Metadata Report for BODC Series Reference Number 595740

• 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

The chlorophyll concentration channel is very noisy.

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

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)

RV Corystes Cruise 07/00 CTD Data Documentation

This cruise used the FSI CTD s/n 1322, for 31 stations. Several extra sensors were used during the cruise, and next is a list of those attached and status of results for each station:-

Nutrients and suspended load were collected during the cruise.

STATIONS 3 - 188

(1) Thermometer data

Electronic thermometers were used on 27 occasions. The differences between pairs of thermometers were

(2) Salinity data

Duplicate water samples were collected twice , and both pairs of results were the same.

(3) Sensor calibration for CTD

ALL STATIONS

(a) Pressure

The following calibration, obtained by using a mean of the on deck CTD readings of pressure taken during the cruise, was used to correct the pressure sensor

P (cor) = P (unc) - 0.8

(b)Temperature

Fig.1 shows the difference between the mean thermometer and uncorrected CTD temperature on occasions. The mean difference was -0.011.

Fig.2 shows the differences after the CTD temperatures have been corrected using the following PRT calibration coefficients. The mean difference on 27 occasions was -0.010. This is a larger then usual difference between thermometers and corrected CTD temperatures, and in future different thermometers will be used as a check.

The PRT temperature sensor was calibrated using the laboratory calibration coefficients from 12/5/2000

Tprt(cor) = 0.00001071*T*T + 0.00004531*T - 0.00219633

The fast thermistor temperature sensor was calibrated using the laboratory calibration coefficients from 12/5/2000

Tth(cor) = 0.00001072*T*T - 0.00035499*T + 0.00521577

(c) Salinity

Fig. 3 shows the difference between the water sample salinity as measured with the salinometer and that derived from the CTD , before any calibrations have been applied to the latter's sensors. One CTD salinity was deleted at station 181 (at 5m), as it disagrees with the water sample value, possibly due to CTD travelling up towards the water surface then back down 1m. The mean salinity difference was -0.008 for 74 values.

Fig. 4 shows the ratio of CTD:water sample conductivity ratio after the CTD pressure and temperature sensors have been corrected using the previous coefficients. A set of coefficients have been derived to calibrate the CTD conductivity sensor, using a least square fit between the ratio of water sample and CTD conductivity and the CTD temperature and pressure.

CR (cor) = CR (ctd)*[a*T(cor) + b*P(cor) + c]

where a = -0.249495812e-04, b = 0.194671686e-06, c = 1.00004818

rms salinity difference between water sample and corrected CTD is 0.002 for 72 data values.

Figs. 5 (a), (b), show how effectively the CTD conductivity and derived salinity has been corrected.

The histograms in fig.6 show how well the CTD conductivity is corrected since the upper frame has been derived after the CTD temperature and pressure have been corrected, but before the CTD conductivity calibration has been applied.

If it is assumed that the salinometer is accurate to 0.006 and the CTD salinity to 0.01, then differences upto 0.016 are acceptable, and 100 % are within this when the calibration is applied.

(d) Fluorometer

Stations 3 and 4 only

Dr Haart sensor 5120 was used.

The data are very variable and should only be used with caution.

linear regression calibration coefficients for

CHL = a* FLUOR.VOLTS + b

where a= 1.0461 b= 0.198 r**2 = 0.9195 N = 4

Stations 127 to 185

SPNT fluorometer used (previous stations had wrong lead connections)

a= 2.7069 b= 0.1325 r**2 = 0.762 N = 14

Stations 186 to 188

SPNT fluorometer used

a= 20.109 b= -0.6887 r**2 = 0.8815 N = 6

(e) Suspended Load

Transmissometer 003 was used from station 28 to 188, however the data obtained appear suspect and were not used. The LSS 243 was also used from station 4 to 63, but a wrong lead connection means the data were unusable. The LSS 243 was also used with the correct lead for stations 182 to 188. The data were very variable throughout the cruise and should only be used with caution. The reason for this fluctuation is not known.

the linear regression calibration coefficients were calculated using

SLOAD = a * LSS volts + b

Where:- Stations 182-188

a = 2.5266 b = 0.1168 r**2 = 0.9922 N = 13

(F) Radi

The calibration for this cruise, (from 26/5/99 for sensor 5672), was an in-water coefficient of 0.3469 umol m-2 s-1.

Sue Norris
19/07/2000

General Data Screening carried out by BODC

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

• Irregularities such as unfeasible values
• Inconsistencies between related information, for example:
  • Times for instrument deployment and for start/end of data series
  • Length of record and the number of data cycles/cycle interval
  • Parameters expected and the parameters actually present in the data cycles
• Originator's comments on meter/mooring performance and data quality

Documents are written by BODC highlighting irregularities which cannot be resolved.

Data cycles are inspected using time or depth series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value; the data values will not be altered.

The following types of irregularity, each relying on visual detection in the plot, are amongst those which may be flagged as suspect:

• Spurious data at the start or end of the record.
• Obvious spikes occurring in periods free from meteorological disturbance.
• A sequence of constant values in consecutive data cycles.

If a large percentage of the data is affected by irregularities then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought and, where necessary, documented. This covers inconsistencies such as the following:

• Maximum and minimum values of parameters (spikes excluded).
• The occurrence of meteorological events.

This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.

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: