Metadata Report for BODC Series Reference Number 474248
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
RRS Charles Darwin CD51 CTD transmissometer data quality report
Transmittance - TVLTPR01
Although the originator suggested units were converted from raw in the cruise report, the actual values suggest they are in units of volts and therefore have been assigned the TVLTPR01 code. Data should be used with caution.
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
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.
Specifications
These specification apply to the MK3C version.
| Pressure | Temperature | Conductivity | |
| Range | 6500 m 3200 m (optional) | -3 to 32°C | 1 to 6.5 S cm-1 |
| Accuracy | 0.0015% FS 0.03% FS < 1 msec | 0.0005°C 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.
SeaTech Transmissometer
Introduction
The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.
Specifications
- Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).
- Beam diameter: 15 mm
- Transmitted beam collimation: <3 milliradians
- Receiver acceptance angle (in water): <18 milliradians
- Light source wavelength: usually (but not exclusively) 660 nm (red light)
Notes
The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.
A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.
Further details can be found in the manufacturer's Manual.
RRS Charles Darwin CD51 CTD data processing
Originator processing
18 full depth casts were performed on cruise CD51 using the IOSDL (Institute of Oceanographic Sciences Deacon Laboratory) Deep CTD 01 mounted in the 24 x 10 litre General Oceanics rosette multisampler frame. A Seatech 1 metre transmissometer and an IOSDL pinger were also mounted on the frame. Three SIS digital reversing thermometers and two SIS reversing pressure meters were used on two thermometer frames to obtain calibration information. Unfortunately on the 5th station, the CTD was briefly placed on the seabed and toppled over damaging 3 Niskin bottles.
The performance of the CTD, multisampler etc and new deck equipment was good throughout the cruise. From salinity samples measured on the Autosal, the conductivity cell correction ratio remained stable throughout.
All data were logged through the RVS level A, B and C system and backed up onto the PS2 tape streamer and copied into Pstar format on the SUN. It was then processed in a standard manner with a series of command files. Information such as the position, time and bottom depth of the CTD were added to the header of each CTD file, and simple automatic editing performed before the data were calibrated, converting raw to physical units. The data were then averaged to 2db intervals.
Calibration coefficients were initially taken to be the values determined in the laboratory. The temperature sensor time constant and the conductivity-ratio factor were both adjusted to improve the data quality. The latter was determined by comparing the CTD salinity with salinity measured from bottle samples. The temperature time constant was estimated by minimising salinity spikes in strong temperature gradients.
Reference
Griffiths, G et al. (1990) RRS Charles Darwin Cruise 51 24Jul-21Aug 1990. Temperature salinity and velocity structure of the Iceland Faeroes Front and North Atlantic Water inflow to the GIN Sea. Institute of Oceanographic Sciences Deacon Laboratory, Cruise Report, No. 216, 42pp.
BODC processing
The data arrived at BODC in one Pstar format file per cast. These files were reformatted to the BODC internal netCDF subset, QXF. The following table shows how the variables within the Pstar files were mapped to the appropriate BODC parameter codes:
| Originator's Parameter Name | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| press | dbar | Pressure corrected against deck readings | PRESPR01 | dbar | |
| temp | °C | Calibrated temperature | TEMPST01 | °C | |
| salin | Calibrated salinity | PSALST01 | dimensionless | Salinity calibrated by comparison with bottle samples | |
| potemp | °C | Potential temperature | POTMCV01 | °C | |
| cond | mmho/cm | Conductivity | CNDCST01 | S/m | Conversion applied: /10 |
| oxygen | ml/l | Oxygen concentration | DOXYPR01 | micromol/l | Conversion applied: *44.66 |
| Oxygen saturation | OXYSZZ01 | % | Derived by BODC | ||
| SIGTPR01 | Derived by BODC using PRESPR01, TEMPST01 and PSALST01 | ||||
| trans | - | Transmittance | TVLTPR01 | volts | Although the originator suggests units were converted from raw, the values suggest otherwise. Data should be used with caution. |
The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, missing data by both setting the data to an appropriate value and setting the quality control flag.
Project Information
World Ocean Circulation Experiment (WOCE)
The World Ocean Circulation Experiment (WOCE) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.
WOCE had two major goals:
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Goal 1. To develop models to predict climate and to collect the data necessary to test them.
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Goal 2. To determine the representativeness of the Goal 1 observations and to deduce cost effective means of determining long-term changes in ocean circulation.
Data Activity or Cruise Information
Cruise
| Cruise Name | CD51 |
| Departure Date | 1990-07-24 |
| Arrival Date | 1990-08-21 |
| Principal Scientist(s) | Gwyn Griffiths (Institute of Oceanographic Sciences Deacon Laboratory) |
| Ship | RRS Charles Darwin |
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 |
