Metadata Report for BODC Series Reference Number 382801


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Bissett-Bermann 9040 CTD system  CTD; water temperature sensor; salinity sensor
Instrument Mounting research vessel
Originating Country United Kingdom
Originator -
Originating Organization Dunstaffnage Marine Laboratory (now Scottish Association for Marine Science)
Processing Status banked
Project(s) -
 

Data Identifiers

Originator's Identifier CH75/91/042
BODC Series Reference 382801
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1991-03-01 21:18
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval -
 

Spatial Co-ordinates

Latitude 55.76670 N ( 55° 46.0' N )
Longitude 7.48170 W ( 7° 28.9' W )
Positional Uncertainty Unspecified
Minimum Sensor Depth 0.2 m
Maximum Sensor Depth 53.21 m
Minimum Sensor Height 6.78 m
Maximum Sensor Height 59.8 m
Sea Floor Depth 60.0 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

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."


Narrative Documents

Bissett-Bermann 9040 Conductivity Temperature and Depth

The basic configuration of the B-B 9040 CTD incorporates pressure, temperature and conductivity sensors which could be logged digitally. This system also made it possible to derive other parameters, such as salinity, depth and sound velocity.

The instrument was versatile and it was possible to attach a dissolved oxygen sensor or to change the CTD housing, allowing it to obtain data from deeper layers in the water column. The accuracy for salinity is ±0.02 ppt , and ±0.02°C for temperature.

This instrument was also known as the Plessey 9040.

RRS Challenger Cruise 75/91 CTD Data Documentation

Introduction

Documentation for the CTD data collected on RRS Challenger 75/91 (February - March 1991) by the Dunstaffnage Marine Laboratory, Oban, Argyll, Scotland, UK, under the direction of D. J. Ellett.

Instrumentation

The instrument used was a Bissett Berman 9040 CTD system and the data were logged on a Hewlett Packard 9820 and stored in an integer format. Instrument lowering and raising speeds were between 0.5m/s and 1m/s. An acoustic pinger was placed above the CTD to give an accurate depth measurement, this could then be used to check the CTD pressure calibration. An NIO bottle with reversing thermometers was placed above the pinger, within 2m of the CTD system. A bottle sample was taken at the bottom of the cast providing the temperature and salinity are uniform at that point. If large temperature or salinity gradients were present then the bottle sample was triggered at a suitable site on the upcast. A surface salinity sample was also taken at the start of the dip.

Calibrations and Data Quality

The CTD was not calibrated in the laboratory. The manufacturer's calibration was used and water samples taken to check the calibration and apply corrections where necessary.

Temperature

The manufacturer's calibration was used to convert the raw data to to physical units using the equation below:

Temperature (°C) = (10**6/Pt -2238.68/55.84)
where Pt is the temperature period in microseconds

These values were then plotted against the water bottle (i.e. reversing thermometer) temperatures and a regression line fitted to the data such that:

Temperature(WB) = m x Temperature(CTD) + c

Then the regression coefficients (m and c) were applied to correct the CTD temperature data - these are given in the table below.

Conductivity

The manufacturer's calibration was used to convert the raw data to to physical units using the equation below:

Conductivity (mmho/cm) = (10**6/Pc - 4995)/58.12 + 10
where Pc is the conductivity period in microseconds

The water bottle salinities and corrected CTD temperatures were used to calculate the water bottle conductivity values. These values were then plotted against the CTD conductivities and a regression line fitted to the data such that:

Conductivity(WB) = m x Conductivity(CTD) + c

Then the regression coefficients were applied to correct the CTD conductivity data - these are given in the table below.

Pressure

The depths from the acoustic pinger were noted where the bottle samples were taken and then used to check the calibration of the pressure sensor - unless calibration values were available from the reversing thermometers. The equation below was used to convert the pressure period to physical units.

Pressure = (10**6/Pd - 9712)/0.26267
where Pd is the pressure period in microseconds

A regression fit was carried out using the calibration values and the slope and intercept determined. The pressure values could then be corrected using:

Pressure (CORR) = m x Pressure(CTD) + c

The fit of the CTD data to the water bottle calibration data is given in the table below:

Variable Slope (m) Intercept (c)
Temperature (°C) 1.0143260 -0.158323
Conductivity (mmho/cm) 1.0130279 -0.362879
Pressure (dbar) 1.0072947 13.508089

Data Processing

Obvious wild points were edited out of the calibration file and the calibration programs run to obtain values for the slopes and intercepts for temperature, pressure and conductivity. These were then applied to the uncalibrated data. Conductivities were converted to conductivity ratios and then converted to salinities using UNESCO recommended routines and sigma-t was calculated. The data values were then sieved to ensure a minimum separation between pressure values of 1 dbar. The data were then visually inspected and major spikes flagged.

Reference

Fofonoff, N.P. and Millard Jr., R.C. (1983).
Algorithms for the computation of fundamental properties of sea water. UNESCO Technical Paper on Marine Science 44.


Project Information


No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Cruise Name CH75B
Departure Date 1991-02-23
Arrival Date 1991-03-03
Principal Scientist(s)David J Ellett (Dunstaffnage Marine Laboratory)
Ship RRS Challenger

Complete Cruise Metadata Report is available here


Fixed Station Information

Fixed Station Information

Station NameDML Line D
CategoryOffshore route/traverse

DML Line D

Line D is a survey section heading due west from Islay off the west coast of Scotland. The line comprises 11 fixed STD/CTD stations, which were established as part of routine monitoring work on the Scottish continental shelf by Dunstaffnage Marine Laboratory (DML). The line was occupied between the mid 1970s and mid 1990s.

Map of standard DML Line D STD/CTD Stations

BODC image

Map produced using the GEBCO Digital Atlas.

The white triangles indicate the nominal positions of each standard station on DML Line D.

Nominal station details

DML Line D: West of Islay, Scotland

Station Nominal latitude Nominal longitude Approx.
depth (m)
Comment
98D * 55° 46.0' N 09° 00.0' W 130  
99D * 55° 46.0' N 08° 30.0' W 115  
0D 55° 46.0' N 08° 00.0' W 105  
1D 55° 46.0' N 07° 41.5' W 85  
2D 55° 46.0' N 07° 29.0' W 60  
3D 55° 46.0' N 07° 16.5' W 60  
4D 55° 46.0' N 07° 04.0' W 50  
5D 55° 46.0' N 06° 55.5' W 50  
6D 55° 46.0' N 06° 46.5' W 45  
7D 55° 46.0' N 06° 37.5' W 60  
8D 55° 46.0' N 06° 30.0' W 30 Machir Bay (Islay)

* Stations 98D and 99D were incorporated into Line D for occupations carried out in 1991 and 1992.

In addition to Line B, there are other DML repeated survey transects which converge at Islay. These are Line B,Line C, andLine P.

Other Series linked to this Fixed Station for this cruise - 382769 382770 382782 382794 382813 382825 382837 382849 382850 382862

Other Cruises linked to this Fixed Station (with the number of series) - CD44 (9) CH1/85 (9) CH10/77 (5) CH10/81 (4) CH11/83 (8) CH112 (9) CH114 (9) CH14 (9) CH2/84 (8) CH22 (9) CH30 (5) CH4/85 (9) CH7A/83 (9) CH8/76 (5) CH8/85 (9) CH86B (9) CH9 (9) CH97 (11) FR13/85 (9) FR13/87 (8) FR14B/87 (8) FR8/86 (9) LF1/89 (9) LF2/89 (9) S5/79 (7)

Fixed Station Information

Station NameDML Line D Station 2D
CategoryOffshore location
Latitude55° 46.00' N
Longitude7° 29.00' W
Water depth below MSL60.0 m

DML Station 2D

Station 2D is one of 11 fixed STD/CTD stations west of Islay (Scotland), established by scientists at Dunstaffnage Marine Laboratory (DML).

Other Cruises linked to this Fixed Station (with the number of series) - CD44 (1) CH1/85 (1) CH10/81 (1) CH11/83 (1) CH112 (1) CH114 (1) CH14 (1) CH2/84 (1) CH22 (1) CH30 (1) CH4/85 (1) CH7A/83 (1) CH8/85 (1) CH86B (1) CH9 (1) CH97 (1) FR13/85 (1) FR13/87 (1) FR14B/87 (1) FR8/86 (2) LF1/89 (1) LF2/89 (1) S5/79 (1)


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