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Metadata Report for BODC Series Reference Number 858253


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Neil Brown MK3 CTD  CTD; water temperature sensor; salinity sensor; dissolved gas sensors
SeaTech transmissometer  transmissometers
Chelsea Technologies Group Aquatracka fluorometer  fluorometers
Chelsea Technologies Group 2-pi PAR irradiance sensor  radiometers
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Prof Paul Tett
Originating Organization Napier University School of Life Sciences (now Edinburgh Napier University School of Life, Sport & Social Sciences)
Processing Status banked
Online delivery of data Download available - Ocean Data View (ODV) format
Project(s) Land Ocean Interaction Study (LOIS)
 

Data Identifiers

Originator's Identifier CP40
BODC Series Reference 858253
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1996-04-25 05:04
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 2.0 decibars
 

Spatial Co-ordinates

Latitude 56.00033 N ( 56° 0.0' N )
Longitude 8.25200 W ( 8° 15.1' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor or Sampling Depth 2.97 m
Maximum Sensor or Sampling Depth 149.57 m
Minimum Sensor or Sampling Height 8.33 m
Maximum Sensor or Sampling Height 154.93 m
Sea Floor Depth 157.9 m
Sea Floor Depth Source DATAHEAD
Sensor or Sampling Distribution Variable common depth - All sensors are grouped effectively at the same depth, but this depth varies significantly during the series
Sensor or Sampling Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
Sea Floor Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
 

Parameters

BODC CODERankUnitsTitle
ATTNZR011per metreAttenuation (red light wavelength) per unit length of the water body by transmissometer
CPHLPR011Milligrams per cubic metreConcentration of chlorophyll-a {chl-a CAS 479-61-8} per unit volume of the water body [particulate >unknown phase] by in-situ chlorophyll fluorometer
IRRDPP011MicroEinsteins per square metre per secondDownwelling 2-pi scalar irradiance as photons of electromagnetic radiation (PAR wavelengths) in the water body by 2-pi scalar radiometer
POATCV011per metrePotential attenuance (unspecified wavelength) per unit length of the water body by transmissometer and computation using P-EXEC algorithm
POTMCV011Degrees CelsiusPotential temperature of the water body by computation using UNESCO 1983 algorithm
PRESPR011DecibarsPressure (spatial coordinate) exerted by the water body by profiling pressure sensor and correction to read zero at sea level
PSALST011DimensionlessPractical salinity of the water body by CTD and computation using UNESCO 1983 algorithm
SIGTPR011Kilograms per cubic metreSigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm
TEMPST011Degrees CelsiusTemperature of the water body by CTD or STD

Definition of Rank

  • Rank 1 is a one-dimensional parameter
  • Rank 2 is a two-dimensional parameter
  • Rank 0 is a one-dimensional parameter describing the second dimension of a two-dimensional parameter (e.g. bin depths for moored ADCP data)

Problem Reports

No Problem Report Found in the Database


Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."


Narrative Documents

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

Specifications

These specification apply to the MK3C version.

Pressure Temperature Conductivity
Range

6500 m

3200 m (optional)

-3 to 32°C 1 to 6.5 S cm-1
Accuracy

0.0015% FS

0.03% FS < 1 msec

0.0005°C

0.003°C < 30 msec

0.0001 S cm-1

0.0003 S cm-1 < 30 msec

Further details can be found in the 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.

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

Operation depth 1000 m
Range 2000 to 0.002 µE m-2 s-1
Angular Detection Range ± 130° from normal incidence
Relative Spectral Sensitivity

flat to ± 3% from 450 to 700 nm

down 8% of 400 nm and 36% at 350 nm

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

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.

RRS Challenger 126A CTD Data Documentation

Components of the CTD data set

The CTD data set for cruise CH126A consists of 45 vertical profiles containing the parameters temperature, salinity, upwelling and downwelling irradiance (on some casts), chlorophyll, and optical attenuance.

Data Acquisition and On-Board Processing

Instrumentation

The CTD profiles were taken with an RVS Neil Brown Mk3B CTD incorporating a pressure sensor, conductivity cell, platinum resistance thermometer and a Beckmann dissolved oxygen sensor. The CTD unit was mounted vertically in the centre of a protective cage approximately 1.5m square. Attached to the bars of the frame were a Chelsea Instruments Aquatracka fluorometer and a SeaTech red light (661 nm) transmissometer with a 25cm path length.

Above the frame was a General Oceanics rosette sampler fitted with twelve 10-litre Niskin bottles. The bases of the bottles were 0.75 metres above the pressure head and their tops 1.55 metres above it. One bottle was fitted with a holder for twin digital reversing thermometers mounted 1.38 metres above the CTD temperature sensor.

Above the rosette was a PML 2pi PAR (photosynthetically available radiation) sensor pointing upwards to measure downwelling irradiance. A second 2pi PAR sensor, pointing downwards, was fitted to the bottom of the cage to measure upwelling irradiance. It should be noted that these sensors were vertically separated by 2 metres with the upwelling sensor 0.2 metres below the pressure head and the downwelling sensor 1.75 metres above it.

No account has been taken of rig geometry in the compilation of the CTD data set. However, all water bottle sampling depths have been corrected for rig geometry and represent the true position of the midpoint of the water bottle in the water column.

Data Acquisition

On each cast, the CTD was lowered continuously at 0.5 to 1.0 m s-1 to the closest comfortable proximity to the sea floor. The upcast was done in stages between the bottle firing depths.

Data were logged by the RVS ABC data logging system. Output channels from the deck unit were logged at 32 Hz by a microprocessor interface (the Level A) which passed time-stamped averaged cycles at 1 Hz to a Sun workstation (the Level C) via a buffering system (the Level B).

On-Board Data Processing

The raw data comprised ADC counts. These were converted into engineering units (volts for PAR meters, fluorometer and transmissometer; ml l-1 for oxygen; mmho cm-1 for conductivity; °C for temperature; decibars for pressure) by the application of laboratory determined calibrations. Salinity (Practical Salinity Units as defined in Fofonoff and Millard, 1983) was calculated from the conductivity ratios (conductivity/42.914) and a time lagged temperature using the function described in UNESCO Report 37 (1981).

The data set was submitted to BODC in this form on Quarter Inch Cartridge tapes in RVS internal format for post-cruise processing and data banking.

Post-Cruise Processing and Calibration at BODC

Reformatting

The data were converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the workstation graphics editor. In addition to reformatting, the transfer program applied the following modifications to the data:

  • Dissolved oxygen was converted from ml l-1 to µM by multiplying the values by 44.66.
  • Transmissometer voltages were corrected to the manufacturer's specified voltage by ratio using transmissometer air readings taken during the cruise.
  • Transmissometer voltages were converted to percentage transmission by multiplying them by a factor of 20.
  • The transmissometer data were converted to attenuance using the algorithm:-
Attenuance (m-1) = -4 loge (% transmission/100)

Editing

Reformatted CTD data were transferred onto a high-speed graphics workstation. Using custom in-house graphics editors, downcasts and upcasts were differentiated and the limits of the downcasts and upcasts were manually flagged.

Spikes on all the downcast channels were manually flagged. No data values were edited or deleted; flagging was achieved by modification of the associated quality control flag.

The pressure ranges over which the bottle samples had been collected were logged by manual interaction with the software. Usually, the marked reaction of the oxygen sensor to the bottle firing sequence was used to determine this. These pressure ranges were subsequently used, in conjunction with a geometrical correction for the position of the water bottles with respect to the CTD pressure transducer, to determine the pressure range of data to be averaged for calibration values.

Once screened on the workstation, the CTD downcasts were loaded into a database under the ORACLE Relational Database Management System.

Calibration

With the exception of pressure, calibrations were done by comparison of CTD data against measurements made on water bottle samples or from the reversing thermometers mounted on the water bottles as in the case of temperature. In general, values were averaged from the CTD downcasts but where visual inspection of the data showed significant hysteresis values were manually extracted from the CTD upcasts.

All calibrations described here have been applied to the data.

Pressure

The pressure offset was determined by looking at the pressures recorded when the CTD was clearly logging in air (readily apparent from the conductivity channel). A consistent air reading was exhibited and the following correction applied:

Pcorr = P - 2.91 (standard deviation 0.17 dbar)
Temperature

The CTD temperature was compared with the digital reversing thermometers attached to the water bottles. The two instruments were found to agree within 0.001 °C. Hence no correction has been applied to the CTD temperature data.

Salinity

Salinity was calibrated against water bottle samples measured on the Guildline 55358 AutoLab Salinometer during the cruise.

Samples were collected in glass bottles filled to just below the neck and sealed with plastic stoppers. Batches of samples were left for at least 24 hours to reach thermal equilibrium in the lab containing the salinometer before analysis.

The correction applied for this cruise was:

Scorr = S + 0.027 (standard deviation 0.003)
Upwelling and Downwelling Irradiance

The PAR voltages were converted to W m-2 using the following equations determined in August 1995 supplied by RVS.

Upwelling (#2): PAR (W m-2) = exp (-4.97*volts + 6.878)/100
Downwelling (#1): PAR (W m-2) = exp (-4.90*volts + 7.237)/100

Note that these sensors have been empirically calibrated to obtain a conversion from W/m2 into µE/m2/s, which may be effected by multiplying the data given by 3.75.

Optical Attenuance and Suspended Particulate Matter

The air correction applied for this cruise was based on an air reading obtained during cruise Challenger CH125B (4.622V). The Challenger CH125B value was used as no air readings were taken during this cruise. The manufacturer's voltage for the instrument used (SN103D) was 4.758V.

Reports were received from UWB that the clear water attenuance values measured by SN103D were anomalously high. A careful investigation was initiated to look at this problem. This involved examination of clear water attenuance values from casts deeper than 500 m and an inter-comparison of the surface attenuance values with contemporaneous data from the underway transmissometer. It must be stressed that this exercise was comparative, looking at differences in the relationship between the CTD and underway instruments. No attempt was made to render both data sets numerically identical as experience has shown that the mechanical effects of the pump on the suspended particulate material modify the attenuance of water in the non-toxic supply.

Further information on the pattern of corrections required was obtained by examination of the superimposed attenuance profiles from groups of series on a graphics editor.

As a result, the following corrections were derived and have been applied to the data:

Casts CP1 to CP17  -0.133 per metre
Casts CP26 to CP27  -0.064 per metre
Casts CP38 to CP45  -0.097 per metre

Large volume samples were taken for gravimetric analysis of the suspended particulate matter concentration. These were used to generate calibrations that expressed attenuance in terms of suspended particulate matter concentrations.

Robin McCandliss (University of Wales, Bangor) undertook this work, under the supervision of Sarah Jones. The optimal approach developed was to base the calibration on samples taken from near the seabed (i.e. those with the minimum content of fluorescent material). The data from all SES cruises where SPM samples were taken were pooled to derive the calibration equation:

SPM (mg/l) = (2.368*Atten) - 0.801 (R2 = 79%)

This calibration is valid for all SES cruises after and including cruise Charles Darwin CD93A. The clear water attenuance predicted by the equation is 0.336 per m, which agrees well with literature values.

No attempt has been made to replace attenuance by SPM concentration in the final data set. However, users may use the equation above to compute an estimated SPM channel from attenuance when required.

Chlorophyll

200 ml of seawater collected at several depths on each cast were filtered and the papers frozen for acetone extraction and fluorometric analysis on land. The sample data set for calibration purposes comprised 94 values in the range 0.01 to 3.92 mg m-3. The following relationship was found between extracted chlorophyll levels and corresponding fluorometer voltages:

Chlorophyll (mg/m3) = exp (1.11*volts - 2.96) (R2 = 86%, n =94)
Dissolved Oxygen

No Winkler titration data were available from this cruise for the calibration of the dissolved oxygen sensor. Consequently, no dissolved oxygen channel has been included in the final version of the data set.

Data Reduction

Once all screening and calibration procedures were completed, the data set was binned to 2 db (casts deeper than 100 db) or 1 db (casts shallower than 100 db). The binning algorithm excluded any data points flagged suspect and attempted linear interpolation over gaps up to 3 bins wide. If any gaps larger than this were encountered, the data in the gaps were set null.

Data Warnings

None.

Reference

Fofonoff N.P., and Millard Jr., R.C. 1982. Algorithms for Computation of Fundamental Properties of Seawater. UNESCO Technical Papers in Marine Science 44.


Project Information

Land Ocean Interaction Study (LOIS)

Introduction

The Land Ocean Interaction Study (LOIS) was a Community Research Project of the Natural Environment Research Council (NERC). The broad aim of LOIS was to gain an understanding of, and an ability to predict, the nature of environmental change in the coastal zone around the UK through an integrated study from the river catchments through to the shelf break.

LOIS was a collaborative, multidisciplinary study undertaken by scientists from NERC research laboratories and Higher Education institutions. The LOIS project was managed from NERC's Plymouth Marine Laboratory.

The project ran for six years from April 1992 until April 1998 with a further modelling and synthesis phase beginning in April 1998 and ending in April 2000.

Project Structure

LOIS consisted of the following components:

  • River-Atmosphere-Coast Study (RACS)
    • RACS(A) - Atmospheric sub-component
    • RACS(C) - Coasts sub-component
    • RACS(R) - Rivers sub-component
    • BIOTA - Terrestrial salt marsh study
  • Land Ocean Evolution Perspective Study (LOEPS)
  • Shelf-Edge Study (SES)
  • North Sea Modelling Study (NORMS)
  • Data Management (DATA)

Marine Fieldwork

Marine field data were collected between September 1993 and September 1997 as part of RACS(C) and SES. The RACS data were collected throughout this period from the estuaries and coastal waters of the UK North Sea coast from Great Yarmouth to the Tweed. The SES data were collected between March 1995 and September 1996 from the Hebridean slope. Both the RACS and SES data sets incorporate a broad spectrum of measurements collected using moored instruments and research vessel surveys.


Data Activity or Cruise Information

Cruise

Cruise Name CH126A
Departure Date 1996-04-11
Arrival Date 1996-04-26
Principal Scientist(s)Paul Tett (Napier University School of Life Sciences)
Ship RRS Challenger

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:

Flag Description
Blank Unqualified
< 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.)
D Thermometric depth
E End of CTD Down/Up Cast
G Non-taxonomic biological characteristic uncertainty
H Extrapolated value
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
N Null value
O Improbable value - user quality control
P Trace/calm
Q Indeterminate
R Replacement value
S Estimated value
T Interpolated value
U Uncalibrated
W Control value
X Excessive difference

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

Flag Description
0 no quality control
1 good value
2 probably good value
3 probably bad value
4 bad value
5 changed value
6 value below detection
7 value in excess
8 interpolated value
9 missing value
A value phenomenon uncertain
Q value below limit of quantification