Metadata Report for BODC Series Reference Number 610086

• 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

Kongsberg Simrad EA500 bathymetric echosounder

The EA500 is a bathymetric echosounder that can be used in water as deep as 10,000 m. It features triple frequency operation with a separate digitiser for each channel and high transmitted power with an instantaneous dynamic range of 160 dB. The instrument can operate with several pulses in the water simultaneously and has bottom tracking capabilities. A wide range of transducers (single beam, split beam or side-looking) is available and the ping rate is adjustable up to 10 pings per second. The split beam operation measures the athwartships inclination angle of the seabed.

This instrument was introduced in June 1989 and and replaced by the EA 600 in 2000.

Specifications

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

Aquatracka fluorometer

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.

Gill Instruments Ltd Ultrasonic 3-Axis Anemometers

The Gill R3-series 3D ultrasonic anemometers measure winds at high frequency in the speed range 0-45 m s^-1, and direction range 0-359°C. The instruments are of aluminium and carbon fibre construction, and operate at temperatures from -40°C to +60°C.

The R3-series anemometers have vertical head alignment. The sensor head incorporates an array of three pairs of transducers. Each transducer in a pair alternately transmits and receives ultrasound pulses to and from its partner. The travel times of the pulses are used to infer the velocity component of air flow along the line of the transducer pair. The transducer pairs are orthogonal to each other, alowing determination of the 3D resultant wind from the three wind vectors.

The R3-50 anemometer measures wind speed and direction at a rate of 50 Hz, while the R3-100 and th R3A-100 measure at a rate of 100 Hz. The sensor heads of the R3-50 and R3-100 have third order rotational symmetry. The sensor head of the R3A-100 is asymmetric, to minimise disturbance of the prevailing wind. Otherwise, the R3-100 and the R3A-100 are identical.

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 Temperature and Relative Humidity HMP Sensors

A family of sensors and instruments (sensors plus integral displays or loggers) for the measurement of air temperature and relative humidity. All are based on a probe containing a patent (HUMICAP) capacitive thin polymer film capacitanece humidity sensor and a Pt100 platinum resistance thermometer. The probes are available with a wide range of packaging, cabling and interface options all of which have designations of the form HMPnn or HMPnnn such as HMP45 and HMP230. Vaisala sensors are incorporated into weather stations and marketed by Campbell Scientific.

All versions operate at up to 100% humidity. Operating temperature ranges vary between models, allowing users to select the version best suited to their requirements.

Further details can be found in the manufacturer's specification sheets for the HMP 45 series, HMP 70 series and HMP 230 series.

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.

Chelsea Technologies Photosynthetically Active Radiation (PAR) Irradiance Sensor

This sensor was originally designed to assist the study of marine photosynthesis. With the use of logarithmic amplication, the sensor covers a range of 6 orders of magnitude, which avoids setting up the sensor range for the expected signal level for different ambient conditions.

The sensor consists of a hollow PTFE 2-pi collector supported by a clear acetal dome diverting light to a filter and photodiode from which a cosine response is obtained. The sensor can be used in moorings, profiling or deployed in towed vehicles and can measure both upwelling and downwelling light.

Specifications

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

Global Positioning Satellite System

A location system of unspecified make or model that determines location on the Earth's surface using the Global Positioning Satellite Network. Angular co-ordinates are given relative to WGS84 CRS. Other parameters such as platform velocity may be derived from this.

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

RRS Challenger CH127/96 Underway Instrumentation

Navigation

• Global Positioning System (GPS)
• Ship's gyro
• Electro Magnetic Log
• Echo Sounder

Meteorology

• Port and starboard solar radiation meters
• Port and starboard 2-pi PAR irradiance meters
• Port and starboard planar PAR radiance sensors
• Port and starboard psychrometers
• Humidity sensor
• Conventional cup and vane anemometer
• Sonic anemometer
• Aneroid 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 several minutes.

The level C includes 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. The instrument windows were cleaned daily and the tank was regularly flushed with detergent to prevent the development of marine fouling. Note that the detergent used was fluorescent and provided a signal similar to high chlorophyll concentrations. A log was kept of the tank flushing times and the data from these times have been flagged suspect.

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. Very little data required flagging other than during instrument maintenance and the interruption to the non-toxic supply for a boat transfer on June 13th.

A data set of 403 fluorometrically assayed extracted chlorophyll samples analysed at the University of East Anglia were made available for fluorometer calibration. These were taken approximately half-hourly over a 12-hour period from midday to midnight for most of the cruise duration. They therefore form an ideal calibration data set. Regressing the log of the extracted chlorophyll values against contemporaneous fluorometer voltages (available for 401 or the 403 samples) gave the calibration equation:

• chlorophyll = exp (0.9876*Volts - 2.5573) (n=401: R²=65%)

Examination of the residuals showed a skewed distribution towards underestimation by the fluorometer that is characteristic of quenching (reduced fluorescence yield at high light levels). Further, the residuals exhibited a significant (R=0.5) correlation with PAR. The log chlorophyll values for which PAR irradiance data were available (331 of the 401 samples) were therefore regressed against voltage and PAR giving the equation:

• chlorophyll = exp (1.2782*Volts + 0.001803*PAR - 3.5352) (n=331, R²=77%)

Examination of the residuals after the multiple regression showed a normal distribution with the mean error reduced from -0.0179 (standard deviation 0.4131) to 0.0032 (standard deviation 0.3175). The second equation has therefore been used to compute the calibrated chlorophyll channel provided in the data set. The raw voltage channel has been left in the data file to allow alternative calibrations to be used if desired.

Meteorology - Air Temperature and Humidity Processing

Temperature

Two Vector Instruments psychrometers were fitted to the port and starboard sides of the foremast together with a Vaisala low grade temperature and humidity sensor mounted between them. The Vaisala generated output in engineering units (C and %) whilst the psychrometers output voltages which were converted to temperatures using the manufacturer's calibrations thus:

The data were logged every 5 seconds but were later reduced to 1 minute intervals by averaging at BODC. The four psychrometer channels plus the two channels from the Vaisala were visually inspected on a graphics workstation, any obvious problems affecting one of the psychrometers but not the other were flagged as suspect. The Vaisala temperature channel was inspected in conjunction as an independent check on the psychrometers. In general, the agreement between all temperature sensors was very good (usually within 0.1°C with occasional differences up to 0.5°C) until the Vaisala temperature sensor developed serious problems at approximately 18:00 on June 27th.

Combined dry and wet bulb temperature channels were generated by averaging the data from the port and starboard instruments. The merged channels were then inspected on a graphics workstation. A number of noisy high temperature events affecting all sensors were identified in the record. Where these correlated with wind on the stern (relative wind direction between 45 and 135 for the way the conventional anemometer was mounted on Challenger) or changes in the ship's course they were attributed to stack thermal pollution and flagged suspect.

Humidity

Inspection of the Vaisala humidity channel revealed a number of large spikes plus periods when the data were obviously affected by the stack pollution events described above. These have all been flagged as suspect.

Please note that the Vaisala humidity channel has been included as a convenient direct source of humidity data. It is however a low grade instrument, with possible accuracy limitations, as readings (not spikes) of up to 104 per cent reveal . Humidity may be computed from the wet and dry bulb temperature data as an alternative if required.

Meteorology - Barometric Pressure Processing Notes

A Vaisala aneroid barometer was mounted on the foremast platform. The instrument output data in millibars which was logged every 5 seconds these data were later 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.

Meteorology - Photosynthetically Available Radiation (PAR) Processing

PML designed 2-pi PAR irradiance 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 shaded the instrument.

The sensors were logged as voltages every 30 seconds. These were averaged to 1 minute values and calibrated in W m^-2 by BODC using coefficients determined in July 1995. The calibration equations used were:

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.

During the cruise a problem with the analogue board of the data logging system caused the data from the starboard instrument to be lost for the following periods:

• 16:33 on June 7th to 21:05 on June 7th
• 08:30 on June 8th to 22:26 on June 9th
• 11:15 on June 10th to 14:24 on June 18th

During these periods there is a greater chance of the merged irradiance channel being low due to shading of the port sensor. This problem is not too severe as the port mounting on Challenger is less susceptible to shading. However, there is evidence (in the form of a step in the data) that the port sensor was shaded shortly before the problem was fixed on June 18th .

Meteorology - Photosynthetically Available Radiation (PAR) Processing Notes

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 the voltages were converted to W m^-2 from volts using the following 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 Notes

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. At the start of the cruise, only one instrument was carried in the port mounting. The second (Serial number 871026) was brought on the cruise and successfully fitted to the starboard mounting at about 10 am on June 8th, its location was far from ideal due to a large satellite communication radome which frequently shaded the instrument. The sensors were cleaned daily during the cruise. The instruments were connected to a data integrator which converted the instrument voltages to W m ^-2 and integrated the values producing 10 minute and running total integrations in kJ m ^-2 .

At BODC, the ten minute integrations were merged into the underway file using custom software which divided the integrated energy by the integration interval thus producing an average irradiance value. The time stamp was also adjusted to the mid-point of the averaging interval by subtracting five minutes.

During the cruise, a problem was discovered with the integrator calibrations. Although the port and starboard sensors had been exchanged, the calibrations had not been changed. Further, the calibration values had not been updated to bring them into line with the July 1995 sensor recalibration. This was corrected at 14:12 on June 22nd. Up until this time, the port instrument voltage had been divided by 12.36 instead of 12.66 and the starboard instrument voltage had been divided by 12.76 instead of 12.30. The problem was corrected at BODC by multiplying the affected data by 1.037398 (starboard) and 0.9763033 (port).

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 conventional Vaisala cup and vane anemometer and a sonic anemometer operated by Southampton Oceanography Centre (SOC) were mounted on the meteorological package platform on the foremast (approximately 12m above sea level) with the sonic anemometer central and forward of the conventional anemometer which had the cup to port and the vane to starboard. The cup and vane were at the same height as the mid-point of the sonic instrument. The Vaisala vane was mounted with zero to starboard and the sonic anemometer was mounted with a 30 degree offset to port (i.e. if 180 degrees is the relative wind direction for wind blowing directly over the bows of the ship, then the v component is positive from 150 through 330 degrees and the u component is positive when the wind is between 60 and 240 degrees). A SOC comparison of the relative directions from the two instruments indicates that the offset between the zero points is 110 degrees whereas the expected value is 120 degrees.

The objective of the data processing is to generate definitive wind speed and wind direction. These have been generated from the conventional anemometer to ensure comparability with other cruises where the sonic instrument may not be carried. However, the sonic data were temporarily merged into the data file to allow comparative screening of the relative wind speeds. The additional information it provided (vertical wind velocity) is retained.

The cup anemometer generated relative wind speed in m/s and relative wind direction in degrees which were logged every 5 seconds and 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). These data were visually examined on a graphics workstation and suspect values flagged.

The ship's heading was added to the relative wind direction and 260 degrees subtracted to correct for the vane orientation. Note that this assumes that it was the sonic instrument that was correctly oriented due to its more robust mechanical mounting. 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 again 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.

The sonic anemometer provided three wind component velocities (port/starboard, fore/aft and vertical) as voltages such that (manufacturer's calibration):

The jumper settings in the instrument were set to give a full scale reading of 30 m/s. Voltages were logged every 30 seconds and the voltages were converted to velocities in knots using the equation:

• Velocity = Volts*23.28 - 58.2

The data were reduced to 1 minute sampling at BODC by averaging. Comparison of the raw wind speeds from the two instruments showed exceptionally good agreement. Most of the time they were well within 0.5 knots with a maximum observed difference of 2 knots. No further comparisons on the raw wind direction beyond the work at SOC were undertaken.

The vertical wind velocity from the sonic instrument was inspected on a graphics workstation and a small number of obvious spikes were flagged suspect.

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

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 daily and the tank was frequently washed out with Decon90 to prevent the development of marine fouling.

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. This was based on an air reading of 4.700V taken on June 12th after careful cleaning of the instrument optics and the manufacturer's air reading of 4.789V. Blocked path readings by the manufacturer and during the cruise were zero.

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 data set to be extremely noisy at times due to bubbles forming in the non-toxic system during rough weather. These have been flagged out together with other problem data resulting from the interruption to the non-toxic supply for a boat transfer on June 13th.

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 an Ocean Data Equipment Corporation (ODEC) model TSG 103 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 this was 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. This included a short period (12:27 to 13:40 on 13th June) when the non-toxic supply was switched off to facilitate a boat transfer off Galway.

Salinity

Salinity was back calibrated using a set of discrete salinity measurements on samples taken from the thermosalinograph outlet. A total of 152 samples were takes at approximately 2-hourly intervals during the working day between 08:00 and 23:00.

Analysis of the differences between thermosalinograph and bottle salinities revealed that the instrument was initially reading 0.06 low until it was cleaned out at 09:30 on June 6th. After cleaning, the offset was 0.063 which quickly settled to a mean offset of 0.052 (mean of 51 samples: standard deviation 0.005). This remained constant until June 16th when a linear increase in offset magnitude was observed. The rate of change increased as the cruise progressed. During the evening of July 2nd, 5 discrete jumps in the offset were observed which coincided with the powering down of the electrical load on the ship's 110V supply. Whether this was coincidence or cause and effect is not known.

The salinity calibration was modelled by the equation:

• Corrected salinity = Raw salinity + (cycle_number * Slope) + Offset

This correction model has been applied to the data with the following coefficients.

Temperature

The remote (i.e. sea surface) temperature was back calibrated against readings from the SeaBird SBE25 CTD which was held at the non-toxic inlet depth on each cast whilst a thermosalinograph temperature reading was logged manually. This showed the thermosalinograph to be reading 0.083 C low at the start of the cruise which drifted linearly to 0.139 C low by the end of the cruise. The correction required has been modelled by the equation:

• Corrected T = Raw T + (0.0000013543854*cycle_number) + 0.08323884

There was, however, a complication. A UV irradiator brought by the team from Dalhousie required a UK plug which was fitted with the earth and neutral wired the wrong way round. The resulting electrical interference caused the sea surface temperature to drop by up to 0.08C each time the irradiator was switched on, normally a couple of times a day. A correction was implemented by modifying the calibration for the affected periods. Individual offsets, ranging from 0.05C to 0.08C, were computed for each interference event and added to the calibration intercept as detailed below:

The problem was noticed on June 25th and the cause identified and corrected early on the 26th. Extensive testing showed it to be cured. However, it can be seen that there was a recurrence, attributed to a poor electrical connection in the irradiator plug, on July 2nd.

All the temperature corrections described above have been applied to the data.

Data quality Report

The thermosalinograph generally worked well on this cruise. There are, however, two features of the data set which are worthy of note. First, there are periods of temperature noise reaching an amplitude of nearly a degree at times. These 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. In contrast there are a small number of noisy periods in the salinity record that are believed to result from electrical interference (source unidentified). These have been heavily flagged to minimise the amplitude of the noise.

Reference

Fofonoff, N.P. and Millard Jr., R.C. (1983). Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science 44.

TOOL0582 Vector Instruments H301 psychrometer

The H301 Aspirated Psychrometer is an aspirated humidity sensor using the "Wet and Dry Bulb" method for reliable determination of air temperature and relative humidity.

The instrument construction is weather resistant while retaining easy access to the sensing elements for calibration, cleaning and wick replacement.

A long-life motor/fan ensures a high air flow past the sensing elements for an accurate wet-bulb depression.

A pair of 100 Ohm 4-terminal platinum resistance elements (RTD/PRT) are used as the sensing elements.

A 500ml water reservoir provides for over 7 days continuous operation.

Discontinued in 2010.

Please click here to see more information from Windspeed Ltd./Vector Instruments regarding the H301 psychrometer.

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 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
• Meteorology

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: