Metadata Report for BODC Series Reference Number 601311
No Problem Report Found in the Database
Centre for Environment, Fisheries and Aquaculture Science (Cefas) data access conditions
The Centre for Environment, Fisheries and Aquaculture Science (Cefas) is an Executive Agency of the Department of Environment, Food and Rural Affairs (Defra), formerly the Ministry of Agriculture, Fisheries and Food (MAFF). It was also known previously as the Directorate of Fisheries Research (DFR). This data policy refers to data collected by the organisation under all titles.
- These data have no specific confidentiality restrictions for academic users. However data are restricted for commercial requests and clearance must be obtained by BODC from Cefas before they are released.
- 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 acknowledgement.
- The recommended acknowledgement is: "This study uses data from the Centre for Environment, Fisheries and Aquaculture Science (Cefas), provided by the British Oceanographic Data Centre."
Falmouth Scientific Integrated CTD (ICTD) Profiler
The FSI ICTD is designed to collect high precision conductivity, temperature and pressure data with self calibrating electronics. This instrument can support five primary sensors (including up to three temperature sensors) and can be coupled with a water bottle sampler. The ICTD is equipped with a titanium housing rated to 7000 m and has a sampling rate of 32 Hz.
Three temperature sensors are available: primary platinum, redundant platinum and exposed thermistor. Any combination of these can be used in the primary channels. The instrument also has multiple RS-232 serial inputs for a variety of sensors including: ADCP, Benthos PSA-916 Altimeter and WetLabs SAFire. There are an additional eight DC input channels that can support virtually any sensor that has a DC output.
|Sensor||Inductive cell||Platinum thermometer||Precision-machined Silicon|
|Range||0 to 70 mS cm-1||-2 to 35°C||Customer specified|
|Accuracy||±0.002 mS cm-1||0.002°C||±0.01 % full scale|
|Resolution||0.0001 mS cm-1||0.00005°C||0.0004 % full scale|
|Response||5.0 cm at 1 ms-1|| |
150 ms Platinum
20 ms Thermistor*
Further details can be found in the manufacturer's specification sheet.
RV Corystes Cruise 10/95 CTD Data Documentation
Five CTD profiles were obtained using a Falmouth Scientific Instruments ICTD (s/n 1351) during this cruise to the Irish Sea; see Figure 1. Digital electronic reversing thermometers (s/n 789 and 926) were used to compare with temperatures recorded by the CTD at maximum descent and samples were collected for salinity analysis to derive a calibration for the instrument conductivity sensor. A 25cm path length transmissometer was used to measure turbidity and samples were collected for suspended load analysis with which to 'calibrate' this sensor ( a light scattering sensor was also fitted but the data return was poor, users forgot to remove the protective cap at some stations). An altimeter was also used.
With only five stations being worked there was insufficient data to make a meaningful statistical assessment but a comparison between temperatures recorded by the digital reversing thermometers indicate that agreement between the two was within the acceptable thermometer tolerance of 0.005 degC for four out of five occasions.
Samples for salinity analysis on the Laboratory's Guildline ( portable )salinometer were collected at every station. But a fault developed during the analysis which left only five samples to compare with the CTD.
Sensor calibration for the CTD
The pressure sensor was calibrated using a dead-weight tester prior to the cruise on 12/09/1995 with the probe at 12 degC and this was used to correct the recorded CTD pressure P(unc):
P(cor) =P(unc) + dP where dP = 0.2
A check was made on this throughout the cruise by noting the 'offset' when the CTD was on deck.
The temperature sensors were calibrated using PRT's on 12/09/1995 and this was used to correct the two temperature sensors:
i.e T(cor) = T(unc) + dT
where dT = a*T(unc)*T(unc) + b*T(unc) + c
|slow temperature sensor||fast temperature sensor|
The differences between the thermometer and the corrected CTD temperatures at the five stations was within the expected tolerance of 0.008 degC (0.005 degC from thermometers, 0.003 from CTD).
A comparison between the CTD salinity estimates after the pressure and (slow) temperature estimates had been corrected indicated that the CTD was reading too low by 0.007 (mean of five values only, range -0.002 to -0.011). A correction for the conductivity sensor was derived by a least square fit to
CR(cor) = CR(ctd) [a*T(cor) + b*P(cor) + c]
where T(cor) and P(cor) are the corrected CTD temperature and pressure and
a = -3.1543008e-5, b = -6.3393695e-7, c = 1.0002841
Using these coefficients the rms difference between water sample and corrected CTD salinity was 0.003 for the five samples.
Fourteen suspended load measurements were used to calibrate the transmissometer estimates logged in the ctd files:
suspended load (mg/l) = a*loge(%trans) + b
where a = -2.42, b = 11.42
General Data Screening carried out by BODC
BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.
Header information is inspected for:
- Irregularities such as unfeasible values
- Inconsistencies between related information, for example:
- Times for instrument deployment and for start/end of data series
- Length of record and the number of data cycles/cycle interval
- Parameters expected and the parameters actually present in the data cycles
- Originator's comments on meter/mooring performance and data quality
Documents are written by BODC highlighting irregularities which cannot be resolved.
Data cycles are inspected using time or depth series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value; the data values will not be altered.
The following types of irregularity, each relying on visual detection in the plot, are amongst those which may be flagged as suspect:
- Spurious data at the start or end of the record.
- Obvious spikes occurring in periods free from meteorological disturbance.
- A sequence of constant values in consecutive data cycles.
If a large percentage of the data is affected by irregularities then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.
Inconsistencies between the characteristics of the data set and those of its neighbours are sought and, where necessary, documented. This covers inconsistencies such as the following:
- Maximum and minimum values of parameters (spikes excluded).
- The occurrence of meteorological events.
This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.
No Project Information held for the Series
|Principal Scientist(s)||Juan Brown (Ministry of Agriculture, Fisheries and Food Lowestoft Fisheries 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|