Metadata Report for BODC Series Reference Number 1161484

• 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 Quality report: turbidity flags on Liverpool Viking ferry data

In nearly all series, values were flagged when the ferry approached Liverpool as the turbidity level exceeded the measurement range of the sensor. Flags were frequently applied to turbidity values measured on approach to Dublin Port for the same reason.

Liverpool - Dublin ferry data quality report: turbidity spike repetition

In many of the series recorded by the FerryBox system on the Liverpool - Dublin ferry, there is spiking in the turbidity sensor which occurs every 360 cycles (i.e. at the same cycle every hour). The precise time which the spiking occurs is consistent through each deployment period - the period each sensor set was present on the ferry until it was rotated by the originator. Thus, if the spike occurs at hh:30:15 in one series, it will occur at the closest cycle to this time in all other series of that particular deployment period. The size of these spikes also shows considerable variation. While many such spikes exceed the measurement range of the sensor, others are only a couple of FTU greater than their surrounding cycles.

Not all series are affected by this issue, and in series that are often only some of the cycles in this pattern produce a spike. If a series lasting from 09:00 to 15:00 has spikes at hh:51:08, then it may be that there are only spikes at 09:51:08, 12:51:08 and 14:51:08, with the other cycles showing normal values. The cycles affected by this issue have been flagged by BODC, however the cause of the problem is not known.

Data quality report for Liverpool Viking from Dublin to Birkenhead on 14 March 2009

In this series there was a period between 12: 43 UTC and 12:48 UTC which saw an increase in dissolved oxygen concentration, a decrease in salinity and several spikes in the turbidity channel. This event occurred in the central Irish sea approximately 20 km north west of Anglesey. The changes observed in each variable have been summarised below:

• Salinity: Salinity dropped from 33.95 to 33.54 in one and a half minutes before values gradually recovered over the following three minutes and a half minutes.
• Turbidity: There were a few spikes in the salinity data recorded over this period.
• Dissolved oxygen: The effects of this event lasted longer in the dissolved oxygen channel than they did in turbidity or salinity. Initially, oxygen concentration increased from below 250 µ mol l^-1 to nearly 400 µ mol l^-1 in just over one minute, at which point values appear to be outside the range of the sensor. Dissolved oxygen concentration stayed at this level until 13:16 UTC, after which values decreased gradually until 13:51 UTC. Between 13:51 UTC and 13:56 UTC concentration fell from 367.5 µ mol l^-1 to 248.9 µ mol l^-1. All cycles which were recorded during this period have been flagged by BODC.

Data Access Policy

Open 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.

If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:

"Contains public sector information licensed under the Open Government Licence v1.0."

Narrative Documents

Chelsea Instruments MINI^tracka Fluorometer

The MINI^tracka Fluorometer is an in-situ optical sensor that uses a single high intensity LED light source and, according to the manufacturer, is designed to enhance rejection of ambient daylight. The fluorometer provides a linear response between chlorophyll concentration and fluorometer voltage.

Sensor specifications, current at August 2006, are given in the table below. More information can be found at the manufacturer's specification sheet.

Sensor Specifications

Aanderaa Oxygen Optodes models 3835, 4130, 4175, 3830, 3930 and 3975

The Aanderaa Oxygen Optode is based on the ability of selected substances to act as dynamic fluorescence quenchers. The fluorescent indicator is a special platinum porphyrin complex embedded in a gas permeable foil that is exposed to the surrounding water.

A black optical isolation coating protects the complex from sunlight and fluorescent particles in the water. This sensing foil is attached to a window providing optical access for the measuring system from inside a watertight titanium housing.

The foil is excited by modulated blue light, and the phase of a returned red light is measured. By linearizing and temperature compensating, with an incorporated temperature sensor, the absolute O₂ concentration can be determined. According to the manufacturer, the lifetime-based luminescence quenching principle offers the following advantages over electro-chemical sensors:

• Not stirring sensitive (it consumes no oxygen)
• Less affected by fouling
• Measures absolute oxygen concentrations without repeated calibrations
• Better long-term stability
• Less affected by pressure
• Pressure behaviour is predictable
• Faster response time

The 3835, 4130 and 4175 models are designed to operate down to 300 m, while there are two versions of the 3830, 3930 and 3975 models, designed to operate down to 2000 m and 6000 m, respectively. The sensors fit directly on to the top end-plate of Recording Current Meter RCM 9, and other Aanderaa instruments. Sensor specifications may be viewed via the following links: Aanderaa Oxygen Optodes 3835/4130/4175 and Aanderaa Oxygen Optodes 3830/3930/3975.

Seapoint Turbidity Meter

The Seapoint Turbidity Meter detects light scattered by particles suspended in water, generating an output voltage proportional to turbidity or suspended solids. Range is selected by two digital lines which can be hard wired or microprocessor controlled, thereby choosing the appropriate range and resolution for measurement of extremely clean to very turbid waters. The offset voltage is within 1 mV of zero and requires no adjustment across gains. The optical design confines the sensing volume to within 5 cm of the sensor allowing near-bottom measurements and minimizing errant reflections in restricted spaces.

Sensor specifications, current at August 2006, are given in the table below.

Sensor Specifications

** output is non-linear above 750 FTU.

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

Citadel TS-N Thermosalinograph

The Teledyne RD Instruments Citadel TS-N Thermosalinograph is a compact low-maintenance system in a through-flow housing, designed for mounting on ships or gliders down to 500m. Conductivity is measured by Teledyne RDI's Nonexternal-Field Inductive Conductivity (NXIC) sensor, with temperature measurements performed by an aged thermistor. Prior to 2009 this instrument was manufactured by Falmouth Scientific (FSI).

The full specification for this instrument is available here.

Laipac GD30-L GPS logger

The Laipac GD30-L is a high performance Global Positioning System (GPS) recorder and vehicle tracking system which can be used for passive tracking applications. The recording interval is programmable and can be set anywhere in between three seconds and 30 minutes. The data recorded by this GPS includes date, time, longitude, latitude, speed, trajectory, and number of tracking satellites.

Instrument description document for Liverpool - Dublin ferry data

The originator used a FerryBox system attached to the DFDS Seaways Liverpool to Dublin ferry to collect the data. Two complete sets of instruments were used, each of which comprised of an FSI NXIC CTD, Chelsea Minitracka II fluorometer and a Seapoint Turbidity Meter. From 28 April 2008 an Aanderaa Oxygen Optode was attached to the FerryBox system. The originator rotated each set of instruments approximately every two weeks, so that while one set was mounted on the ship the other was being serviced on land.

Attached to underway from 28-04-2008

Originator's processing document for Liverpool - Dublin ferry data

Sampling strategy

A total of 1492 time series were collected by a FerryBox system mounted on the DFDS Seaways Liverpool to Dublin Ferry route from 18 November 2007 to 23 January 2011. The system consisted of a GPS logger LAIPAC GD30L, Falmouth Scientific conductivity, temperature, depth probe (FSI NXIC CTD), Chelsea Minitracka II fluorometer and a Seapoint turbidity meter. From 28 April 2008 an Aanderaa Oxygen Optode was attached to the FerryBox system, which was fed by water entering the ship at a depth of three metres below the sea surface.

Data checks by data originator

In-situ cross-checking

For temperature and salinity, in-situ quality checks were performed by comparing the FSI CTD data with temperature and salinity from the Cefas SmartBuoy, which was located in the Irish Sea close to the Liverpool Seaways' route between Liverpool and Dublin. This comparison found a high degree of similarity between the FSI CTD data and that from the SmartBuoy, thus the data originator decided that it was not necessary to apply any calibrations to these data.

Measurement error checking

All the sensors used had manufacturers calibrations applied prior to their first deployment. No calibrations based on independent water samples were applied to the data, but laboratory checks were performed to verify the correct operation of the FSI CTD, Seapoint Turbidity Meter and Chelsea Minitracka. The methods for these tests have been detailed below.

• FSI NXIC CTD

• The operation of the FSI CTD was checked on several occasions. Each check was carried out against a water sample collected during a specific Coastal Observatory cruise, using the following method:

  • Each time a water sample was collected, it was analysed after the cruise by Bangor University using a Portasal precision salinometer. Each sample was then used to fill a bucket, providing a reference container of a known salinity.
  • The tip of a pt100 Platinum resistance (PRT) 'smart' temperature probe was placed in the bucket to provide an independent check of temperature.
  • The reading generated by the PRT probe was recorded using a Tinsley-ASL F200 precision digital thermometer.
  • The FSI CTD was placed in the bucket so that the conductivity cell was fully immersed.
  • Over several minutes a series of temperature, conductivity and salinity readings were taken to confirm that the measurements had stabilised.
  • Once the CTD had acclimatised to the bucket, three consecutive readings of temperature, conductivity and salinity were taken. The mean of these measurements was used to compare the FSI CTD readings with the reference values.
  • The FSI CTD was cleaned, placed back in the water bucket and the measurement process was repeated.

• Seapoint turbidity meter

• The manufacturer's tolerance for turbidity readings is ± 2% for the 0 to 25 FTU, 25 to 100 FTU and 100 to 500 FTU ranges. This experimental procedure was designed to verify the turbidity sensor is maintaining this accuracy. The complete method was as follows:

  • The face of the turbidity meter was covered with opaque tape and a turbidity reading was recorded.
  • A turbidity reading in air was recorded.
  • A turbidity reading was recorded in a bucket containing 10 litres of filtered water. The reading was taken when the face of the turbidity meter was at least 10 cm away from the bucket walls and the water air interface.
  • Another bucket was filled with 10 litres of filtered water.
  • A bottle of 3980 FTU stock solution was shaken so as to evenly distribute the suspension
  • 15 ml of stock suspension was measured, added to the 10 litre bucket of water, and stirred to evenly dilute the stock solution. This should have produced a bucket of water with a turbidity of 5.97 FTU.
  • A turbidity reading was recorded in a bucket containing the 5.97 FTU water solution. The reading was taken when the face of the turbidity meter was at least 10 cm away from the bucket walls and the water air interface.
  • The last four steps were repeated for dilutions of 30 ml and 50 ml stock solutions, to test turbidity values of 11.94 FTU and 19.97 FTU respectively

• Chelsea Minitracka II

• Readings were taken with the sensor in air, immersed in filtered water and using a 4x10^-10 Molar Rhodamine reference block to test for any measurement offsets that may occur if the sensor reading has changed significantly since it was calibrated.

Salinity drift correction

Over the period that the Liverpool to Dublin ferry was measuring data, the originator became aware that the salinity measurements were liable to drift between servicings. This was identified as being due to the gradual accumulation of sediment on the conductivity sensor of the FSI unit.

When this drift was identified, the originator compensated for it by adding a standard offset to the salinity channel in every series in a deployment period (a timescale of approximately two weeks between servicing visits). The offset was calculated by comparing the maximum salinities of each deployment period and examining by how much the maximum salinity dropped off in the later series. This was done as the originator hypothesised that the maximum salinity should not experience much variation over a two week period.

During the measurement period covered by this series, an offset of 0.015 has been added to the salinity channel.

Time correction

Time has been corrected by the data originator to compensate for a 5 minute lag in hydraulics, from when the water entered the hull until it reached the underway monitoring system. The correction of this ensured time in the data files corresponded to the correct GPS position at the time of the measurement.

Processing of Liverpool - Dublin ferry data by BODC.

The data arrived at BODC in the form of 1205 ASCII format .txt files representing underway data taken on Irish Sea crossings by the DFDS Liverpool Seaways ferry from 02 June 2008 to 23 January 2011. Following standard BODC procedure, the 1205 files were reformatted into BODC standard internal format using an internal transfer function. The following table shows how the originator's variables were mapped to the appropriate BODC parameter codes:

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.

References

Benson B.B., and Krause D. jnr., 1984. The concentration and isotopic fractionation of oxygen dissolved in fresh water and seawater in equilibrium with the atmosphere. Limnol. Oceanogr. 29, pp.620-632.

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.

Liverpool - Dublin ferry instrumentation servicing group two

Project Information

Oceans 2025 - The NERC Marine Centres' Strategic Research Programme 2007-2012

Who funds the programme?

The Natural Environment Research Council (NERC) funds the Oceans 2025 programme, which was originally planned in the context of NERC's 2002-2007 strategy and later realigned to NERC's subsequent strategy (Next Generation Science for Planet Earth; NERC 2007).

Who is involved in the programme?

The Oceans 2025 programme was designed by and is to be implemented through seven leading UK marine centres. The marine centres work together in coordination and are also supported by cooperation and input from government bodies, universities and other partners. The seven marine centres are:

• National Oceanography Centre, Southampton (NOCS)
• Plymouth Marine Laboratory (PML)
• Marine Biological Association (MBA)
• Sir Alister Hardy Foundation for Marine Science (SAHFOS)
• Proudman Oceanographic Laboratory (POL)
• Scottish Association for Marine Science (SAMS)
• Sea Mammal Research Unit (SMRU)

Oceans2025 provides funding to three national marine facilities, which provide services to the wider UK marine community, in addition to the Oceans 2025 community. These facilities are:

• British Oceanographic Data Centre (BODC), hosted at POL
• Permanent Service for Mean Sea Level (PSMSL), hosted at POL
• Culture Collection of Algae and Protozoa (CCAP), hosted at SAMS

The NERC-run Strategic Ocean Funding Initiative (SOFI) provides additional support to the programme by funding additional research projects and studentships that closely complement the Oceans 2025 programme, primarily through universities.

What is the programme about?

Oceans 2025 sets out to address some key challenges that face the UK as a result of a changing marine environment. The research funded through the programme sets out to increase understanding of the size, nature and impacts of these changes, with the aim to:

• improve knowledge of how the seas behave, not just now but in the future;
• help assess what that might mean for the Earth system and for society;
• assist in developing sustainable solutions for the management of marine resources for future generations;
• enhance the research capabilities and facilities available for UK marine science.

In order to address these aims there are nine science themes supported by the Oceans 2025 programme:

• Climate, circulation and sea level (Theme 1)
• Marine biogeochemical cycles (Theme 2)
• Shelf and coastal processes (Theme 3)
• Biodiversity and ecosystem functioning (Theme 4)
• Continental margins and deep ocean (Theme 5)
• Sustainable marine resources (Theme 6)
• Technology development (Theme 8)
• Next generation ocean prediction (Theme 9)
• Integration of sustained observations in the marine environment (Theme 10)

In the original programme proposal there was a theme on health and human impacts (Theme 7). The elements of this Theme have subsequently been included in Themes 3 and 9.

When is the programme active?

The programme started in April 2007 with funding for 5 years.

Brief summary of the programme fieldwork/data

Programme fieldwork and data collection are to be achieved through:

• physical, biological and chemical parameters sampling throughout the North and South Atlantic during collaborative research cruises aboard NERC's research vessels RRS Discovery, RRS James Cook and RRS James Clark Ross;
• the Continuous Plankton Recorder being deployed by SAHFOS in the North Atlantic and North Pacific on 'ships of opportunity';
• physical parameters measured and relayed in near real-time by fixed moorings and ARGO floats;
• coastal and shelf sea observatory data (Liverpool Bay Coastal Observatory (LBCO) and Western Channel Observatory (WCO)) using the RV Prince Madog and RV Quest.

The data is to be fed into models for validation and future projections. Greater detail can be found in the Theme documents.

Oceans 2025 Theme 10

Oceans 2025 is a strategic marine science programme, bringing marine researchers together to increase people's knowledge of the marine environment so that they are better able to protect it for future generations.

Theme 10: Integration of Sustained Observations in the Marine Environment spans all marine domains from the sea-shore to the global ocean, providing data and knowledge on a wide range of ecosystem properties and processes (from ocean circulation to biodiversity) that are critical to understanding Earth system behaviour and identifying change. They have been developed not merely to provide long-term data sets, but to capture extreme or episodic events, and play a key role in the initialisation and validation of models. Many of these SOs will be integrated into the newly developing UK Marine Monitoring Strategy - evolving from the Defra reports Safeguarding our Seas (2002) and Charting Progress (2005), thus contributing to the underpinning knowledge for national marine stewardship. They will also contribute to the UK GOOS Strategic Plan (IACMST, 2006) and the Global Marine Assessment.

Weblink: http://www.oceans2025.org/

Oceans 2025 Theme 10, Sustained Observation Activity 11: Liverpool Bay and Irish Sea Coastal Observatory

Sustained, systematic observations of the ocean and continental shelf seas at appropriate time and space scales allied to numerical models are key to understanding and prediction. In shelf seas these observations address issues as fundamental as 'what is the capacity of shelf seas to absorb change?' encompassing the impacts of climate change, biological productivity and diversity, sustainable management, pollution and public health, safety at sea and extreme events. Advancing understanding of coastal processes to use and manage these resources better is challenging; important controlling processes occur over a broad range of spatial and temporal scales which cannot be simultaneously studied solely with satellite or ship-based platforms.

Considerable effort has been spent by the Proudman Oceangraphic Laboratory (POL) in the years 2001 - 2006 in setting up an integrated observational and now-cast modelling system in Liverpool Bay (see Figure), with the recent POL review stating the observatory was seen as a leader in its field and a unique 'selling' point of the laboratory. Cost benefit analysis (IACMST, 2004) shows that benefits really start to accrue after 10 years. In 2007 - 2012 exploitation of (i) the time series being acquired, (ii) the model-data synthesis and (iii) the increasingly available quantities of real-time data (e.g. river flows) can be carried out through Sustained Observation Activity (SO) 11, to provide an integrated assessment and short term forecasts of the coastal ocean state.

Overall Aims and Purpose of SO 11

• To continue and enlarge the scope of the existing coastal observatory in Liverpool Bay to routinely monitor the northern Irish Sea
• To develop the synthesis of measurements and models in the coastal ocean to optimize measurement arrays and forecast products. Driving forward shelf seas' operational oceanography with the direct objective of improving the national forecasting capability, expressed through links to the National Centre for Ocean Forecasting (NCOF)
• To exploit the long time-series of observations and model outputs to: a) identify the roles of climate and anthropogenic inputs on the coastal ocean's physical and biological functioning (including impacts of nutrient discharges, offshore renewable energy installations and fishing activity) taking into consideration the importance of events versus mean storms / waves, river discharge / variable salinity stratification / horizontal gradients; b) predict the impacts of climate change scenarios; and c) provide new insights to Irish Sea dynamics for variables either with seasonal cycles and interannual variability, or which show weak or no seasonal cycles
• To provide and maintain a 'laboratory' within which a variety of observational and model experiments can be undertaken (Oceans 2025 Themes 3, 6, 8, 9), including capture of extreme events
• Demonstrate the value of an integrated approach in assessment and forecasting
• Demonstrate the coastal observatory as a tool for marine management strategies through collaboration with the Environment Agency (EA), Department for Environment, Food and Rural Affairs (DEFRA), Joint Nature Conservation Commmittee (JNCC), English Nature (EN), Department of Agriculture and Rural Development (DARD), and Local Authorities, providing management information pertinent to policy (e.g. Water Framework Directive)

Measurement and Modelling Activities

• East Mooring Site: Bottom frame with full suite of physical measurements (high frequency Acoustic Doppler Current Profiler (ADCP), conductivity, temperature, turbidity and fluorescence), a Centre for Environment, Fisheries and Aquaculture Science (CEFAS) directional wavebuoy, and a CEFAS Smartbuoy collecting surface properties including salinity, temperature, turbidity, nutrients, irradiance and chlorophyll. All transmit data in real-time via Orbcomm. The Smartbuoy also collects daily water samples.
• West Mooring Site: Bottom frame with full suite of physical measurements (high frequency ADCP, conductivity, temperature, turbidity and fluorescence), CEFAS Smartbuoy.
• Spatial Survey: Four - six week intervals (determined by biofouling of optical sensors). Spatial surveys comprise of vertical profiles of CTD, suspended particulate material (SPM), some bed sediment sampling and surface and bed nutrients, phytoplankton, zooplankton.
• Ferry: The Birkenhead - Belfast ferry samples near surface (5 m depth) temperature, salinity, turbidity, chlorophyll, with data transmitted by Orbcomm. The route is scientifically varied passing through six completely different hydrodynamic regions, which significantly impact on their ecological function.
• Tide gauges: Real-time data are obtained from tide gauges operated by Mersey Docks and Harbour Company (MDHC) and the UK tide gauge network.
• Satellite imagery: Weekly composite satellite data, Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature (SST) and ocean colour (chlorophyll and suspended sediment), are provided by the Remote Sensing Data Analysis Service (RSDAS) based at Plymouth Marine Laboratory (PML).
• HF radar: A phased array HF radar system (a 12-16MHz WERA HF radar) measuring surface currents and waves with maximum range 75km at a resolution of 4km for sea surface currents and for 2-D wave spectra.
• Meteorology station: With web camera, located on Hilbre Island at the mouth of the Dee Estuary
• Operational models: The Coastal Observatory uses Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS), which is part of Oceans 2025 Theme 9.

More detailed information on this Work Package is available at pages 32 - 35 of the official Oceans 2025 Theme 10 document: Oceans 2025 Theme 10

Weblink: http://www.oceans2025.org/

References:

IACMST., 2004. The Economics of Sustained Marine Measurements. IACMST Information Document, N0.11, Southampton: IACMST, 96 pp

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Liverpool Viking ferry route from Dublin to Birkenhead

The Liverpool Bay Coastal Observatory project included sustained underway measurements collected by a FerryBox system attached to the DFDS Seaways Liverpool Viking commercial ferry. The area surveyed for this project has been illustrated in the map below.

The box in the above map was created from the maximum and minimum latitude and longitude of all data points recorded between 18 November 2007 and 23 January 2011.

Sampling history

The ferry collected measurements twice daily from 18 November 2007 to 23 January 2011, once in each direction between Dublin Port and Birkenhead. Sensors measuring temperature, salinity, turbidity and chlorophyll were present as part of the Ferrybox system for the entire data collection period. In addition to these sensors, a dissolved oxygen sensor was added from 28 April 2008. A summary of the instruments used in the FerryBox system has been provided below.

Two sensor packages were used, each comprising of a complete set of the instruments listed in the table above. The Data Originator rotated each package approximately every two weeks so that each set of instruments could be cleaned and calibration verification checks performed.

Data quality comments

Any problems that have been found with these data have been written up as data quality reports and linked to the relevant series. A summary of the main problems found has been provided below:

• The maximum salinity observed during each crossing was found to be drifting between servicings, due to a built up of sediment on the conductivity sensor. The Data Originator compensated for this by adding an offset to the salinity values in all deployment periods where a drift was observed.
• There are small offsets between the dissolved oxygen data recorded by each sensor which start to become noticeable between deployment periods 78 and 79, which begins on 03 September 2009.
• The minimum chlorophyll recorded by the fluorometer starts to increase with each consecutive sailing during the second half of many deployment periods. When these data are compared to the first few series of the following deployment period, the chlorophyll values from these series appear significantly elevated. BODC recommend these data be used with caution as the reason for this increasing minimum is not known.
• In quite a few series there are periods which see a simultaneous change in the values of two or more parameters. These changes usually comprise a brief period where there is a steep change in the value of multiple parameters, followed by a longer period where these values recover back to values which fit the trend observed before the initial change. Almost all of these events include an increase in turbidity nd a decrease in salinity, however often the temperature, dissolved oxygen and/or chlorophyll channels are also affected.
• In some series there are gaps in the data. These gaps take two forms, either there is a short period of data at the beginning of the profile followed by a gap lasting from a few minutes to several hours, or there is a step change in temperature and often other parameters, followed by a gap in the data exactly 29 cycles later. It appears that in most series with the first issue, the cycles before the gap were recorded before the crossing began. Where this is the case these cycles have been flagged. The cause of the second issue is unknown.
• In a few series anomalously high dissolved oxygen concentrations were observed during the first half of the crossing.
• There is an issue with the turbidity data recorded after 18 May 2009 whereby there was a spike at the same cycle every hour (occasionally in later series, every 45 minutes).

Some of the issues that only affect individual series or deployment periods are provided in the table below.

Related Fixed Station activities are detailed in Appendix 1

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:

Appendix 1: Liverpool Viking ferry route from Dublin to Birkenhead

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.