Metadata Report for BODC Series Reference Number 93346


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 Scottish Marine Biological Association (now Scottish Association for Marine Science)
Processing Status banked
Project(s) -
 

Data Identifiers

Originator's Identifier C278/113
BODC Series Reference 93346
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1978-02-12 07:48
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval -
 

Spatial Co-ordinates

Latitude 56.80830 N ( 56° 48.5' N )
Longitude 5.95160 W ( 5° 57.1' W )
Positional Uncertainty Unspecified
Minimum Sensor Depth 4.86 m
Maximum Sensor Depth 52.21 m
Minimum Sensor Height 10.79 m
Maximum Sensor Height 58.14 m
Sea Floor Depth 63.0 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

Inspection of the pressure records from this cruise revealed several negative values (by up to 3 dB) at the start of some profiles. Reasonable temperature and salinity values accompanied the negative pressures, which casts some doubt on the accuracy of the pressure calibration. The affected data values have been flagged as suspect.


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 2/78 CTD Data Documentation

Introduction

Documentation for the CTD data collected on RRS Challenger Cruise 2/78 (February 1978) by the Scottish Marine Biological Association, Oban, Argyll, Scotland, UK, under the direction of D. J. Ellett.

Caution

Inspection of the pressure records from this cruise reveals several negative values (by up to 3db) at the start of some records, (while the temperature and salinity values appear reasonable), thus casting some doubt on the accuracy of the pressure calibration. These data values have been flagged.

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.

Calibration

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 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 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) Standard
Deviation
Temperature (°C) 1.0018 0.0258 0.007
Conductivity (mmho/cm) 0.9950 0.1744 0.010
Pressure (dbar) 1.0059 -5.6981 1.362

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.

References

Sharples, F. (1987).
A new data bank of SMBA STD/CTD observations in the Rockall Trough 1975-84. SMBA Marine Physics Group Report No. 36.

Graham, J.M., Sharples, F., Meldrum, D.T. and Edwards, A. (1987).
STD observations in the Rockall Trough 1975-77. SMBA Marine Physics Group Report No. 39.

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 CH2/78
Departure Date 1978-01-30
Arrival Date 1978-02-13
Principal Scientist(s)David J Ellett (Scottish Marine Biological Association)
Ship RRS Challenger

Complete Cruise Metadata Report is available here


Fixed Station Information

Fixed Station Information

Station NameDML Line HD
CategoryOffshore route/traverse

DML Line HD

Line HD is a survey section crossing the Sea of the Hebrides, between Loch Boisdale (South Uist, Scotland) and Loch Moidart on the west coast of Scotland (to the south east of the Isles of Eigg and Muck). The line comprises nine 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 in the mid 1970s to early 1990s.

Line HD has also occasionally been referred to as Line DN.

Nominal station details

DML Line HD: Loch Boisdale (South Uist, Scotland) - Loch Moidart (mainland Scotland)

Station Nominal latitude Nominal longitude Approx.
depth (m)
Comment
HD1 57° 08.3' N 07° 11.0' W 106 Near Loch Boisdale
HD2 57° 05.3' N 07° 00.5' W 135  
HD3 57° 02.3' N 06° 50.0' W 100  
HD4 56° 59.0' N 06° 38.0' W 110 South of Canna
HD5 56° 56.5' N 06° 29.2' W 80  
HD6 56° 54.0' N 06° 21.0' W 84 Sound of Rhum
HD7 56° 51.5' N 06° 12.2' W 55 South of Eigg
HD8 56° 49.5' N 06° 05.0' W 88  
HD9 56° 48.0' N 05° 56.0' W 62 Near Loch Moidart

Other Series linked to this Fixed Station for this cruise - 93254 93266 93278 93291 93309 93310 93322 93334

Other Cruises linked to this Fixed Station (with the number of series) - CH10/81 (1) CH14 (9) CH2/84 (9) CH22 (9) CH4/85 (8) CH6/78 (7) CH6A/81 (7) CH71A (10) CH8/76 (3) CH8/85 (6) CH89B (3) CH9 (4) CH9/78 (7) FR18/87 (9) LF2/89 (9) S5/79 (2)

Fixed Station Information

Station NameDML Line HD Station HD9
CategoryOffshore location
Latitude56° 48.00' N
Longitude5° 56.00' W
Water depth below MSL62.0 m

DML Station HD9

Station HD9 is one of nine fixed STD/CTD stations crossing the Sea of the Hebrides, between South Uist and the west coast of Scotland. The station was established by scientists at Dunstaffnage Marine Laboratory (DML).

Other Cruises linked to this Fixed Station (with the number of series) - CH14 (1) CH2/84 (1) CH22 (1) CH4/85 (1) CH6/78 (1) CH6A/81 (1) CH71A (1) CH8/76 (1) FR18/87 (1) LF2/89 (1)

Fixed Station Information

Station NameDML Sea of the Hebrides STD/CTD Sections
CategoryOffshore area
Latitude56° 57.39' N
Longitude6° 47.91' W
Water depth below MSL

DML Sea of the Hebrides STD/CTD Sections

The Sea of the Hebrides lies between the southernmost islands of the Outer Hebrides and, to the east, the northern Inner Hebridean islands and Scottish mainland. This area of the shelf has been surveyed since the mid 1970s by numerous research and government institutes. The region contains many repeated hydrographic stations, which collectively form transects. These repeated survey transects form part of a greater network of similar sections on the western Scottish continental shelf, which were established by Dunstaffnage Marine Laboratory (DML).

Map of standard Sea of the Hebrides STD/CTD Stations

BODC image

Map produced using the GEBCO Digital Atlas.

The triangles and squares indicate the nominal positions of individual Line HD and HE stations respectively. Measurements made at repeated Sea of the Hebrides STD/CTD stations lie within a box bounded by co-ordinates 56.6° N, 7.664° W at the south west corner and 57.313° N, 5.933° W at the north east corner.

Several repeated hydrographic stations on the Ellett Line/Extended Ellett Line occupy the southern area of the Sea of the Hebrides. Further information about these survey transects are summarised here.

Nominal station details:

DML Line HD: Loch Boisdale (South Uist, Scotland) - Loch Moidart (mainland Scotland)

DML Line HE: Loch Bracadale (Skye, Scotland) - north west of Canna (Scotland)

Other Series linked to this Fixed Station for this cruise - 93254 93266 93278 93291 93309 93310 93322 93334

Other Cruises linked to this Fixed Station (with the number of series) - CH10/81 (7) CH14 (14) CH2/84 (9) CH22 (14) CH4/85 (13) CH6/78 (10) CH6A/81 (12) CH71A (15) CH8/76 (3) CH8/85 (6) CH89B (8) CH9 (4) CH9/78 (9) FR18/87 (14) LF2/89 (14) S5/79 (7)


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