Metadata Report for BODC Series Reference Number 95550
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Open Data supplied by Natural Environment Research Council (NERC)
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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 9/78 CTD Data Documentation
Documentation for the CTD data collected on RRS Challenger Cruise 9/78 (June 1978) by the Scottish Marine Biological Association, Oban, Argyll, Scotland, UK, under the direction of D. J. Ellett.
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.
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.
The manufacturer's calibration was used to convert the raw data to physical units using the equation below:
Temperature (°C) = (106 /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 (mmho/cm) = (106 /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.
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 = (106 /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 |
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.
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.
No Project Information held for the Series
|Principal Scientist(s)||David J Ellett (Scottish Marine Biological Association)|
Complete Cruise Metadata Report is available here
No Fixed Station Information held for the Series
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|<||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.)|
|E||End of CTD Down/Up Cast|
|G||Non-taxonomic biological characteristic uncertainty|
|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|
|O||Improbable value - user quality control|
|0||no quality control|
|2||probably good value|
|3||probably bad value|
|6||value below detection|
|7||value in excess|
|A||value phenomenon uncertain|
|Q||value below limit of quantification|