Metadata Report for BODC Series Reference Number 1124627


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Lockheed Martin Sippican XCTD-2 probe  water temperature sensor; salinity sensor; expendable CTDs
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Dr John Huthnance
Originating Organization Proudman Oceanographic Laboratory (now National Oceanography Centre, Liverpool)
Processing Status banked
Project(s) Oceans 2025
Oceans 2025 Theme 3
Oceans 2025 Theme 3 WP3.1
 

Data Identifiers

Originator's Identifier C4_00547
BODC Series Reference 1124627
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2007-05-12 19:16
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 0.1375 metres
 

Spatial Co-ordinates

Latitude 36.13854 N ( 36° 8.3' N )
Longitude 9.94062 W ( 9° 56.4' W )
Positional Uncertainty 0.01 to 0.05 n.miles
Minimum Sensor Depth 2.06 m
Maximum Sensor Depth 1552.0 m
Minimum Sensor Height -
Maximum Sensor Height -
Sea Floor Depth -
Sensor Distribution Variable common depth - All sensors are grouped effectively at the same depth, but this depth varies significantly during the series
Sensor Depth Datum Approximate - Depth is only approximate
Sea Floor Depth Datum -
 

Parameters

BODC CODE Rank Units Short Title Title
ACYCAA01 1 Dimensionless Record_No Sequence number
CNDCST01 1 Siemens per metre CTDCond Electrical conductivity of the water body by CTD
DEPHCV01 1 Metres Depth Depth below surface of the water body by computation from probe free-fall time using unspecified algorithm
PSALZZXX 1 Dimensionless P_sal Practical salinity of the water body by computation using UNESCO 1983 algorithm
SVELCT01 1 Metres per second CTD_Sound_Vel Sound velocity in the water body by CTD and computation from temperature and salinity by unspecified algorithm
TEMPPR01 1 Degrees Celsius Temp Temperature of the water body
 

Definition of Rank

  • Rank 1 is a one-dimensional parameter
  • Rank 2 is a two-dimensional parameter
  • Rank 0 is a one-dimensional parameter describing the second dimension of a two-dimensional parameter (e.g. bin depths for moored ADCP data)

Problem Reports

No Problem Report Found in the Database

Comments on XCTD data collected during cruise D318

During the screening of the XCTD data it was noticed that in two XCTD casts (C3_00016 and C3_00486), there appeared to be a three cycle delay in the response of derived channels salinity and sound velocity to changes in conductivity. It is unclear what the cause of the offset is or whether this problem affects other casts.

Data quality report - gaps in XCTD-2 data

In nearly all series recorded by the XCTD-2 instrument, there are occurrences where there are large depth differences between adjacent cycles. These large gaps occur at intermittent intervals, with size and frequency varying from cast to cast. The magnitude of the depth differences ranges from a couple of metres to in excess of 50 m between cycles in some series. Although the Data Originator has not provided an explanation for these gaps, there are no indications that they make the data untrustworthy.


Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."


Narrative Documents

Lockheed Martin Sippican XCTD-2 probe

Lockheed Martin Sippican XCTD-2 probe

The expendable CTD profiling system uses an inductive conductivity sensor, thermistor and microprocessor based battery-powered circuitry to internally compute and average the temperature and conductivity of the water column. The XCTD is attached to a wire which is used to digitally transmit the data back to the research vessel. Time since the probe has entered the water is used as a proxy to calculate depth as the descent speed of the XCTD is known. During the manufacturing process the XCTD is calibrated at three temperatures and conductivities which are stored internally and used in the computation of temperature and conductivity prior to data transmission. After transmission the data is processed using the MK21 Data Acquisition System which is available in either ISA or USB configurations. The XCTD-2 Probe can be used within a maximum depth of 1850 m, with a rated ship speed of 3.5 knots. The full specification for this instrument can be found here .

Originator's processing document for D318 XCTD and XBT data

Sampling strategy

A total of 32 Lockhead Martin Sippican expendable conductivity, temperature and depth (XCTD) casts and 515 Lockhead Martin Sippican expendable bathythermograph (XBT) casts were conducted during RSS Discovery cruise D318, which took place in the Gulf of Cadiz (for more information see the D318 cruise report ). The cruise was split up into two legs, D318a and D318b. D318a took place from 17 April 2007 to 23 April 2007, with D318b taking place from 27 April 2007 to 14 May 2007. Of the 32 XCTD casts, 22 were performed using XCTD-1 probes with the remaining 10 performed by XCTD-2 instruments. 496 of the 515 XBT casts were performed using XBT-T5 units with the remaining 19 being performed by XBT-T7 probes.

Deployment

Casts were performed at intervals of approximately 20 minutes. For the first two days every fifth cast was performed by an XCTD, however the use of XCTD probes became more sporadic from 20 April 2007, after the originator noticed spiking in the XCTD-2 data. This resulted in long periods of the cruise where only XBT-T5 instruments were used. The use of XCTDs became even more infrequent during leg D318b, with only 10 XCTD casts being performed.

During D318a, XBT and XCTD deployments occurred simultaneously with the deployment of a towed seismic array (air guns and hydrophone streamer). To combat the possibility of the XBT being entangled in the array the data originator rigged a guide pipe to keep the XBT wire further out on the starboard side of the RSS Discovery. This pipe comprised of around five metres of rubberised tubing with a diameter of approximately six centimetres, which was taped to a metal bar to keep it straight. One end was lashed to the rear starboard side of the ship with the other held outwards by the rear starboard crane at an angle of approximately 45° The lower end of the pipe was approximately three metres starboard of the rear of the ship, one to two metres above the sea surface. When launched the probes fell down the tube and into the sea below, away from the line of the towed array. Although this arrangement worked very well for the most part, some of the longer XCTD probes got stuck and needed to be shaken out of the tube.

Data from the XBT/XCTD sensors was transmitted up a length of copper wire to the Sippican data acquisition system. At the beginning of the cruise the old Sippican ISA data acquisition system was used to communicate with the XBTs and XCTDs, however this system started to pre-trigger the instruments before they hit the water. This led to the scientists switching to the USB system, which remained stable throughout the cruise.

Data processing

The originator processed the XBT and XCTD data for the following:

1) Determination of depth

XBTs and XCTDs measure depth as a proxy of elapsed descent time through the water column (this is a known variable). For D318, the XCTD depths were generated using the standard Sippican conversion equation. The Originator reports however, that for the XBT data the Sippican equation has been found to underestimate depth. They resolved this by using a more accurate equation proposed by Boyd and Linzell (1993) for the T5 and T7 XBTs. The originator reports that a temperature correction from Boyd and Linzell (1993) has also been applied to the XBT data. Additionally, the Originator derived sound velocity in both the XBT and XCTD data. For the XCTDs measured temperature and salinity data were used to compute sound velocity. For the XBTs, sound velocity was derived from the measured temperature data with an assumed constant salinity of 35 PSU.

2) Removal of bad data

The Data Originator reports that spiking was a persistent problem in some of the XCTD casts, rendering some portions of these data too troublesome to use. This was rectified by removing all data that the XCTD processing software flagged as bad data (those not given an 8000 flag by the Sippican software). Additionally, all XBTs which displayed persistent trends or peaks were also excluded from the data sent to BODC.

Calibrations

All XCTDs were purchased specifically for this cruise. Prior to transmission the data was calibrated using internally stored calibration coefficients calculated at three different temperatures and conductivities.

References

Boyd J.D., Linzell R.S., 1993. The Temperature and Depth Accuracy of Sippican T-5 XBTs. Journal of Atmospheric and Oceanic Technology. 10, pp 128-136.

Processing of D318 XCTD data by BODC

The Sippican XCTD data were supplied to BODC in the form of 32 ASCII files. Following standard BODC procedure, the data files were reformatted into BODC internal format using an internal transfer function. This table shows how the variables present in the XCTD data files were mapped to appropriate BODC parameter codes.

Originator's variable Description Units BODC parameter code Units Comments
Depth Depth below surface of the water body by computation from probe free-fall time using unspecified algorithm m DEPHCV01 m -
Temperature Temperature of the water body by CTD or STD °C TEMPPR01 °C -
Conductivity Electrical conductivity of the water body by CTD mS cm -1 CNDCST01 S m -1 To convert mS cm -1 into S m -1 the original conductivity values were divided by 10
Salinity Salinity of the water body by CTD ppt (parts per thousand) PSALZZXX - Check of Sippican processing manual shows salinity derived as practical salinity, not in parts per thousand as quoted
Sound velocity The rate at which sound travels through the water column m s -1 SVELCT01 m s -1 -
Density - kg m 3 - - This variable was not transferred.
Status - - - - This variable was not transferred.

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. In many of the XCTD casts, especially those performed by the XCTD-1 instrument, it was apparent that it took the conductivity sensor a few seconds to acclimatise. In these cases the first few cycles of the conductivity channel and any parameters derived from conductivity have been flagged.

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:

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:

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:

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

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:

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:

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:

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

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:

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 3: Shelf and Coastal Processes

Over the next 20 years, UK local marine environments are predicted to experience ever-increasing rates of change - including increased temperature and seawater acidity, changing freshwater run-off, changes in sea level, and a likely increase in flooding events - causing great concern for those charged with their management and protection. The future quality, health and sustainability of UK marine waters require improved appreciation of the complex interactions that occur not only within the coastal and shelf environment, but also between the environment and human actions. This knowledge must primarily be provided by whole-system operational numerical models, able to provide reliable predictions of short and long-term system responses to change.

However, such tools are only viable if scientists understand the underlying processes they are attempting to model and can interpret the resulting data. Many fundamental processes in shelf edge, shelf, coastal and estuarine systems, particularly across key interfaces in the environment, are not fully understood.

Theme 3 addresses the following broad questions:

Within Oceans 2025, Theme 3 will develop the necessary understanding of interacting processes to enable the consequences of environmental and anthropogenic change on UK shelf seas, coasts and estuaries to be predicted. Theme 3 will also provide knowledge that can improve the forecasting capability of models being used for the operational management of human activities in the coastal marine environment. Theme 3 is therefore directly relevant to all three of NERC's current strategic priorities; Earth's Life-Support Systems, Climate Change, and Sustainable Economies

The official Oceans 2025 documentation for this Theme is available from the following link: Oceans 2025 Theme 3

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


Oceans 2025 Theme 3, Work Package 3.1: Global Impacts of Shelf Seas

At the margins of the shelf seas, steep shelf-slope bathymetry has impacts on ocean circulation and the transmission of signals around the ocean basins (Hughes and Meredith, 2006), while dense water formation and cascades at the shelf edge are thought to be important for water mass formation (Ivanov et al., 2004) and for the off-shelf transport of organic and inorganic carbon (e.g. Wollast and Chou, 2001).

In this Work Package, the Proudman Oceanographic Laboratory (POL) aim to quantify the water fluxes between the shelf and open ocean globally, including the development of methods to incorporate shelf effects into global models. Greater understanding of the whole carbon cycle will benefit from combining this work on down-slope fluxes of water (and its constituent dissolved carbon) with work in Oceans 2025 Theme 5 (down-slope transports of sediments and particulate carbon).

The specific objectives are:

More detailed information on this Work Package is available at pages 5 - 27 of the official Oceans 2025 Theme 3 document: Oceans 2025 Theme 3

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

Some data used in Work Package 3.1 were collected to complement work carried out on the European Union's Geophysical Oceanography (GO) project. For these data, linkage to the GO project documentation is provided

References:

Hughes CW. and Meredith MP., 2006. Coherent sea level fluctuations along the global continental slope. Phil Trans Roy Soc A, 364, 885-901.

Ivanov VV., Shapiro GI., Huthnance JM., Aleynik DL. and Golovin PN., 2004. Cascades of dense water around the world ocean. Progr in Oceanogr, 60(1), 47-98.

Wollast R. and Chou L., 2001. Ocean margin exchange in the northern Gulf of Biscay: OMEX I. An introduction. Deep Sea Res II 48, 2971-2978.

Yool A. and Fasham MJR., 2001. An examination of the 'continental shelf pump' in an open ocean general circulation model. Global Biogeochem Cycles, 15, 831-844.


Data Activity or Cruise Information

Cruise

Cruise Name D318B
Departure Date 2007-04-27
Arrival Date 2007-05-14
Principal Scientist(s)Richard W Hobbs (University of Durham, Department of Earth Sciences)
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