Metadata Report for BODC Series Reference Number 341217


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Guildline Model 8705 Digital CTD  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
Project(s) -
 

Data Identifiers

Originator's Identifier CO3B/92/11
BODC Series Reference 341217
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1992-03-03 13:40
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 1.0 decibars
 

Spatial Co-ordinates

Latitude 54.55100 N ( 54° 33.1' N )
Longitude 3.62230 W ( 3° 37.3' W )
Positional Uncertainty Unspecified
Minimum Sensor Depth 1.0 m
Maximum Sensor Depth 11.9 m
Minimum Sensor Height 4.1 m
Maximum Sensor Height 15.0 m
Sea Floor Depth 16.0 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
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
PSALPR01 1 Dimensionless P_sal Practical salinity of the water body by conductivity cell and computation using UNESCO 1983 algorithm
TEMPST01 1 Degrees Celsius WC_temp_CTD Temperature of the water body by CTD or STD
 

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.


Narrative Documents

Guildline 8705 CTD

The 8705 CTD is a conductivity-temperature-pressure profiler designed for marine applications down to depths of 6000 m. The instrument includes an anodised aluminium tube with a steel cage to protect the temperature and conductivity sensors and a urethane cap to protect the pressure sensor.

Specifications

Parameter Range Accuracy Resolution Stability Response time
Pressure 0 to 6000 dbar ± 0.15% of full range ± 0.01% of full range - < 50 ms
Temperature -2 to 30 °C ± 0.005 °C ± 0.0005 °C

± 0.002 °C over 30 days

± 0.0025°C over 6 months

< 50 ms
Conductivity * 100 ppm to 40 ppt ± 0.005 ppt ± 0.001 ppt ± 0.002 ppt over 6 months < 50 ms

* Conductivity specifications are given in terms of equivalent salinity

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

RV Corystes Cruise 3B/92 CTD Data Documentation

Instrumentation

The CTD used was S/N 45056.

Sampling Protocol

50 CTD profiles were obtained during the cruise. Three stations, 12, 15 and 32, had the bung in the CTD cell and therefore the salinity was U/S and set to -9.0 in these profiles. Reversing thermometers were fitted to the Niskin used to collect samples from close to the seabed. Samples for salinity analysis were collected from both near the surface and close to the seabed.

Calibrations

Not all the calibration data collected were used to calibrate the CTD sensors for the following reasons:

  1. Thermometer differences too large (>0.03).

  2. It was clear from the profiles obtained at the time of station that some T and/or S values measured by the CTD were variable, believed real, not an instrument malfunction, and unsuitable for calibration use.

Pressure

The pressure sensor was corrected using the laboratory calibration of 25/03/1992 at T = 6 °C.

P(cor) = P(ctd) - 1.6

A check of comparing CTD pressure with that derived from water depth and altimeter height showed good agreement.

Temperature

The temperature sensor was corrected using the laboratory calibration of 24/03/1992.

T(cor) = T(ctd) + 0.011

One temperature difference between thermometer and uncorrected CTD temperature was untypically high and therefore not used. A comparison between thermometer and uncorrected CTD temperatures is shown in Fig. 1. The uncorrected CTD temperature is likely to be in error by 0.01 (from the laboratory calibration, suggesting a shift of 9 m °C since cruise 1/92) and removing temperature differences between thermometers and uncorrected CTD of 0.03 °C is not entirely justified; 0.04 is probably acceptable (0.02 from the "uncertainty" of the thermometers, 0.01 from CTD and 0.01 which the laboratory calibration tells us to expect).

Salinity

40 salinity samples were used to calibrate the conductivity sensor. Seven pairs of salinity samples showed a larger salinity value than the rest of the data and were deleted before obtaining the conductivity ratio calibration. All the remaining calibration samples have a difference between water sample and corrected CTD salinity of < = 0.01, which is well within the permitted difference of < = 0.016. The calibration derived was:

CRFACT = a*T(ctd) + b*P(ctd) + c

and

CR(cor) = CR(ctd) * CRFACT * CELLFACTOR

where:

a = 0.684543828e-03
b = 0.202726470e-04
c = 0.995339800e+00
CELLFACTOR = 1.0

The rms difference between salinometer and corrected CTD salinity was 0.004.

Fig. 2 shows how effective these coefficients are in correcting the CTD salinity estimates for the calibration samples.

Fig. 3 displays the spread in the ratio of conductivity-ratio of the CTD to that of the water samples prior to applying the correction.

Fig. 4 shows the difference between water sample salinity and the uncorrected CTD equivalent.

Fig. 5 shows the difference between water sample salinity and the corrected CTD equivalent.

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:

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:

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:

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 COR3B/92
Departure Date 1992-02-28
Arrival Date 1992-03-07
Principal Scientist(s)Jonathon Mark Rees (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