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Metadata Report for BODC Series Reference Number 603631


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Unknown transmissometer  transmissometers
Falmouth Scientific Instruments Integrated CTD Profiler  CTD; water temperature sensor; salinity sensor
Instrument Mounting research vessel
Originating Country United Kingdom
Originator -
Originating Organization Ministry of Agriculture, Fisheries and Food Lowestoft Fisheries Laboratory (now Centre for Environment, Fisheries and Aquaculture Science Lowestoft Laboratory)
Processing Status banked
Online delivery of data Download available - Ocean Data View (ODV) format
Project(s) -
 

Data Identifiers

Originator's Identifier CO09/96/146
BODC Series Reference 603631
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1996-07-16 21:24
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 1.0 decibars
 

Spatial Co-ordinates

Latitude 54.39120 N ( 54° 23.5' N )
Longitude 4.81220 W ( 4° 48.7' W )
Positional Uncertainty Unspecified
Minimum Sensor or Sampling Depth 4.0 m
Maximum Sensor or Sampling Depth 37.7 m
Minimum Sensor or Sampling Height 3.3 m
Maximum Sensor or Sampling Height 37.0 m
Sea Floor Depth 41.0 m
Sea Floor Depth Source -
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
ATTNMR011per metreAttenuation (red light wavelength) per unit length of the water body by 20 or 25cm path length transmissometer
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
TEMPST011Degrees CelsiusTemperature of the water body by CTD or STD
TSEDTR011Milligrams per litreConcentration 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

Centre for Environment, Fisheries and Aquaculture Science (Cefas) data access conditions

The Centre for Environment, Fisheries and Aquaculture Science (Cefas) is an Executive Agency of the Department of Environment, Food and Rural Affairs (Defra), formerly the Ministry of Agriculture, Fisheries and Food (MAFF). It was also known previously as the Directorate of Fisheries Research (DFR). This data policy refers to data collected by the organisation under all titles.

  • These data have no specific confidentiality restrictions for academic users. However data are restricted for commercial requests and clearance must be obtained by BODC from Cefas before they are released.
  • 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 acknowledgement.
  • The recommended acknowledgement is: "This study uses data from the Centre for Environment, Fisheries and Aquaculture Science (Cefas), provided by the British Oceanographic Data Centre."

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:

Parameter Conductivity Temperature Pressure
Sensor Inductive cell Platinum thermometer Precision-machined Silicon
Range 0 to 70 mS cm-1 -2 to 35°C Customer specified
Accuracy ±0.002 mS cm-1 0.002°C ±0.01 % full scale
Resolution 0.0001 mS cm-1 0.00005°C 0.0004 % full scale
Response 5.0 cm at 1 ms-1

150 ms Platinum

20 ms Thermistor*

25 ms

*Optional

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

RV Corystes Cruise 09/96 CTD Data Documentation

Seventy-six CTD profiles were obtained using a FSI ICTD (s/n 1351) during this cruise to the North Sea and Irish Sea; see Figures 1and 2. Twenty-two profiles were at the same location, stations 77 to 98. Electronic reversing thermometers were used to compare with temperatures recorded by the CTD and samples were collected for salinity analysis to derive a calibration for the conductivity sensor. A 25cm path length transmissometer and an optical back scatter sensor was fitted to the niskin rosette. Samples were collected for suspended load analysis for calibration of these sensors.

Thermometer data

Two pairs of digital reversing thermometers were used during the cruise and satisfactory measurements were made by both on 57 occasions ( thermometers were used only for the near bottom sample). In all instances the difference between them were < 0.005 degC.

Salinity data

Samples for salinity analysis on the Laboratory's Guildline salinometer were collected at every station. Duplicate samples were drawn on seventeen occasions and their differences were as follows:

Difference No. Accumulative %
0.000 6 35
0.001 9 88
0.002 1 94
0.003 0 94
0.004 1 100

CTD Sensor Calibration

(a) Pressure

The pressure sensor was calibrated using a dead-weight tester prior to the cruise on 17/06/1996 with the probe at a temperature of 12 degC. This indicated a correction near 0.3dbar, but the recorded CTD pressure P(unc) has been corrected using the 'on deck' pressure recorded by the sensor immediately before being deployed at each station.

ie P(cor) =P(unc) + dP

where dP = 0.0 dbar at stations 1 to 6, 28th to 29th June

0.6 dbar at stations 13 to 58, 1st to 5th July

0.4 dbar at stations 77 to 98, 9th to 10th July

0.3 dbar at stations 146 to 152, 16th to 17th July

0.5 dbar at stations 171 to 177, 21st to 22nd July

(b) Temperature

Both fast and slow temperature sensors fitted to the CTD were calibrated using PRT's on 17/06/96 and correction factors derived:

T(cor) = T(unc) + dT

dT = aT(unc)T(unc) + bT(unc) + c

where,

slow sensor a=0.0000 b=0.0000 c=-2.000e-3

fast sensor a=4.47249e-5 b=-7.6952e-4 c=-3.385e-3

The fast sensor coefficients are equivalent to corrections of -0.004 to -0.007 degC for temperatures between 4 and 16 degC.

A comparison was made with the temperatures from the slow sensor and reversing thermometers. Figure 3 shows the difference between thermometer and corrected CTD temperatures. A mean difference of -0.004 degC (std dev 0.005, 57 data values) is well within the expected tolerances ( 0.005 degC for the thermometers alone).

(c) Conductivity

The difference between salinometer and CTD salinity before any corrections are applied to the sensors is plotted in Figure 4. The mean difference (-0.001) increases to -0.003 after the pressure and temperature calibrations have been applied, the effect of decreasing the CTD temperature by 0.002 degC.

Figure 5 shows conductivity ratio(CTD): conductivity ratio(water samples), the water sample conductivity ratio being that from the salinometer salinity at the corrected pressure and temperature given by the CTD. The conductivity is over-estimated. To compensate for this a least square fit was used to determine appropriate calibration coefficients:

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

a = 7.2288215e-6, b = -2.815320 e-7, c = 0.9998728

Using these coefficients the rms difference between water sample and corrected CTD salinity is 0.003 for 144 samples. Figures 6 and 7 show how effective these coefficients are correcting the CTD derived salinity. The histograms of Figure 7 show the differences before and after the application of these conductivity coefficients. The upper histogram shows the differences after temperature and pressure have been corrected; the bottom histogram after these and the conductivity calibration have been applied. If it assumed that the CTD is accurate to 0.01 and the salinometer to 0.006 then differences of +/-0.016 are acceptable. In this instance all differences are within 0.009.

Note that at some stations the computed salinity estimates within the thermocline were found to be noisy, presumably a consequence of mis-matched sensor responses. The profiles from the North Sea were especially poor. Some smoothing has been attempted, removing density inversions > 0.02 kg/m, but users of the profiles should be aware that derived salinity at these depths are suspect.

Suspended Load Estimates

Two optical sensors were used to estimate sediment loads in the water column: a transmissometer and a back scatter sensors (LSS).

Each of the sensors were calibrated by comparing recorded voltages with the suspended loads of samples collected during the CTD cast. There was no significant difference between the two alternative calibrations and the CTD profiles have suspended load estimates derived from the transmissometer measurements.

The calibration coefficients for the profiles follow. The stations have been grouped to take into account the geographic area from which profiles were obtained.

suspended load (mg/l) = a*loge(% transmission) + b

Station range a b N R rmse comment
1 to 34, 171 to 177 -5.565 25.687 54 0.61 0.34 North Sea
77 to 98 -7.432 34.065 86 0.96 0.25 Irish Sea, same location
41 to 58, 146 to 152 -7.209 33.124 90 0.85 0.50 Irish Sea

Ken Medler
10 September 1996

BODC image BODC image BODC image BODC image BODC image BODC image BODC image BODC image

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

Cruise Name COR9/96
Departure Date 1996-06-27
Arrival Date 1996-07-24
Principal Scientist(s)Juan Brown (Ministry of Agriculture, Fisheries and Food Lowestoft Fisheries Laboratory)
Ship RV Corystes

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