that are wrong by a factor of 4. Rather than jettison the data, an empirical 'correction' has been applied: i.e. all the data have been multiplied by 4. There is no scientific basis for this other than all the hallmarks of the problem are that the data have been scaled and that multiplying by 4 give midday values on clear sunny days (such as May 31st) that are within 5% of data observed at the same time of year and at the same latitude with the system functioning normally.
A merged solar radiation channel was produced, after spikes were flagged out, by taking the maximum of the port and starboard values to eliminate shading effects.
Meteorology - Wind Velocity Processing Notes
A Vaisala cup and vane anemometer was mounted on the meteorological package platform on the foremast (approximately 12 m above sea level) with the cup to port and the vane to starboard. The Vaisala vane was mounted with zero to starboard.
The instrument was sampled every 5 seconds and generated relative wind speed in m/s and relative wind direction in degrees. The wind speed was converted to knots by multiplying by 1.94. At BODC the wind speed was reduced to 1 minute sampling by averaging and spot wind direction values were taken every minute from the 5 second stream. The merged file also included spot values of ship's heading taken every minute and averaged ship's velocity over the ground (from data logged every 30 seconds). All these data channels were examined on a graphics workstation and any suspect values flagged.
The ship's heading was added to the relative wind direction and 270 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 then 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.
During the cruise, regular checks of the wind velocity was made against the meteorological logs maintained by the deck officers. On average the wind speeds were within 1.5 knots (standard deviation 3.2 knots) and the wind directions were within 6 degrees (standard deviation 25 degrees).
Optical Attenuance Processing Notes
Optical attenuance was measured using a SeaTech 660 nm (red) 25cm path length transmissometer contained in a plastic water bath continuously flushed by the non-toxic supply. The instrument windows were cleaned regularly and the tank was occasionally washed out with Decon90 to prevent the development of marine fouling.
The data were logged as voltages every 30 seconds but were later reduced to 1 minute by averaging at BODC. 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).
Inspection of the data using a graphics workstation showed the optical attenuance data to be of unusually poor quality. Heavy flagging was required at times due to the presence of characteristic 'bubble spikes'. In addition, there were significant periods when the transmissometer was giving anomalously high readings for no apparent reason although the possibility of 'semi-permanent' bubbles due to air in the non-toxic supply cannot be ruled out . These have been flagged as suspect.
A second transmissometer (a C-star model 9603014) was fitted to the new flow-through system in the ship's fish laboratory. This instrument produced an equally noisy data set, giving credence to bubbles being the cause of the problem. In addition the data when calibrated in terms of attenuance appeared anomalously high. Consequently, they have not been included in the final data set.
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) and an inductive-type conductivity cell mounted next to a second thermistor.
The ship is fitted with a non-toxic pumped sea water supply with water drawn from an inlet approximately 4 m below the surface. The thermosalinograph was fed from the non-toxic supply via a small header tank to remove bubbles. Tests on previous Challenger cruises have shown that the residence time from the inlet to the instrument housing is of the order of 50 seconds.
The remote temperature sensor was supplied by water from the intake side of the non-toxic supply; i.e. the sea surface temperature was measured at near-ambient temperature free from any warming effects induced by the pumping system. The conductivity cell and housing temperature thermistor were supplied by a through-flow system from the non-toxic supply.
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 but were later 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 combined data set comprising discrete salinity measurements on samples taken either from the thermosalinograph outlet or from a water bottle sample collected at 5 m depth. A total of 44 samples were considered and showed the thermosalinograph to be reading 0.021 PSU low. The standard deviation in the offset was 0.03 PSU. No systematic variation in the offset was observed during the cruise.
The remote (i.e. sea surface) temperature was back calibrated against readings from a pair of SIS digital reversing thermometers mounted on a water bottle fired at 5 m depth. A total of 22 samples were considered which showed the thermosalinograph to be reading 0.028°C high. The standard deviation of the offset was 0.072°C. No systematic variation in the offset was observed during the cruise.
These offsets have been applied to the data.
The thermosalinograph generally worked well on this 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.
Fofonoff, N.P. and Millard Jr., R.C. (1983). Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science 44.
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)
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:
- 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)
- OXICOA, Oxidising Capacity of the Ocean Atmosphere - a study of the tropospheric ozone budget and underlying chemistry
- 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
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 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 Eastern Atlantic Experiment (EAE)
The Eastern Atlantic Experiment was a part 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 quantify input of DMS into a parcel of air
- To examine the oxidation of DMS and its reaction with nitrogen species with time
- To investigate the formation of new particles as a result of these transformations
- To discriminate between the natural and anthropogenic fractions of sulphur and nitrogen using isotopic measurements
The experiment included two campaigns in the spring seasons of 1996 and 1997, each of which incorporated three elements:
- A land-based site at Mace Head (at the seaward end of Galway Bay)
- A research vessel operating off the west coast of Ireland (RRS Challenger)
- Research aircraft overflights to link shipborne and land-based measurements
The primary measurements made during the campaigns were concentrations of DMS in the atmosphere and the water column, but a wide range of additional measurements were made including:
- Atmospheric ozone and nitrogen species
- Atmospheric particulates and their chemistry
- Atmospheric nitrogen and sulphur isotopic composition
- Oceanic temperature, salinity, attenuance and chlorophyll
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.
|Principal Scientist(s)||Lucinda Spokes (University of East Anglia School of Environmental Sciences)|
Complete Cruise Metadata Report is available here
No Fixed Station Information held for the Series
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|<||Below detection limit|
|>||In excess of quoted value|
|A||Taxonomic flag for affinis (aff.)|
|B||Beginning of CTD Down/Up Cast|
|C||Taxonomic flag for confer (cf.)|
|E||End of CTD Down/Up Cast|
|G||Non-taxonomic biological characteristic uncertainty|
|I||Taxonomic flag for single species (sp.)|
|K||Improbable value - unknown quality control source|
|L||Improbable value - originator's quality control|
|M||Improbable value - BODC quality control|
|O||Improbable value - user quality control|
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|0||no quality control|
|2||probably good value|
|3||probably bad value|
|6||value below detection|
|7||value in excess|
|A||value phenomenon uncertain|
|Q||value below limit of quantification|