Metadata Report for BODC Series Reference Number 54673
No Problem Report Found in the Database
Public domain data
These data have no specific confidentiality restrictions for users. However, 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 acknowledgment.
The recommended acknowledgment is
"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."
Neil Brown MK3 CTD
The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.
The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.
Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.
These specification apply to the MK3C version.
3200 m (optional)
|-3 to 32°C||1 to 6.5 S cm-1|
0.03% FS < 1 msec
0.003°C < 30 msec
0.0001 S cm-1
0.0003 S cm-1 < 30 msec
Further details can be found in the specification sheet.
RRS Discovery Cruise 81 CTD Data Documentation
This document covers the CTD data collected on RRS Discovery Cruise 81 (January - March 1977) by the Institute of Oceanographic Sciences (Deacon Laboratory) Godalming, Surrey, UK, under the direction of P. M. Saunders.
The instrument used was a Neil Brown Instrument Systems CTD, which measured pressure, temperature and conductivity. The CTD was used alongside a General Oceanics Rosette Multisampler with 12 Niskin bottles and a 10kHz pinger.
Lowering and retrieval rates of 0.5 to 1.0 m/s were employed and the sensors were flushed with distilled water on recovery. Bottle samples and reversing thermometer measurements were made on descent and the sea water samples were analysed using a Guildline Autolab salinometer. Reversing thermometers were calibrated before and after the cruise.
Early in the cruise a pressure electronics board had to be replaced due to a malfunction. This introduced a change in the calibration of the pressure measurement, the nominal value reading low by 2-3 per cent (or 25db at 4000db). In-situ calibration was possible by comparison between the CTD and the pressure determined from pairs of reversing thermometers.
After correction by the amount indicated above, the difference between the CTD and thermometers was computed. Random rms differences of about ±5db were found along with smaller systematic errors produced by the temperature dependence of the sensor (1db per °C for this sensor).
A plot of the difference between CTD temperatures and reversing thermometer values showed a difference of approximately 0.015 °C near 15 °C and 0.030 °C near 30 °C (CTD colder).
The calibration used was:
T = 0.030 + 0.0004995 * RAWTEMP.
No drift was discernable between the first and last stations and in the deep water rms differences are close to ±0.005 °C, the reading error of the thermometer.
From the salinity of the sample and from the corrected temperature and pressure of the CTD the in-situ conductivity was determined. The ratio of sample conductivity (Cs) to CTD conductivity (C) was plotted against pressure. The data fell into 3 groups and within each group of stations the conductivity ratio was a function of temperature and pressure so that:
Cs/C = CCR (1 + aT + bp).
A least squares determination of those quantities yielded:
a = -5.0E-05 per °C
b = -7.0E-08 per db
CCR1 = 1.00094
CCR2 = 1.00105
CCR3 = 1.00109
From the raw conductivity corrected by the factor CCR(1 + aT + bp) the CTD salinity was computed and the difference between it and the sample salinity determined. The rms difference was a function of pressure, about ±0.005ppt in the upper 1000db decreasing to ±0.002ppt in the deep water: the latter figure is close to the accuracy of the Autosal salinometer, the former reflects the variability resulting from heaving the instrument in a gradient.
Calibration groups were as follows:
Group 1 - CCR1 CTD Stations 9291,9329,9331,9333,9336,9338,9340,9342-9346
Group 2 - CCR2 CTD Stations 9368,9371,9374,9377,9380,9382-9387
Group 3 - CCR3 CTD Stations 9388-9398, 9400-9406
Original values were averaged over an interval of one second and calibration coefficients and correction factors applied. A time constant correction algorithm was employed to compensate for the slower response of the platinum resistance thermometer in relation to the other sensors.
Differences between successive values of each parameter were examined; the mean difference and its standard deviation calculated and values greater than several standard deviations from the mean difference were checked. Genuinely suspect data were then replaced by interpolated values.
Derived quantities were computed from algorithms published by Fofonoff et al (1974). To remove the effect of ships heave data cycles were sorted by pressure before all values were averaged at 10db intervals, centred on 5db, 15db and so forth
Saunders, P.M. 1980.
CTD data obtained during Discovery Cruise 81. IOS Data Report No. 17. Unpublished manuscript.
Fofonoff, N.P., Hayes, S.P. and Millard Jr., R.C. 1974.
WHOI/Brown CTD microprofiler: methods of calibration and data handling. Woods Hole Oceanographic Institution WHOI-74-89.
No Project Information held for the Series
|Principal Scientist(s)||John C Swallow (Institute of Oceanographic Sciences Wormley Laboratory), W John Gould (Institute of Oceanographic Sciences Wormley Laboratory)|
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|