Metadata Report for BODC Series Reference Number 787268


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 lowered unmanned submersible
Originating Country United Kingdom
Originator Mr John Howarth
Originating Organization Proudman Oceanographic Laboratory (now National Oceanography Centre, Liverpool)
Processing Status banked
Project(s) Provess
 

Data Identifiers

Originator's Identifier CTD48
BODC Series Reference 787268
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1998-11-05 00:52
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 1.0 decibars
 

Spatial Co-ordinates

Latitude 58.83100 N ( 58° 49.9' N )
Longitude 1.02483 E ( 1° 1.5' E )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor Depth 1.49 m
Maximum Sensor Depth 107.46 m
Minimum Sensor Height 7.54 m
Maximum Sensor Height 113.51 m
Sea Floor Depth 115.0 m
Sensor Distribution Variable common depth - All sensors are grouped effectively at the same depth, but this depth varies significantly during the series
Sensor 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 CODE Rank Units Short Title Title
ATTNMR01 1 per metre Atten_red Attenuation (red light wavelength) per unit length of the water body by 20 or 25cm path length transmissometer
CPHLPR01 1 Milligrams per cubic metre chl-a_water_ISfluor Concentration of chlorophyll-a {chl-a CAS 479-61-8} per unit volume of the water body [particulate >unknown phase] by in-situ chlorophyll fluorometer
FVLTAQ01 1 Volts AqVolt Instrument output (voltage) by in-situ Aquatracka chlorophyll fluorometer
IRRDPP01 1 MicroEinsteins per square metre per second DwIrr_2-piPAR Downwelling 2-pi scalar irradiance as photons (PAR wavelengths) in the water body by 2-pi scalar radiometer
POTMCV01 1 Degrees Celsius WC_Potemp Potential temperature of the water body by computation using UNESCO 1983 algorithm
PRESPR01 1 Decibars Pres_Z Pressure (spatial co-ordinate) exerted by the water body by profiling pressure sensor and corrected to read zero at sea level
PSALCC01 1 Dimensionless P_sal_CTD_calib Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm and calibration against independent measurements
SIGTPR01 1 Kilograms per cubic metre SigTheta Sigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm
TEMPST01 1 Degrees Celsius WC_temp_CTD Temperature of the water body by CTD or STD
TSEDTR01 1 Milligrams per litre TSPMTr Concentration of suspended particulate material {SPM} per unit volume of the water body [particulate >unknown phase] by in-situ optical attenuance measurement and calibration against sample data
 

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

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 140 CTD Data Documentation

Cruise Principal Scientist

John Howarth, Proudman Oceanographic Laboratory (POL), Merseyside, UK.

Data Originators

British Oceanographic Data Centre, POL, Merseyside, UK.
Research Vessel Services, SOC, Southampton, UK.

Content of data series

Parameter Unit Parameter code Number of stations Comments
Pressure db PRESPR01 60 none
Salinity PSU-78 PSALCC01 60 none
Temperature deg. C TEMPST01 60 none
Potential temperature (UNESCO) deg. C POTMCV01 60 none
Sigma-theta (UNESCO SVAN) kg m -3 SIGTPR01 60 none
Chlorophyll a µg l -1 CPHLPR01 42 calibrated from fluorometer voltages caution (see text)
Raw fluorometer voltages volts FVLTAQ01 60 none
Optical attenuance m -1 ATTNMR01 60 none
Total suspended sediment mg l -1 TSEDTR01 60 calibrated from attenuance caution (see text)
Dissolved oxygen µmol l -1 DOXYPR01 31 caution (see text)
Oxygen saturation percent OXYSBB01 31 caution (see text)
Downwelling PAR µE m -2 s -1 IRRDPP01 60 none
Upwelling PAR µE m -2 s -1 IRRUPP01 60 none

Instrumentation and data processing by originator

CTD unit and auxiliary sensors

RVS Neil Brown Mk3B CTD incorporating a pressure sensor, a conductivity cell, a platinum resistence thermometer, a 20 cm pathlength SeaTech transmissometer (660 nm), a Mk II Aquatracka fluorometer, two 2PI PAR light meters for upwelling and downwelling irradiance and a Beckman dissolved oxygen sensor fed by a Seabird 5T submersible pump.

Changes of sensors during the cruise

Data acquisition

The CTD was first lowered down to a depth of approx. 10 m where it was left for a few minutes before being brought back to just below sea surface. This was necessary to activate the SeaBird pump. It was then lowered continuously at 0.5 to 1 m s -1 to the closest comfortable proximity to the sea floor. The upcast was done in stages between bottle firing depths.

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

On-board data processing

The raw data (ADC counts) were converted into engineering units (volts for PAR meters, for fluorometers and transmissometers; ml/l for oxygen; mmho/cm 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). PAR volts were converted to µWatts cm -2

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.

Sampling device

The CTD unit was protected by a metallic frame. A General Oceanic rosette sampler equipped with twelve 30-litre Niskin water bottles was fitted above the frame. The base of the bottles was at 0.75 metres above the pressure head and their tops at 1.55 m above it. One bottle was fitted with a holder for twin digital reversing thermometers mounted 1.40 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.

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

BODC post-cruise processing and screening

Reformatting

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

% transmission= Volts * 20 * Va / Vb (1)
attenuance (m -1 ) = -1 / PL * log e (% transmission / 100) (2)

where Va is the manufacturer's air reading for this instrument, Vb is the average of the air readings carried out during the cruise and PL is the transmissometer pathlength in metres (0.20 m).

Screening

Reformatted CTD data were transferred onto a high-speed graphics workstation. Using custom in-house graphics editor SERPLO, downcasts and upcasts were differentiated and the limits of the downcasts and upcasts were manually flagged. If present, spikes and suspicious data 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 to 'M' for suspicious values and 'N' for null.

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.

Banking

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.

P corr = P - 1.13 (standard deviation 0.36 db)
T corr = T + 0.022 (standard deviation 0.002)

A significant offset in the difference between CTD-salinity and salinometer-salinity was observed between the first leg (24-28 Oct.) and second leg (1-7 Nov.) of the cruise. As a result two different corrections have been applied to the following groups of CTD casts:

CTD01 to CTD18: S corr = S - 0.030 (standard deviation 0.003)
CTD19 to CTD60: S corr = S - 0.039 (standard deviation 0.002)

Upwelling and downwelling irradiance: the PAR voltages were converted to W m -2 using the following equations determined in August 1995 and supplied by RVS:

Downwelling (#12): PAR (W m -2 ) = exp (-4.92*volts + 6.506)/100
Upwelling (#11): PAR (W m -2 ) = exp (-5.00*volts + 6.536)/100

The data were then converted from W m -2 into µE m -2 s -1 (22/12/1998) by applying a multiplication factor of 3.75. This factor is derived from an empirical calibration of the 2PI PAR sensors.

T-1022-D (all casts except CTD03):
manufacturer's air reading = 4.662 volts
air reading = 4.656 volts
blocked light path reading = 0.000 volts
T-1019-D (CTD03):
manufacturer's air reading = 4.682 volts
air reading not available (used manufacturer's air reading)
blocked light path reading = 0.002 volts

The air correction was applied during the transfer of the ASCII data into PXF (see above). The data stored in the database are therefore calibrated.

TSED (mg l -1 ) = (ATTN - 0.39557) / 0.46891, R 2 =0.373, n=62

For the third group the noise in the data was such that it was deemed impossible to calibrate the data. The whole fluorescence profile was therefore flagged suspect and no chlorophyll concentration was derived.

For the remaining profiles, the calibration dataset was composed of 49 measurements of extracted chlorophyll (data originator: K. Jones, DML, UK) of which 28 were associated with low voltages fluorometer output and 21 with high voltages fluorometer output. The range of chlorophyll concentration was quite low in both groups ranging from 0 to 0.54 µg l -1 in the low voltage group and 0 to 0.57 µg l -1 in the high voltage group. The calibration equations applied are as follows:

Low voltage group: Chl = exp (12.59 FV - 10.54), R 2 =0.278, n=15
High voltage group: Chl = exp (5.72 FV - 10.02), R 2 =0.744, n=14

where Chl = predicted chlorophyll a concentration in µg l -1 and FV= CTD fluorometer voltage. Note that null values for chlorophyll concentration had to be excluded in order to calculate the logarithmic fit. Residuals from the regressions ranged from -0.25 to +0.29 µg l -1 for the first group and from -0.23 to +0.25 µg l -1 for the second. Both residuals and predicted values were examined graphically for skewness. The distribution of the regression residuals were also examined against sample depths and in situ irradiance but no significant trends were observed.

Oxygen concentration measurements by Winkler titration were performed on samples taken from eight depths on casts 02, 05 and 14 (data originator: K. Jones, DML, UK). Because of the problems encountered with the CTD oxygen probe on casts 02 and 14 calibration could only be derived using data from cast 05. The calibration equation derived is as follows:

Oxygen= 4.20 CTD_oxygen - 227.70, R 2 = 0.889, n=8

Considering that this calibration was derived from one profile only, users are advised to use the calibrated oxygen CTD data with caution.

Comments on data quality


Project Information

PROcesses of Vertical Exchange in Shelf Seas (PROVESS)

Introduction

PROVESS was an interdisciplinary study of the vertical fluxes of properties through the water column and the surface and bottom boundary layers. The project was funded by the European Community MAST-III programme (MAS3-CT97- 0159) and ran from March 1998 to May 2001.

Scientific Rationale

PROVESS was based on the integration of experimental, theoretical and modelling studies with the aim of improving understanding and quantification of vertical exchange processes in the water column, in particular in the surface and benthic boundary layers and across the> pycnocline. PROVESS also explored mechanisms of physical-biological coupling in which vertical exchanges and turbulence significantly affect the environmental conditions experienced by the biota with particular reference to aggregation, flocculation, sedimentation and trophic interactions.

Fieldwork

The experimental phase of the project was carried out at two contrasting sites in the North Sea: the northern North Sea site (NNS) and the southern North Sea site (SNS).

The two sites had the following characteristics:

SNS NNS
Position 52° 15.0' N, 4° 17.0' E 59° 20.0' E, 1° 00.0' E
Time of year April-May September-November
Water depth (m) 16 100
M2 max amplitude (m s-1) 0.75 0.15
Max current (m s-1) 1.0 0.6
Delta T (deg C) mixed 7-1
Thermocline depth (m) mixed 35-100
Delta S 1 small
Halocline depth (m) 5-10 cf. thermocline depth
Max wind speed (m s-1) 20 25
Max wave height (m) 5 10
Max wave period (s) 8 10
Internal motion No Yes
Sediment muddy-sand muddy-sand
Biology eutrophic oligotrophic

At both locations measurements were concentrated at a central position with additional measurements being made to estimate horizontal gradients. Moored instruments (including current meters, temperature and pressure sensors, fluorometers, transmissometers, nutrient analysers and meteorological sensors) were deployed between 7 September and 5 November 1998 at the NNS and between 29 March and 25 May 1999 at the SNS. Each experiment was supported by intensive measurement series made from oceanographic ships and involving turbulence dissipation profiler CTD, particle size profilers, optical profilers, benthic sampling and water bottle sampling.

Details of the cruises were as follows:

Site Ship
(nationality)
Cruise
Mnemonic
Date
NNS Valdivia (GER) VA174 5 - 17 Sep 1998
  Dana (DK) D1198 14 - 26 Oct 1998
  Pelagia (NL) PE125 19 - 30 Oct 1998
  Challenger (UK) CH140 22 Oct - 9 Nov 1998
SNS Pelagia (NL) PE135 29 Mar - 9 Apr 1999
  Mitra (NL) MT0499 19 - 30 Apr 1999
  Belgica (BE) BG9912 17 - 21 May 1999

Data Activity or Cruise Information

Cruise

Cruise Name CH140 (PROVESS N-4)
Departure Date 1998-10-21
Arrival Date 1998-11-11
Principal Scientist(s)M John Howarth (Proudman Oceanographic Laboratory)
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