Metadata Report for BODC Series Reference Number 475694
Metadata Summary
Problem Reports
Data Access Policy
Narrative Documents
Project Information
Data Activity or Cruise Information
Fixed Station Information
BODC Quality Flags
SeaDataNet Quality Flags
Metadata Summary
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Problem Reports
No Problem Report Found in the Database
Data Access Policy
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."
Narrative Documents
RRS Discovery 165A CTD Data Documentation
Introduction
This data document covers the CTD data collected during RRS Discovery cruise 165A (26th January to 26th February 1987) under the direction of J. Luyten to the eastern S Atlantic and SW Indian Ocean.
CTD Data Logging and Reduction
Logging, reduction and calibration of the Neil Brown Instrument Systems (NBIS) CTD are fully described by PRS, to which the reader is referred for details. Likewise, further editing of SeaSoar CTD data is described by PRS. Only a brief summary will be given here.
All CTD data are initially logged on an NBIS deck unit, written to a DIGIN format tape for backup, displayed on a BBC microcomputer and transferred to a Level A microcomputer, which edited the 16 hz (8 hz for shallow SeaSoar CTD) data before averaging them to one sample per second. The averaged data were then passed to a PDP11/34 computer for calibration and further processing. This route was used throughout Cruise 165A, with only a very few part casts having to be recovered from backup DIGIN tapes or Level C data. Cruise specific calibration information is described below.
Deep CTD Calibration
Pressure
CTD pressures on Cruise 164 and 165A were checked against a Precision Echo Sounder as described by PRS. The Cruise 165A data were included in that comparison, from which it was concluded that CTD pressures were correct within a few metres. The calibration used was
P(dbar) = 0.1*P(raw) - 12.0
Temperature
The few reversing thermometer values from the ten casts on Cruise 165A gave no grounds for modifying the long term stable laboratory calibration
T(°C) = T(raw)*0.0005*0.9990317 + 0.0258
Salinity
The conductivity cell had fouled three casts before the end of the previous cruise. Using a conductivity ratio of 0.99937 it was concluded that salinities for the last three casts of Cruise 164 were 0.019 too high. After a 16-day break between the last cast of Cruise 164 and the first of Cruise 165A, it was not too surprising that the salinity corrections had changed from -0.019 to about 0.007. Statistics for the 6 levels at which samples were drawn for casts 11462-71 are given in Table 1. Differences between mean bottle and CTD salinities range from 0.008 to -0.002, with some hint of a trend with depth or salinity (Table 1a, right hand column). A simple way to reduce this possible 0.010 salinity trend was to recalibrate salinity as shown in Table 1b, which was done.
Oxygen
The oxygen sensor drifted less during Cruise 165A than it had on Cruise 164, and it was on occasion possible to fit values of C, ALPHA and BETA in the equation
0(cal)(m/l) = C*0(RAW)*EXP(ALPHA*T(L) + BETA*P)*0(sal)(T,S)
to calibration values from several casts at once (Table 2). T(L) was taken, as before, to be the unlagged CTD temperature. From the standard deviations of bottle minus CTD differences, we estimate the oxygens to be correct within 0.2 ml/l, the quoted error of the Beckman oxygen sensor.
Table 1a. Salinity calibrations on Cruise 165A
Position in Water Column | No. in Sample | S(B)-S(CTD) Mean | S(B)-S(CTD) Std.Dev. | S(CTD) Mean | S(CTD) Std.Dev. |
---|---|---|---|---|---|
Surface | 9 | -0.002 | 0.003 | 35.570 | 0.079 |
Thermocline | 9 | 0.003 | 0.004 | 35.017 | 0.185 |
Oxygen Maximum | 10 | 0.007 | 0.005 | ||
Oxygen Minimum | 10 | 0.008 | 0.006 | ||
3000 dbar | 8 | 0.007 | 0.003 | ||
Bottom | 10 | 0.003 | 0.003 | ||
Bottom 4 levels | 38 | 0.006 | 0.005 | 34.642 | 0.160 |
Table 1b. Comparison of corrected salinities
S(CORR) = 0.9909095*S(CTD) + 0.3213
S(CTD) | S(COR) |
---|---|
35.570 | 35.568 |
35.017 | 35.020 |
34.642 | 34.648 |
Table 2. Oxygen calibration constants on Cruise 165A
Cast 114-- | C*10(3) | ALPHA (°C(-1)) | BETA*10(3) (DBAR(-1)) | No. in sample | Std.Dev. of 0(B)-0(CTD)(ml/l) |
---|---|---|---|---|---|
62 | 1.398 | -0.0322 | 0.143 | 6 | 0.06 |
65 | 1.551 | -0.0343 | 0.126 | 6 | 0.22 |
63-66 | 1.471 | -0.0344 | 0.135 | 24 | 0.20 |
67-71 | 1.331 | -0.343 | 0.133 | 29 | 0.24 |
Project Information
No Project Information held for the Series
Data Activity or Cruise Information
Cruise
Cruise Name | D165A |
Departure Date | 1987-01-26 |
Arrival Date | 1987-02-26 |
Principal Scientist(s) | James R Luyten (Woods Hole Oceanographic Institution Department of Physical Oceanography) |
Ship | RRS Discovery |
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 |
B | nominal value |
Q | value below limit of quantification |