Metadata Report for BODC Series Reference Number 184332


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Guildline Model 8770 Digital CTD  CTD; water temperature sensor
Instrument Mounting research vessel
Originating Country United Kingdom
Originator -
Originating Organization Ministry of Agriculture, Fisheries and Food Lowestoft Fisheries Laboratory (now Centre for Environment, Fisheries and Aquaculture Science Lowestoft Laboratory)
Processing Status banked
Project(s) -
 

Data Identifiers

Originator's Identifier 6/88CI155
BODC Series Reference 184332
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1988-07-18 12:46
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval -
 

Spatial Co-ordinates

Latitude 54.63980 N ( 54° 38.4' N )
Longitude 0.66660 W ( 0° 40.0' W )
Positional Uncertainty 0.1 to 0.5 n.miles
Minimum Sensor Depth 3.96 m
Maximum Sensor Depth 49.84 m
Minimum Sensor Height 4.15 m
Maximum Sensor Height 50.04 m
Sea Floor Depth 54.0 m
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 Instantaneous - Depth measured below water line or instantaneous water body surface
Sea Floor Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
 

Parameters

BODC CODE Rank Units Short Title Title
PRESPR01 1 Decibars Pres_Z Pressure (spatial co-ordinate) exerted by the water body by profiling pressure sensor and corrected to read zero at sea level
PSALPR01 1 Dimensionless P_sal Practical salinity of the water body by conductivity cell and computation using UNESCO 1983 algorithm
TEMPST01 1 Degrees Celsius WC_temp_CTD Temperature of the water body by CTD or STD
 

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


Data Access Policy

Centre for Environment, Fisheries and Aquaculture Science (Cefas) data access conditions

The Centre for Environment, Fisheries and Aquaculture Science (Cefas) is an Executive Agency of the Department of Environment, Food and Rural Affairs (Defra), formerly the Ministry of Agriculture, Fisheries and Food (MAFF). It was also known previously as the Directorate of Fisheries Research (DFR). This data policy refers to data collected by the organisation under all titles.


Narrative Documents

Guildline 8770 CTD profiling system and 8709 probe

The Guildline 8770 is a portable ocean profiling system comprising a probe (model 8709), control unit and winch. Three versions of the probe are available: standard, Artic and batfish. The differences between the versions lie in numbers and types of connectors, and the existence of a protective cage (not present in the batfish version). The probe has a nominal drop rate of 1 ms -1 and a pressure rating of 1000 dbar.

The probe includes a resistance thermometer temperature sensor, a strain gauge pressure sensor, a conductivity cell, a temperature-compensated polarographic dissolved oxygen sensor and a combination pH sensor incorporating a glass measuring electrode and a calomel reference electrode. The probe digitises all measurements, and phase encodes and transmits the data to the control unit.

Specifications

Parameter Range Accuracy (180 days) Display Resolution Response time
Depth 0 to 1000 dbar

Linearity: ± 0.5%

Hysteresis: ± 0.25%

Zero offset: ± 1%

Sensitivity error: ± 1%

0.1 dbar < 1 msec
Temperature -3 to 38.99°C ± 0.02°C 0.01°C 60 msec
Conductivity ratio 0.001 to 1.6 ± 0.0004 0.0002 60 msec
Salinity (calculated) 0.1 to 40 ppt ± 0.04 ppt 0.01 ppt  
pH

6 to 9

2 to 12

± 0.05

± 0.1

0.01 30 sec to 90% for pH 6 or 10°C change
Dissolved Oxygen (calculated) 0 to 15 ppm ± 0.5 ppm (for 90 days) 0.01 ppm

5 sec to 90% for a change in oxygen only

3 min to 50% for a 10°C change in temperature

10 min to 90% for a 10°C change in temperature

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

RV Cirolana Cruise 6/1988 CTD Data Documentation Part 1

Introduction

Documentation for CTD data collected on R.V. Cirolana Cruise 6/88 (June-July 1988) by the Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, UK, under the direction of K. Medler.

Instrumentation

The instrument used was a Guildline Model 8770 CTD. The system consisted of a probe and control unit which measured (or calculated) pressure, conductivity ratio, temperature and salinity. The conductivity sensor was an electrode mounted in pyrex glass, the pressure sensor was a strain gauge element in a four arm resistance bridge network and the temperature sensor was a copper resistance element in a stainless steel tube. The probe electronically measured the parameters and sent the data to the control unit after digitising the results.

The control unit converted the data to binary format, displayed the results, had analog output for chart recording and allowed the data to be recorded on audio cassette. This latter facility was usually a precaution against information loss since data were logged (at 1 sample per second) on either a Hewlett Packard mini computer or an Apricot microcomputer. Salinity was calculated by a microprocessor within the system. The algorithm used was that for the Practical Salinity Scale.

The CTD was mounted on a General Oceanics multisampler fitted with Niskin bottles. This enabled the data to be logged whilst the water sample was being collected. Attaching thermometers to the Niskin bottles allowed comparison to be made between reversing thermometers and the CTD temperature sensor. An altimeter had been fitted to the multisampler, which allowed a comparison to be made with the pressure calibration.

Data Processing

Data were logged every one second. Since the lowering rate was usually less than one metre per second, values were often recorded at between 0.2 and 0.4 decibar intervals. These data have not been averaged. However, they have been plotted to identify spurious readings. Estimates of density were also used to help identify suspect values, but in view of the limited accuracy of the instrument and because the water column was well mixed it is inevitable that some density inversions will exist in the data.

RV Cirolana Cruise 6/1988 CTD Data Documentation Part 2

Calibrations and Data Quality

Both the pressure and temperature sensors of the CTD were calibrated using the pre-cruise laboratory calibration. The salinity of water samples collected at thirty-one stations was used to calibrate the conductivity sensor. After rejecting a few samples because of salinity differences >0.006, a total of 162 samples (mostly from duplicates) remained with which to determine the calibration coefficients.

Pressure

In the past, we have tried to corroborate the laboratory calibration by comparing CTD pressure with thermometric pressures from the DSRT. Because of inaccuracies in the latter, this method is no longer used. We have also considered previously how the sample level could be determined from PDR water depth and altimeter height above the seabed. It was impossible to reconcile these sample levels with the CTD pressure when the instrument was used in deep water. Consequently, the pressure sensor was calibrated before and after the cruise with a dead weight tester. Good agreement was obtained and the pre-cruise calibration was used to correct pressure values.

Temperature

Laboratory calibrations conducted before and after the cruise were in fair agreement. They did suggest a small difference (4 to 10 mK) and an attempt was made to detect a change in the sensor response during the cruise by comparing CTD temperature with those from DSRTs. No evidence for a systematic change was found, but the accuracy of our DSRTs would probably prohibit the detection of a response change of the magnitude suggested by the laboratory calibration.

Temperatures were corrected using the pre-cruise calibration.

Conductivity Ratio

The method adopted was to first calculate the conductivity ratio that the water sample would have, if given its measured salinity, at the pressure and temperature at which it was collected. The ratio of this conductivity to that recorded by the CTD was then fitted by least squares to

[CR(WS)/CR(CTD)]= a x T(CTD) + b x P(CTD) + C
where T(CTD) and P(CTD) are the corrected CTD temperature and pressure.

The rms difference between water sample salinity and CTD salinity was 0.011.

Better agreement was obtained if, for each station, an estimated cell coefficient, based on the mean CR(WS) :CR(CTD) ratio, was evaluated before determining the coefficients a, b and c above. This gave an rms difference of 0.005. In view of the tolerances in CTD and bench salinometer measurements this seems as good agreement that could realistically be expected.

A feature of these data was the apparent change in response of the conductivity sensor during the first eight stations (numbers 24 to 71). This is shown in Fig. 2 which displays the ratio CR(CTD) :CR(WS) for all stations (numbers 24 to 71 and 72 to 103) a closer look at the former group, Fig. 3, suggests that at the first two stations (24 and 39) the ratio is approximately 1.0015 and that it appears to change when the four upper samples are taken at the following station (42), the ratio approaching 1.0025. At the next three stations (44, 56 and 68) the ratio remains near 1.0025 (and in this respect is similar to stations 72 through to 103). During stations 70 and 71, however, the ratio decreases to 1.0015 before increasing to 1.0025.

Subsequent examination of theta-S plots from adjacent stations suggested that, in order to obtain consistent data, it was necessary to assume that the CR(CTD):CR(WS) ratio at station 42 was similar (i.e. approx. 1.0025) to that during stations 44, 56 and 68. The theta-S distributions also indicated that the cell factor derived for station 39 was too large and a better alternative was to assign to this station the cell factor calculated for station 42.

Calibration Coefficients for CTD Data Cirolana 6/1988

Pressure

P(COR) = P(CTD) + PA*T(COR) + PB*P(CTD) + PC where T(COR) = corrected CTD temperature
PA = 6.9646 E-1
PB = 3.85187 E-3
PC = -3.74

Temperature

T(COR) = T(CTD) + TA*T(CTD)*T(CTD) + TB*T(CTD) + TC
where TA = -1.70167 E-5
TB = -7.79426 E-3
TC = -7.3795 E-3

Conductivity Ratio

CR(COR) = CR(CTD) x {CF x (CA x T(COR) + CB x P(COR) + CC)}
where CA = 5.579934 E-5
CB = -3.253974 E-8
CC = 0.9998239
CF is the cell factor for each station as follows:

Station No. Cell Factor Station No. Cell Factor Station No. Cell Factor
24 0.9980783 39 0.9975758 42 0.9975758
44 0.9973358 56 0.9976255 68 0.9972953
70 0.9975061 71 0.9983974 72 0.9976852
73 0.9974241 75 0.9976903 76 0.9976554
77 0.9976174 78 0.9977275 79 0.9977299
80 0.9977350 81 0.9976013 82 0.9977266
83 0.9975244 84 0.9976596 85 0.9976857
86 0.9977118 87 0.9975132 88 0.9975976
89 0.9976082 90 0.9975300 92 0.9976696
94 0.9976939 96 0.9977111 99 0.9975425
102 0.9974842 103 0.9978446

Project Information


No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Cruise Name CIR6/88
Departure Date 1988-06-21
Arrival Date 1988-07-19
Principal Scientist(s)Paul A Gurbutt (Ministry of Agriculture, Fisheries and Food Lowestoft Fisheries Laboratory)
Ship RV Cirolana

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