Metadata Report for BODC Series Reference Number 541766

• 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 current speed or direction are available for this instrument.

The instrument's recorded pressure indicated a depth deeper than the total water depth measured on deployment by the ship's echo-sounder by at least 10 metres. Absolute pressure values from this instrument should therefore be used with caution.

The attenuance time-series shows that the transmissometer saturated at 9.9 per metre. Records reaching this value were flagged '>'.

Towards the end of the record from 1 May 1999 03:00, the attenuance signal indicated a final 'event' which was identified as suspect by the data originators (SPM group, UNW, Bangor) and which was probably due to the battery getting flat. Records from 1 May 1999 03:00 have therefore been flagged as suspect.

The data originators also highlighted that a few attenuance values were below 0.364 per metre which is the typical value for particle free water at 660 nm in these instruments. The minimum value for data points not flagged as suspect was 0.22 per m. Although these low values were isolated and of small magnitude, they could suggest that the transmissometer reading of beam attenuation was underestimating the real value. Absolute attenuance value from this instrument should therefore be used with caution.

Throughout the record, the salinity and conductivity values appear low (by ca. 0.5 PSU for salinity) relative to concomitant conductivity/salinity measurements obtained from other instruments deployed close to this instrument position and depth.

Absolute salinity values from this instrument should therefore be used with caution.

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

Aanderaa Recording Current Meter Model 7/8

Manufacturer's specifications: recording unit height 49.5cm (RCM8 52.0cm), diameter 12.8cm, vane size 48.5x50.0cm. Meter is designed for depths down to 2000m (RCM8 6000m). It incorporates a spindle which is shackled to the mooring line. The meter is attached to the spindle through a gimbal mounting which permits a maximum 27° deviation of the spindle from the vertical, the meter still remaining horizontal.

Meter comprises :

1. Paddle wheel rotor magnetically coupled to an electronic counter

2. Vane, which aligns instrument with current flow, has a balance weight ensuring static balance and tail fins to ensure dynamic balance in flows up to 250cm/s.

3. Magnetic compass (needle is clamped to potentiometer ring) - direction recorded with 0.35° resolution, 5° accuracy for speeds 5 to 100cm/s, 7.5° accuracy for remaining speeds within 2.5 to 200cm/s range.

4. Quartz clock, accuracy better than 2 sec/day within temperature range 0 to 20°C.

5. Thermistor (temperature sensor), standard range -2.46 to 21.48°C (max on high range 36.04°C), accuracy 0.05°C, resolution 0.1 per cent of range, 63 per cent response time 12sec.

6. Inductive cell conductivity sensor (optional), range 0 to 70mmho/cm standard resolution 0.1 per cent of range.

7. Silicon piezoresistive bridge, standard range 0 to 3000 psi (RCM8 to 9000 psi), resolution 0.1% of range.

8. Self balancing potentiometer which converts the output from each sensor into a 10 bit binary number for storage on magnetic tape.

9. Associated electronics.

A built-in clock triggers the instrument at preset intervals and up to six channels are sampled in sequence. Channel 1 is a fixed reference reading for control purposes and data identification. Channels 2, 3 and 4 represent measurement of temperature, conductivity and pressure. Channels 5 and 6 represent the VECTOR AVERAGED current speed and direction since the previous triggering of the instrument. The number of rotor revolutions and the direction is sampled every 12 seconds and broken into North and East components. Successive components are added and recorded as speed and direction. For recording intervals longer than 10 minutes, speed and direction are sampled 1/50th of recording interval.

It has become common practice in some laboratories to deploy these meters as temperature and conductivity loggers without current measuring capabilities.

The following link will provide the manufacturer specifications:

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.

Aanderaa Current Meter Data Processing

Data Originator's Processing

The following procedures are carried out before the data were supplied to BODC.

Data were downloaded from the instrument logger, and factory calibrations were applied to the current speed channel, and the pressure, conductivity and temperature channels when fitted. Where available, laboratory calibrations of the current direction channels were used; factory formulae were used in their absence. Where no form factor was known for the conductivity sensor, a value of 2.8 was used.

Please note (concerns vector averaged current data): The current data are averaged by the logger over the sampling interval, whereas the pressure, temperature and conductivity data are single point measurements taken at the end of the interval. The data originator has moved the time stamps to the mid-point of the vector averaging sampling interval for all channels without interpolation.

BODC Data Processing and Quality Control

Where pressure sensors were fitted: the data record was compared with the pressure computed from the water depth on deployment and rig geometry. The time series was visually screened for evidence of rig movement (e.g. trawling) and excessive leaning (perhaps due to strong currents).

Where temperature sensors were fitted: the data record was compared with calibrated CTD data taken in the vicinity and checked for agreement within a few tenths of a degree Celsius. Obvious spikes were flagged. Periods of excessively noisy data were noted.

Where conductivity sensors were fitted: salinity (PSS-78) was computed from in-situ temperature and conductivity and a nominal pressure computed from the water depth on deployment and rig geometry. Obvious spikes were flagged.

Data Processing Notes

Transmissometer Calibration (University of Wales, Bangor, UK)

Transmission readings from the SeaTech transmissometer interfaced with the Aanderaa current meter SN11814 were converted to attenuance using the following values:

Air correction reading = 653
Blanked path reading = 0

These values were determined following a pre-deployment in situ calibration cast when the two SeaTech transmissometers to be used during the PROVESS SNS mooring experiment were strapped to the CTD frame during Pelagia PE136 cruise (CTD001). The CTD was then lowered to the bed, brought back close to the surface and held at this depth for 5 minutes (see BODC documentation 66467 for further details on calibration procedure).

SeaTech Transmissometer Data Processing

Deployment/Recovery Procedure

(A. Banaszek/ P.Knight, Proudman Oceanographic Laboratory, Birkenhead)

Prior to deployment, the counts logged by the transmissometer in free air and with the light path blocked were recorded. It was then strapped to the CTD frame, lowered into the water and held at a fixed depth for approximately 20 minutes for intercalibration with the CTD transmissometer.

On recovery the data were downloaded from the instrument logger and supplied to BODC as raw counts.

Post-Cruise Calibration

(Dr. S.E. Jones, University of Wales, Bangor)

The raw transmission counts were compared with fully corrected CTD attenuance data from the intercalibration cast. The air-correction counts reading (ACR) for each deployment was found from inversion of the formula:

Atten = -(1/p) * ln { (counts-BPR) / (ACR - BPR) }

where:

Atten = CTD attenuance (per metre)
p = path length (metres)
counts = datalogger reading (counts)
BPR = blocked path reading (counts)
ACR = air correcion reading (counts)

Air correction reading values for each instrument deployment were passed on to BODC.

BODC Data Processing and Quality Control

The data were then converted from data logger counts to attenuance (per metre) by applying the above calibration formula to each datacycle in the series.

The data were visually screened for evidence of fouling on the optics, leaking power connectors and flat batteries. Obvious spikes and any features believed to be of non-oceanographic origin were flagged suspect.

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

PROcesses of Vertical Exchange in Shelf Seas (PROVESS)

Introduction

PROVESS was an interdisciplinary study of the vertical fluxes of properties through the water column and the surface and bottom boundary layers. The project was funded by the European Community MAST-III programme (MAS3-CT97- 0159) and ran from March 1998 to May 2001.

Scientific Rationale

PROVESS was based on the integration of experimental, theoretical and modelling studies with the aim of improving understanding and quantification of vertical exchange processes in the water column, in particular in the surface and benthic boundary layers and across the> pycnocline. PROVESS also explored mechanisms of physical-biological coupling in which vertical exchanges and turbulence significantly affect the environmental conditions experienced by the biota with particular reference to aggregation, flocculation, sedimentation and trophic interactions.

Fieldwork

The experimental phase of the project was carried out at two contrasting sites in the North Sea: the northern North Sea site (NNS) and the southern North Sea site (SNS).

The two sites had the following characteristics:

At both locations measurements were concentrated at a central position with additional measurements being made to estimate horizontal gradients. Moored instruments (including current meters, temperature and pressure sensors, fluorometers, transmissometers, nutrient analysers and meteorological sensors) were deployed between 7 September and 5 November 1998 at the NNS and between 29 March and 25 May 1999 at the SNS. Each experiment was supported by intensive measurement series made from oceanographic ships and involving turbulence dissipation profiler CTD, particle size profilers, optical profilers, benthic sampling and water bottle sampling.

Details of the cruises were as follows:

Data Activity or Cruise Information

Data Activity

PROVESS Project POLRIG#820

This mooring was known within PROVESS as either 'Rig A' or the STABLE mooring. It was one of a cluster of moorings deployed at the main focus of the Southern North Sea Site during the spring of 1999. The rig was deployed by RV Pelagia (cruise PE136) in March 1999 and recovered by RV Belgica (cruise BG9912) in May 1999.

Notes:

• No data were returned for the electromagnetic current meter or the STD-12 due to problems with the STABLE data logger.
• The Aanderaa was fixed to the STABLE frame to measure temperature, salinity and attenuance. Consequently, there are no current measurements from this instrument.

Related Data Activity activities are detailed in Appendix 1

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

PROVESS Southern North Sea Site

Eleven mooring packages were deployed at PROVESS Southern North Sea site by Pelagia cruise PE136 in March 1999. One of these (Rig U) was lost, the NIOZ mooring was recovered by PE136 in April 1999 and the remaining nine were recovered by either RV Belgica cruise BG9912 (8 moorings) or RV Zirfea (Rig V) in May 1999.

The layout of the mooring array was:

The asterisk represents an array of five moorings as detailed in the inset map.

Mooring data

The data returned from each rig were as follows:

CTD data

A total of 356 CTD casts were also collected during the three cruises surveying this area. These include:

Additonal data

Supporting meteorological data (including sea surface temperature and wave statistics) from two platforms (52° 33' N, 4° 3.5' E and 52° 16.4' N, 4° 17.8' E) were supplied to the project and are held by BODC. These series run from the beginning of March 1999 until the end of May 1999.

Related Fixed Station activities are detailed in Appendix 2

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: POLRIG#820

Related series for this Data Activity 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.

Appendix 2: PROVESS Southern North Sea Site

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.