Metadata Report for BODC Series Reference Number 598725

• 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

In the salinity channel there are large spikes and null values that have been flagged on the thermocline. This could be due to a mismatch between the conductivity cell and the thermistor.

Chlorophyll concentration channel data values are null in all or part of this cast.

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.

Dr Haardt BackScat I fluorometer

The Dr Haardt BackScat I is a backscatter fluorometer designed to detect concentrations of a variety of substances in the water column. The instrument uses a Xe-flashlight source and exhibits a fast response and low power consumption. Integrated turbidity and other sensors are available and the instrument has a titanium housing rated to a maximum depth of 6000 m.

Each fluorometer is custom-built to measure substances of interest. Available spectral ranges are visible, UV I and UV II. A range of filter units are available for the measurement of chlorophyll-a, phycoerythrin, humic acids, aromatic hydrocarbons, phenol, oils, rhodamine B, sulforhodamine, fluorescein, eosin, pyranin and naphthionate.

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 07/97 CTD Data Documentation

Stations 2 - 66

For this cruise the FSI CTD (s/n 1366) was used.

Nineteen CTD profiles were obtained. Water temperatures were measured with two electronic reversing thermometers. Water samples were collected for salinity analysis and measurement of nutrients, chlorophyll and suspended load content.

PART A

1. THERMOMETER DATA

Two electronic reversing thermometer readings were available at 17 stations. Four pair were removed because the differences between them and the CTD were too great. All the differences between the remaining pairs of thermometers were <0.005°C.

2. SALINITY DATA

Water samples were taken at all stations for later analysis. Three pairs of duplicate samples were taken. The differences were 0.003, 0.002 and 0.002 respectively.

3. SENSOR CALIBRATION FOR FSI CTD

a) Pressure

The laboratory calibration of June 1997 was used to correct the pressure sensor:

Pcor = Pctd - 1.0 db

b) Temperature

Fig. 1 shows the differences between the mean thermometer temperatures and uncorrected CTD temperatures. The mean difference for 13 points was 0.007°C. The PRT and thermistor were corrected using the laboratory calibration of June 1997 where:

Tcor = Tctd + dT

when:

dT=ax^2 + bx + c

and for the PRT

a= 0.0000095168, b = -0.0005463732, c = 0.0054077205

and for the thermistor

a= 0.0000897380, b = -0.0026687945, c= 0.0196128684

The CTD temperatures were corrected using the PRT sensor.

Fig. 2 shows the differences between the thermometer readings and CTD temperatures after the latter have been corrected.

c) Salinity

Fig. 3 and Fig. 4 are plots using the water sample salinity values which were derived from analysis done on the Guildline salinometer. This clearly shows that something is wrong, and discussions with KJM have indicated that the problems lies with the water sample salinity values.

Accordingly calibration of the CTD salinity sensor was not possible using these sample results. Consequently the coefficients derived for CORYSTES 9/97 were used since this cruise was only 3 weeks after CORYSTES 7/97.

For the data held on the LSDM the CTD salinity value has been substituted in each case.

The coefficients were derived to calibrate the CTD conductivity sensor using a least square fit between the ratio of water sample conductivity to CTD conductivity and the CTD temperature and pressure.

CR(cor) = CR(ctd)*{a*T(cor) + b*P(cor) + c}

where T(cor) and P(cor) are the corrected CTD temperature and pressure and where:

a = -0.490652762E-04, b = -0.449967172E-06, c = 0.100068654E+01

PART B

1. LSS (volts) AND SUSPENDED LOAD (mg/l)

During the whole of this cruise a light scattering sensor (LSS) was used and recorded voltages were noted at each sampling depth on the log sheet. A linear regression was calculated in the form of

S.Load = bx + c

where b = 6.790 c = 0.578 r = 0.85 N = 31

2. FLUOROMETER AND CHLOROPHYLL (mg/m^3)

A Dr Haardt fluorometer was fitted to the CTD for this cruise. A linear regression was used of the form:

Chl = a*Fv + b where Fv = fluorometer volts

and a = 7.384 b = -0.169

rmse=0.65, r^2=0.7, N=55

S R Jones
November 1997

After the cruise it was found that the fluorometer had not been wired correctly and this results in noisy profiles from this sensor. The *.corchl files include the fluorometer voltage but the chlorophyll has been set to -9.0.

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: