Metadata Report for BODC Series Reference Number 596294


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Seapoint chlorophyll fluorometer  fluorometers
LI-COR LI-192 PAR sensor  radiometers
Falmouth Scientific Instruments Integrated CTD Profiler  CTD; water temperature sensor; salinity sensor
Instrument Mounting research vessel
Originating Country United Kingdom
Originator -
Originating Organization Centre for Environment, Fisheries and Aquaculture Science Lowestoft Laboratory
Processing Status banked
Project(s) -
 

Data Identifiers

Originator's Identifier CO08/01/34
BODC Series Reference 596294
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2001-08-17 10:30
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 1.0 decibars
 

Spatial Co-ordinates

Latitude 55.82920 N ( 55° 49.8' N )
Longitude 2.18230 E ( 2° 10.9' E )
Positional Uncertainty Unspecified
Minimum Sensor Depth 3.0 m
Maximum Sensor Depth 82.2 m
Minimum Sensor Height 4.8 m
Maximum Sensor Height 84.0 m
Sea Floor Depth 87.0 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
CPHLPR01 1 Milligrams per cubic metre chl-a_water_ISfluor Concentration of chlorophyll-a {chl-a CAS 479-61-8} per unit volume of the water body [particulate >unknown phase] by in-situ chlorophyll fluorometer
FVLTWS01 1 Volts WsVolt Instrument output (voltage) by linear-response chlorophyll fluorometer
IRRDUV01 1 MicroEinsteins per square metre per second SubsurVPAR Downwelling vector irradiance as photons (PAR wavelengths) in the water body by cosine-collector radiometer
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
PSALST01 1 Dimensionless P_sal_CTD Practical salinity of the water body by CTD 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

In the salinity channel there are large spikes and null values that have been flagged on the thermocline. This could be due to a mismatch between the conductivity cell and the thermistor.

The chlorophyll concentration channel is very noisy.


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

Falmouth Scientific Integrated CTD (ICTD) Profiler

The FSI ICTD is designed to collect high precision conductivity, temperature and pressure data with self calibrating electronics. This instrument can support five primary sensors (including up to three temperature sensors) and can be coupled with a water bottle sampler. The ICTD is equipped with a titanium housing rated to 7000 m and has a sampling rate of 32 Hz.

Three temperature sensors are available: primary platinum, redundant platinum and exposed thermistor. Any combination of these can be used in the primary channels. The instrument also has multiple RS-232 serial inputs for a variety of sensors including: ADCP, Benthos PSA-916 Altimeter and WetLabs SAFire. There are an additional eight DC input channels that can support virtually any sensor that has a DC output.

Specifications:

Parameter Conductivity Temperature Pressure
Sensor Inductive cell Platinum thermometer Precision-machined Silicon
Range 0 to 70 mS cm -1 -2 to 35°C Customer specified
Accuracy ±0.002 mS cm -1 0.002°C ±0.01 % full scale
Resolution 0.0001 mS cm -1 0.00005°C 0.0004 % full scale
Response 5.0 cm at 1 ms -1

150 ms Platinum

20 ms Thermistor*

25 ms

*Optional

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

Seapoint Chlorophyll Fluorometer

The Seapoint Chlorophyll Fluorometer (SCF) is a low power instrument for in situ measurements of chlorophyll a. The SCF uses modulated blue LED lamps and a blue excitation filter to excite chlorophyll a. The fluorescent light emitted by the chlorophyll a passes through a red emission filter and is detected by a silicon photodiode. The low level signal is then processed using synchronous demodulation circuitry which generates an output voltage proportional to chlorophyll a concentration. The SCF may be operated with or without a pump.

Sensor specifications, current at August 2006, are given in the table below. More information can be found at the manufacturer's web site .

Sensor Specifications

Power requirements 8 - 20 VDC, 15 mA avg., 27 mA pk.
Output 0 - 5.0 VDC
Output Time Constant 0.1 sec.
Power-up transient period < 1 sec.
Excitation Wavelength 470 nm CWL, 30 nm FWHM
Emission Wavelength 685 nm CWL, 30 nm FWHM
Sensing Volume 340 mm 3
Minimum Detectable Level 0.02 µg l -1

  Gain Sensitivity, V µg -1 l -1 Range, µg l -1
Sensitivity/Range 30x
10x
3x
1x
1.0
0.33
0.1
0.033
5
15
50
150

LI-COR LI-192 Underwater Quantum Sensor

The LI-192 Underwater Quantum Sensor is used to measure photosynthetic photon flux density and is cosine corrected. The sensor is often referred to as LI-192SA or LI-192SB (the LI-192SB model was superseded by LI-192SA). One of the main differences is that the LI-192SA model includes a built-in voltage output for interfacing with NexSens iSIC and SDL data loggers.

Sensor specifications, current at January 2012, are given in the table below. More information can be found in the manufacturer's LI-192SA and LI-192SB specification sheets.

Sensor Specifications

(Specifications apply to both models unless otherwise stated)

Absolute Calibration ± 5 % in air traceable to NBS.
Sensitivity Typically 3 µA per 1000 µmol s -1 m -2 for LI-192SB and 4 µA per 1000 µmol s -1 m -2 for LI-192SA in water.
Linearity Maximum deviation of 1 % up to 10,000 µmol s -1 m -2 .
Stability < ± 2 % change over a 1 year period.
Response Time 10 µs.
Temperature Dependence ± 0.15 % per °C maximum.
Cosine Correction Optimized for both underwater and atmospheric use.
Azimuth < ± 1 % error over 360 ° at 45 ° elevation.
Detector High stability silicon photovoltaic detector (blue enhanced).
Sensor Housing Corrosion resistant metal with acrylic diffuser for both saltwater and freshwater applications. Waterproof to withstand 800 psi (5500 kPa) (560 meters).

RV Corystes Cruise 08/01 CTD Data Documentation

35 full depth CTD profiles were obtained using a FSI CTD s/n 1366 during this cruise to the North Sea during August 2001; see Figure1. Station 86 is not shown in figure 1 because it was distant from all other stations , at 56.241N, 5.238 E. Samples were collected for salinity analysis (using a Guildline salinometer) to derive a calibration for the instrument conductivity sensor and a single pair of digital reversing thermometers used to compare with the CTD temperature estimates. A Seapoint fluorometer sensor and a LICOR photosynthetically active radiation sensor with a six-decade log amplifier were fitted to the rosette for all stations. A turbidity sensor was also fitted for stations 1 to 20, and this was replaced with an oxygen sensor for stations 34 to 86. Chlorophyll samples were collected to calibrate the fluorometer.

(a) Pressure

The pressure sensor was calibrated using a dead-weight tester on 6/08/2001 at 14 degC and atmospheric pressure 1005mb. This suggested that the CTD sensor was reading too low by 2.3db. During the cruise the 'on deck' CTD pressure immediately prior to lowering the CTD was recorded. For stations 1 to 11, this consistently indicated that the sensor was reading too low by approximately 2.7db. Adjustments were made to the CTD pressure sensor, and for stations 12 to 86, this consistently indicated that the sensor was reading too low by approximately 0.1db. These 'on deck' observations have been used to correct recorded CTD pressure as follows:

P(cor) = P(unc) + dP

Stations 1 to 11

dP= 2.7db

Stations 12 to 86

dP= 0.1db

(b) Temperature

The PRT temperature sensor fitted to the CTD was calibrated using PRT's on 06/08/2001, and this was used to correct the CTD temperature :

T(cor) = T(unc) + dT

dT = a*T(unc)*T(unc) + b*T(unc) + c

where a = -1.4913e-5 b = 1.5034e-4 c = -7.8879e-5

This is equivalent to a correction between 0 and 3 millidegC in the range 6 to20 degC.

A pair of electronic thermometers was fitted to one Niskin bottle, sampling close to the seabed. The difference between the temperatures from thermometers and CTD is plotted in Figure 2.

(c) Conductivity

The difference between salinometer and CTD salinity before any corrections are applied to the sensors is plotted in Figures 3a and b. The CTD salinity is an under-estimate with a mean difference of 0.028 for stations 1 to 20, and 0.014 stations 34 to 57. This offset changes to 0.027 (stat 1 to 20) and 0.014 (stat 34 to 57) after the pressure and temperature calibrations have been applied, standard deviation 0.005 and 0.007 respectively, as shown in Figures 4a and b.

Figures 5a and b show conductivity ratio(CTD)/ conductivity ratio(water samples), the water sample conductivity ratio being that from the salinometer salinity at the corrected pressure and temperature given by the CTD. The CTD conductivity is being under-estimated.

To compensate for this a least square fit was used to determine appropriate calibration coefficients:

CR(cor) = CR(ctd) [a*T(cor) + b*P(cor) + c]

where T(cor) and P(cor) are the corrected CTD temperature and pressure and

Stations 1 to 20

a = -0.569968871e-04, b = -0.336904302e-05, c = 1.00177905, rms = 0.004, N = 17

Stations 34 to 57

a = 0.149446123e-04, b = 0.218913847e-05, c = 1.00011429, rms = 0.006, N = 41

Figures 6, 7, 8 and 9 show how effective these coefficients are in correcting the CTD salinity. The histograms of Figures 8 and 9 show the differences before and after the application of the conductivity coefficients. Figures 8a and b show the differences after calibrations applied to temperature and pressure sensors; Figures 9a and b after temperature, pressure and conductivity calibrations have been applied. If it assumed that the CTD is accurate to 0.01 and the salinometer to 0.003 then differences of +/-0.013 are acceptable. In this instance 2 differences (fig9b) are not within +/-0.013.

Station 86 only

This station gave larger differences between the water sample salinity and uncorrected CTD salinity than all other stations, possibly due to the presence of jellyfish.

Pcor Tcor Sctd(unc) Sws Sws-Sctd
50.40 7.294 34.875 34.907 0.032
35.60 7.487 34.870 34.907 0.037
10.40 16.797 34.877 34.925 0.048

Therefore a calibration was done for station 86 only.

a = 0.175024132e-05, b = -0.102146743e-04, c = 1.0013116, rms = 0.0, N = 3

Fluorometer - Chlorophyll Calibration

A Seapoint fluorometer (s/n 2289) was fitted to the rosette sampler and used to estimate chlorophyll levels. The sensor was calibrated by comparing recorded voltages with measured chlorophyll of samples collected in Niskin bottles as the CTD returned to the surface. The instrument was operated on two ranges during the cruise, gain x 30 for stations 1 to 37, and gain x 10 for stations 38 to 86. Stations 1 to 37 also covered 2 distinct areas, therefore giving 3 linear regression calibrations for the whole cruise. See figures 10a, 10b and 10c.

Chlorophyll = a * Fluorometer (volts) + b

Stations 1 to 20

a = 3.3636 b = -1.923 R2 = 0.5126

Stations 34 to 37

a = 1.499 b = -0.2153 R2 = 0.921

Stations 38 to 86

a = 3.9698 b = -0.5077 R2 = 0.804

Suspended Loads

A Seapoint turbidity sensor (s/n1610) was fitted to the rosette for stations 1 to 20, and used to estimate suspended load levels. The sensor was calibrated by comparing recorded voltages with measured suspended load samples collected as the CTD returned to the surface. See fig 11

Suspended load = a * SPNT turbidity(volts) + b

Stations 1 to 20

a = 5.6529 b = 0.6416 R2 = 0.9522

Oxygen Sensor

An oxygen sensor was fitted to the rosette for stations 34 to 57. No calibrations were done, and the recorded volts were retained in files called CORY0801S*.NEW17SEC_OXY only, in the column usually reserved for suspended load.

Photosynthetically Active Radiation

The LICOR light sensor (s/n 5672) used to measure photosynthetically active radiation was calibrated during June 2001 using a standard lamp. This gave an in-air current of 0.819 microAmp per 217.1 micromolesm-2s-1, equivalent to 0.3499 micromolesm-2s-1 per nanoAmp in water.

Sue Norris
06/11/2001

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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


No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Cruise Name COR8/01
Departure Date 2001-08-14
Arrival Date 2001-08-29
Principal Scientist(s)Juan Brown (Centre for Environment, Fisheries and Aquaculture Science Lowestoft Laboratory)
Ship RV Corystes

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