Metadata Report for BODC Series Reference Number 742502

• 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

COR11/03 CTD Instrument Description

Falmouth Scientific Integrated CTD (ICTD) Profiler

The FSI ICTD is designed to collect high precision conductivity, temperature and pressure data with self calibrating electronics. This instrument can support five primary sensors (including up to three temperature sensors) and can be coupled with a water bottle sampler. The ICTD is equipped with a titanium housing rated to 7000 m and has a sampling rate of 32 Hz.

Three temperature sensors are available: primary platinum, redundant platinum and exposed thermistor. Any combination of these can be used in the primary channels. The instrument also has multiple RS-232 serial inputs for a variety of sensors including: ADCP, Benthos PSA-916 Altimeter and WetLabs SAFire. There are an additional eight DC input channels that can support virtually any sensor that has a DC output.

Specifications:

*Optional

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

Seapoint Chlorophyll Fluorometer

The Seapoint Chlorophyll Fluorometer (SCF) is a low power instrument for in situ measurements of chlorophyll a. The SCF uses modulated blue LED lamps and a blue excitation filter to excite chlorophyll a. The fluorescent light emitted by the chlorophyll a passes through a red emission filter and is detected by a silicon photodiode. The low level signal is then processed using synchronous demodulation circuitry which generates an output voltage proportional to chlorophyll a concentration. The SCF may be operated with or without a pump.

Sensor specifications, current at August 2006, are given in the table below. More information can be found at the manufacturer's web site.

Sensor Specifications

LI-COR LI-192 Underwater Quantum Sensor

The LI-192 Underwater Quantum Sensor is used to measure photosynthetic photon flux density and is cosine corrected. The sensor is often referred to as LI-192SA or LI-192SB (the LI-192SB model was superseded by LI-192SA). One of the main differences is that the LI-192SA model includes a built-in voltage output for interfacing with NexSens iSIC and SDL data loggers.

Sensor specifications, current at January 2012, are given in the table below. More information can be found in the manufacturer's LI-192SA andLI-192SB specification sheets.

Sensor Specifications

(Specifications apply to both models unless otherwise stated)

BODC Processing

The data arrived at BODC in one ASCII format file per cast. These files were reformatted to the BODC internal netCDF subset, QXF, using the transfer function 268. The following table shows how the variables within the ASCII files were mapped to the appropriate BODC parameter codes:

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, missing data by both setting the data to an appropriate value and setting the quality control flag.

COR11/03 CTD Originator's Data Processing

Sampling strategy

A total of 70 full depth CTD profiles were obtained during the cruise to the North Sea. For all stations water samples were collected for salinity analysis (using a Guildline salinometer) to derive a calibration for the CTD conductivity sensor. Two pairs of digital reversing thermometers were used to verify the calibration of the CTD temperature sensor.

A Seapoint fluorometer sensor, Seapoint turbidity sensor and a LICOR photosynthetically active radiation sensor (with a six-decade log amplifier) were fitted to the CTD rosette. Chlorophyll samples were collected from the water column to calibrate the fluorometer. Samples for suspended particulate matter analysis were used to calibrate the turbidity sensor.

Field Calibrations

Pressure

During the cruise, the 'on-deck' CTD pressure measurements immediately prior to the CTD unit being lowered into the water column were recorded. These 'on-deck' measurements were used to correct the recorded CTD pressure as follows:

P(corrected) = P(uncorrected) + dP;

    S/N 1322: dP = 0.4 decibars; S/N 1366: dP = 1.2 decibars

Temperature

The platinum resistance temperature sensor fitted to the CTD unit was calibrated against platinum resistance thermometers on 01/01/2003 and this was used to correct the temperature recorded by the CTD:

T(corrected) = T(uncorrected) + dT;

    where: dT = a*T(uncorrected)² + b*T(uncorrected) + c

    S/N 1322: a = -4.2313 * 10^-5; b = 5.3137 * 10^-4; c = 5.223 * 10^-4

    S/N 1366: a = -5.4385 * 10^-5; b = 6.9345 * 10^-4; c = -2.2 * 10^-3

This is equivalent to a correction of between 0 and -6 m°C in the range 13 - 20 °C for S/N 1322 and -10 - -2 m°C for S/N 1366.

Conductivity

A least squares fit was used to calibrate the CTD conductivity readings to the salinometer data acquired from the water bottle samples:

CR(corrected) = CR(ctd)[A*T(corrected) + b*(P(corrected) + c]

where: CR(ctd) = Conductivity ratio from the CTD

CR(corrected) = Corrected conductivity ratio

    S/N 1322: a = -1.8831437 * 10^-5; b = -2.6107679 * 10^-7; c = 1.0002349

    S/N 1366: a = -2.7020413 * 10^-5; b = -8.2163621 * 10^-7; c = 1.0000295

Using these coefficients, the root mean squared difference between the water sample (salinometer) and corrected CTD salinity for S/N 1366 is 0.004 (8 samples) and for S/N 1322 is 0.004 (108 samples). It is assumed that the CTD conductivity is accurate to 0.01 and that the salinometer is accurate to 0.003. Therefore salinity differences to the magnitude of 0.013 are acceptable. Following the calibrations, all points are within this range.

Fluorometer - Chlorophyll

A Seapoint Chlorophyll Fluorometer was fitted to the CTD rosette sampler. The instrument was and calibrated by comparing the recorded voltages with the measured chlorophyll in water samples collected by Niskin bottles on the CTD upcast. The following equation was used:

Chlorophyll = a * Fluorometer(volts) + b

    Stations 4, 21, 151, 193-317: a = 0.843; b = -0.083; R² = 0.926; Number of samples = 111

    Stations 36, 54, 60, 72, 74, 90, 92: a = 1.099; b = -0.213; R² = 0.937; Number of samples = 16

    Stations 37-53, 55-59, 61-71, 73, 75-89, 91, 93-100: a = 0.579; b = 0.039; R² = 0.927; Number of samples = 80

    Stations 160-187: a = 0.694; b = -0.029; R² = 0.976; Number of samples = 16

Suspended Load

A Seapoint Turbidity Meter was fitted to the CTD rosette sampler and used to estimate the suspended load concentrations. The sensor was calibrated by comparing the recorded voltages with measured suspended load concentrations collected on the CTD upcast:

Suspended Load = a * Turbidity(volts) + b

    All stations: a = 3.0883; b = 0.365; R² = 0.9861; Number of samples = 8

The sensor only logged correctly at stations 2 to 21. A problem with the extra channel circuitry of CTD S/N 1322 appears to have prevented the sensor records from being logged correctly at the other stations.

Photosynthetically Active Radiation

The LICOR light sensor used to measure photosynthetically active radiation was calibrated during January 2002 using a standard lamp. This gave an in-air current equivalent to 0.3495 micromoles m^-2 s^-1 nanoAmp^-1 in water.

Project Information

No Project Information held for the Series

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: