Metadata Report for BODC Series Reference Number 57622

• 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

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

Specifications

These specification apply to the MK3C version.

Further details can be found in the specification sheet.

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.

RRS Discovery Cruise 162 CTD Data Documentation

Introduction

This document covers the CTD data collected on RRS Discovery Cruise 162 (September - October 1986) by the Institute of Oceanographic Sciences (Deacon Laboratory) Godalming, Surrey, UK., under the direction of P. M. Saunders.

Instrumentation

The instrument used was a Neil Brown Instrument Systems CTD which measured pressure, temperature and conductivity and was fitted with a Beckman dissolved oxygen electrode. The CTD was used alongside a General Oceanics Rosette Multisampler with 12 water bottles, a 10kHz pinger, a bottom echo-sounder and a Sea-Tech transmissometer.

Sampling Protocol

Lowering and retrieval rates of 0.5 to 1.5 m/s were employed and the sensors were flushed with distilled water on recovery. Bottle samples and reversing thermometer measurements were made on ascent and the sea water samples were analysed using a Guildline Autolab salinometer. Reversing thermometers were calibrated before and after the cruise.

Calibration

Pressure

The calibration equation based on laboratory measurements was taken to be:

P = 0.1 * PRAW - 12.0

Differences between the pressure measured by the CTD and by pairs of reversing thermometers are shown in the table below.

Temperature

The calibration equation used was:

T = 0.00049953*TRAW+0.026.

A comparison between CTD temperatures and reversing thermometers is given in the table below. The calibration of the same platinum resistance thermometer has remained very stable since it was acquired in 1983 showing a range of only 0.002 at 2.5 °C and 0.004 at 20 °C. The comparison with the reversing thermometers is excellent.

Salinity

In the North East Atlantic the sample measurements show very little scatter about a linear potential temperature (POTT) - Practical Salinity (S) relationship for POTT less than 2.6 °C of:

S = 34.698 + 0.098 * POTT

The cell factor required to bring the CTD salinities into agreement with this equation are calculated for each station. The table below compares salinities derived from the rosette sampler and Guildline salinometer with the CTD values.

Oxygen

From a sample value of oxygen concentration (determined by the Winkler method) the fractional saturation content was obtained by normalising it by the appropriate saturation value. The Beckman oxygen cell also measures fractional saturation F, given by the equation:

ln F = ln I + ln C + aT + bp

where

I = oxygen probe current
T = weighted temperature (0.25*T(ambient) + 0.75*T(oxygen))
p = pressure

The cell factor was taken as 1.409, a as 0.05/°C and b as 0.0000955/db. These constants were used throughout the cruise and the fit of CTD oxygens and sample values is shown in the table below.

Transmittance

Potential transmittance, which takes account of the increasing mass of clear water in the 1m path of the instrument with increasing pressure, was calculated. The instrument SN035 was employed and corrections were made for the air calibration (4.31), manufacturer's provided sensitivity (1.0032) and change in refractive index with pressure, temperature and salinity.

Fit of CTD data to Rosette Sample Values

Data Processing

Original values were averaged over an interval of one second and calibration coefficients and correction factors applied. A time constant correction algorithm was employed to compensate for the slower response of the platinum resistance thermometer.

Differences between successive values of each parameter were examined; the mean difference and its standard deviation calculated and values greater than several standard deviations from the mean difference were checked. Genuinely suspect data were then replaced by interpolated values.

Derived quantities were computed from algorithms published by Fofonoff and Millard (1983). To remove the effect of ships heave data cycles were sorted by pressure before all values were averaged at 5db intervals, centred on 2.5db, 7.5db and so on

References

Saunders, P. M. and Cooper, F. 1987.
CTD data on the Iberian Abyssal Plain. Institute of Oceanographic Sciences, Report No. 247.

Fofonoff, N.P. and Millard Jr., R.C. 1983,
Algorithms for the computation of fundamental properties of sea water. UNESCO Technical Paper on Marine Science 44.

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: