Metadata Report for BODC Series Reference Number 551724

• 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

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

Falmouth Scientific NXIC CTD Series

The FSI NXIC CTD Series is a collection of rugged Conductivity-Temperature-Depth profilers that utilise the patented Non-eXternal Inductive Cell (NXIC) conductivity sensor, which was originally developed for the US Navy DT-705 Sound Velocity/Salinity sensor. The CTDs are fast sampling, fully integrated instruments with optional battery power, datalogging and external analog sensor input.

Models in the collection include the NXIC CT Bio Direct Read-500M, NXIC CTD Bio Direct Read-500M, NXIC CTD Bio Auto-500M, NXIC CTD Direct Read-500M, NXIC CTD Direct Read-700M, NXIC CTD Auto-500M, NXIC CTD Auto-700M, NXIC CTD-ADC with external sensors, and the NXIC ETSG Thermosalinograph. Parameters are measured to an accuracy ranging from 0.002-0.010 mS/cm for conductivity, 0.005 degC for temperature and 0.08% for full scale pressure. Now marketed by Teledyne RD Instruments.

Specifications

Further details can be found in the manufacturer's specification sheet and Series Brochure.

RV Cirolana 9B/1993 (JONUS Exercise 20) CTD Data Documentation

Introduction

This cruise used the FSI CTD s/n 1322 at all 62 CTD stations. The logger failed during one (station 161) so only 61 profiles are available.

Data Collection

Reversing thermometers were used to measure water temperature and samples were collected for salinity analysis using the recently acquired portable salinometer.

Left and right thermometer temperatures were available on 51 occasions, but one pair was subsequently rejected because both had been influenced by direct sunshine. Note that temperature differences are not available for all stations because it was seen that water temperatures were varying over the four minutes allowed for acclimatisation; thermometers were not read in these circumstances.

All thermometers were graduated at 0.02 °C intervals and a comparison of the differences is as follows:

Thus, 98% of the differences lie within the range ± 0.02 °C, the thermometer scale graduation.

Duplicate water samples were collected on 21 occasions for analysis with a portable salinometer. The distribution of the differences is as follows:

Sensor Calibration for FSI CTD

Pressure

A laboratory calibration during October 1993, albeit at room temperature, suggested that no correction to the recorded CTD pressure was required,

i.e. P(cor) = P(ctd)

Temperature

Fig. 1 shows the differences between the (mean) thermometer and uncorrected CTD temperature. The mean of the 50 differences is - 0.005 °C.

This is an excellent agreement with the laboratory post-cruise calibration of 13 October, which estimated the CTD correction to be -0.004 °C.

The sensor was therefore corrected using the laboratory calibration coefficients:

T(cor) = T(ctd) + dT

where dT = -0.004

The differences between thermometer and CTD temperatures after the latter have been corrected is shown in Fig. 2. The mean difference is -0.001 °C and all differences lie well within ±0.03 °C, supporting the belief that if the thermometers are accurate to ± 0.02 °C then the CTD temperatures are accurate to ±0.01 °C. In fact, all differences are within ±0.015 °C suggesting that the above tolerances may be over- estimated.

Salinity

Fig. 3 shows the difference between the water sample salinity as measured with the salinometer and that derived from the CTD before any calibrations have been applied to the latter's sensors. Note that a few data values have been removed prior to plotting Fig. 3 because they were not suitable for determining calibration coefficients:

1. Stations 202 to 232 were from the Bull Anchorage in the River Humber, whilst Cirolana was anchored. Throughout the JONUS exercise it has been found that the CTD salinity estimates from estuaries are suspect, perhaps because of high sediment loads influencing the instrument conductivity measurement, and CTD data from these stations have not been used;
2. The conductivity recorded by the CTD at station 178 was variable during the time that the calibration sample was collected and the CTD data have not been used.

Fig. 3 suggests that the CTD has a tendency to over-estimate salinity by 0.007 (standard dev. 0.005: 89 data values).

Fig. 4 shows the difference between salinometer and CTD salinity after the temperature and pressure sensors have been corrected. The `offset' has increased to 0.010 (standard deviation 0.005: 89 data values).

Fig. 5 shows the ratio of CTD:Water sample conductivity ratio, also after the CTD pressure and temperature sensors have been corrected using the above coefficients. The CTD is clearly over- estimating the conductivity.

A least square fit was used to determine calibration coefficients for the CTD conductivity ratio:

CR(cor) = CR(ctd)*{a*T(cor) + b*P(cor) + c}

where:

T(cor) and P(cor) are the corrected CTD temperature and pressure
a = -1.787654e-5
b = -5.632200e-7
c = 0.999984

RMS salinity difference between water sample and corrected CTD is 0.005 for 89 data values.

Figs. 6 and 7 illustrate how effective the CTD conductivity and derived salinity have been corrected. The propensity of the CTD to over-estimate salinity has been effectively compensated for by the calibration.

The histograms in Fig. 8 show how well the CTD conductivity is corrected since the upper frame has been derived after the CTD temperature and pressure have been corrected, but before the CTD conductivity calibration has been applied.

If it is assumed that the salinometer is accurate to 0.006 and the CTD salinity to 0.01, then differences between ±0.016 are acceptable. Only 1 of 89 values lies outside this range after the calibrations have been applied; 2 of 89 lie outside ±0.013.

Transmission/Suspended Load

Two transmissometers were used during the cruise, mounted on the CTD rosette. At the Bull Anchorage instrument s/n 479 (with a 5 cm path length) was used whilst s/n 198 (25 cm path length) was used at the other CTD stations.

Each instrument was calibrated in terms of suspended load (mg/1) by comparing the logged %transmission with laboratory determinations of suspended load.

suspended load = a*loge(%Trans) + b

where:

a = -58.91 and b=263.63 for s/n 479
a = -12.42 and b=54.61 for s/n 198

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.

Project Information

Joint Nutrient Study I (JoNuS)

Concerns by the scientific community about the impact of nutrient inputs to the sea; a lack of information on inputs from the UK and on the spatial and temporal distribution and cycling of nutrients in UK waters provided the impetus for the JoNuS project.

The project sought to quantify the input of nitrogen, phosphorus and silicon from UK estuaries to the North Sea through a good understanding of the estuarine processes that control the flow of these nutrients. It focussed on the Great Ouse/Wash and the Humber outflows. Its specific objectives were:

• To measure the fluxes of nutrient elements (N, P, Si) through selected major estuaries on a quantitative annual basis in order to determine the net input to the sea resulting from gross river inputs.
• To quantify the processes controlling the fluxes of nutrients through estuaries.

The Centre for Environment, Fisheries and Aquaculture Science (CEFAS) hosted the project, which involved scientists from CEFAS, the University of East Anglia, the University of Essex, the Plymouth Marine Laboratory and the National Rivers Authority (now the Environment Agency). It was funded by the then Ministry of Agriculture, Fisheries and Food (MAFF) and the Department of Environment, now the Department of Environment, Food and Rural Affairs (Defra).

The project ran from April 1990 to March 1995, with marine field data collection between May 1990 and December 1993. Data collection involved ship based surveys which were complemented by estuarine transects and specific process studies.

Initially, the surveys were on a quarterly basis up to October 1992, however monthly surveys were carried out during 1993. During this intensive survey period, the programme focused on the Great Ouse/Wash; with a continuing, but lower level, of activity devoted to the Humber. An additional multi-project cruise, carried out in January 1995, also complemented the JoNuS data set. Further details of the JoNuS I cruises are provided below:

Data Activity or Cruise Information

Cruise

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:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: