Metadata Report for BODC Series Reference Number 436984

• 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

RRS Discovery 189 SeaSoar Data

Introduction

Documentation for the SeaSoar data collected on board RRS Discovery cruise 189 09/03 - 08/04 1990 by the Institute for Oceanographic Sciences under Brian A King.

Instrumentation

Data were collected from a Niel Brown Mk III CTD, deployed in the IOSDL SeaSoar vehicle. The vehicle cycled between the surface and approximately 380m, the depth reached depending mainly on towing speed and sea state. The SeaSoar made 4 sections centred in 17, 15, 12 and 9 °W.

Data Processing and Calibration

Sampling

CTD data were passed from the CTD deck unit to a Level A interface, and then to a SUN workstation for processing using the PSTAR suite of data processing programs. The CTD data were sampled at 8Hz, and reduced to one second averages by the level A.

Initial Calibration

Program CTDCAL was used to provide initial calibration of pressure, temperature, conductivity and to compute salinity. The following equations were used:

Pcal(dbar)=0.999098*(0.01*Praw)-0.5
Tcal(C)=0.9990762*(0.0005*Traw)-0.009374
Ccal(mmho/cm)=1.00527*(0.001*Craw)

The pressure offset was chosen to be the observed deck offset, and the temperature calibration was from the most recent laboratory calibration (9 February 1990). Prior the start of SeaSoar work, the CTD was lowered from the midships winch to 600m, and samples collected in Niskin Bottles for salinity calibration. This provided the initial cell conductivity ratio.

Salinity was calculated from 1983 equations of state after speeding up the response of the platinum thermometer with a time constant of 0.23 seconds. The time constant was chosen from early SeaSoar Data by over plotting down and up Theta-S curves and adjusting the time constant to minimise hysteresis between them.

Gridding

The gridding consisted of assigning data to bins 8dbar deep and 4 km along track, followed by averaging of all data in a bin. Usually bins contain 15 or more one-second averages.

Navigation was by GPS (at least 16 hours a day) and transit satellite.

Final Salinity Calibration

The final salinity calibration was achieved by comparing samples drawn from the ships non-toxic seawater supply once per hour (155 samples were used for the final calibration) and analysed using a Guildline Autosal, with the averaged salinity values between 0 and 5m depth from each SeaSoar surfacing event. The resulting file of differences was then smoothed using a 21 point running average. The residuals of bottle-SeaSoar salinities, after this correction procedure, had the following statistics:

• 91% of the residuals had magnitude no greater than 0.005
• 98% no greater than 0.01
• The standard deviation of the residuals was 0.003

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

No Project Information held for the Series

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: