Metadata Report for BODC Series Reference Number 952990

Metadata Summary

Data Description

Data Category Surface temp/sal
Instrument Type
SeaTech transmissometer  transmissometers
Chelsea Technologies Group Aquatracka fluorometer  fluorometers
Global Positioning Satellite System  NAVSTAR Global Positioning System receivers
Alpkem RFA/2 colorimetric autoanalyser  colorimeters; autoanalysers
OceanData TSG103 thermosalinograph  thermosalinographs; water temperature sensor; salinity sensor
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Dr Alan Morris
Originating Organization Plymouth Marine Laboratory
Processing Status banked
Online delivery of data Download available - Ocean Data View (ODV) format
Project(s) LOIS River-Atmosphere-Coast Study (RACS)

Data Identifiers

Originator's Identifier CH99_SURF
BODC Series Reference 952990

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1992-12-07 09:15
End Time (yyyy-mm-dd hh:mm) 1992-12-20 08:14
Nominal Cycle Interval 30.0 seconds

Spatial Co-ordinates

Southernmost Latitude 49.91617 N ( 49° 55.0' N )
Northernmost Latitude 55.91933 N ( 55° 55.2' N )
Westernmost Longitude 5.86933 W ( 5° 52.2' W )
Easternmost Longitude 2.30500 E ( 2° 18.3' E )
Positional Uncertainty 0.05 to 0.1 n.miles
Minimum Sensor or Sampling Depth 4.0 m
Maximum Sensor or Sampling Depth 4.0 m
Minimum Sensor or Sampling Height -
Maximum Sensor or Sampling Height -
Sea Floor Depth -
Sea Floor Depth Source -
Sensor or Sampling Distribution Fixed common depth - All sensors are grouped effectively at the same depth which is effectively fixed for the duration of the series
Sensor or Sampling Depth Datum Approximate - Depth is only approximate
Sea Floor Depth Datum -


BODC CODERankUnitsTitle
AADYAA011DaysDate (time from 00:00 01/01/1760 to 00:00 UT on day)
AAFDZZ011DaysTime (time between 00:00 UT and timestamp)
ALATGP011DegreesLatitude north (WGS84) by unspecified GPS system
ALONGP011DegreesLongitude east (WGS84) by unspecified GPS system
ATTNMR011per metreAttenuation (red light wavelength) per unit length of the water body by 20 or 25cm path length transmissometer
CPHLUW011Milligrams per cubic metreConcentration of chlorophyll-a {chl-a CAS 479-61-8} per unit volume of the water body [particulate >unknown phase] by Aquatracka fluorometer immersed in non-toxic supply and calibration against sample data
NTRIAAD21Micromoles per litreConcentration of nitrite {NO2- CAS 14797-65-0} per unit volume of the water body [dissolved plus reactive particulate <0.4/0.45um phase] by filtration and colorimetric autoanalysis
NTRZAAD21Micromoles per litreConcentration of nitrate+nitrite {NO3+NO2} per unit volume of the water body [dissolved plus reactive particulate <0.4/0.45um phase] by filtration and colorimetric autoanalysis
PHOSAAD21Micromoles per litreConcentration of phosphate {PO43- CAS 14265-44-2} per unit volume of the water body [dissolved plus reactive particulate <0.4/0.45um phase] by filtration and colorimetric autoanalysis
PSALSG011DimensionlessPractical salinity of the water body by thermosalinograph and computation using UNESCO 1983 algorithm and calibration against independent measurements
SLCAAAD21Micromoles per litreConcentration of silicate {SiO44- CAS 17181-37-2} per unit volume of the water body [dissolved plus reactive particulate <0.4/0.45um phase] by filtration and colorimetric autoanalysis
TEMPSG011Degrees CelsiusTemperature of the water body by thermosalinograph and verification against independent measurements
TSEDTR011Milligrams per litreConcentration of suspended particulate material {SPM} per unit volume of the water body [particulate >unknown phase] by in-situ optical attenuance measurement and calibration against sample data

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

CH99 Hydrography Data Quality Report


It should be noted that the fluorometer calibration applied was taken from another cruise, as no extracted chlorophyll data were available from CH99.


A number of values have been flagged as suspect where areas of high suspended load were experiencedd resulting in the transmissometer becoming saturated. In addition, there were two periods (from 23:20 on 13/12/1992 to 09:40 on 14/12/1992 and 08:40 to 12:20 on 16/12/1992) when it is believed that the instrument was not functioning correctly, probably due to interrupted flow from the non-toxic supply. These data have been flagged and should 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

Alpkem RFA-2, RFA-300 and Astoria colorimetric autoanalysers

The Alpkem rapid flow analysers (RFA) and Astoria analyser are continuous flow analysers consisting of a sampler, peristaltic pump, analytical cartridge, heating bath, colorimeter, data station, and printer. The sample and reagant are pushed into the reaction cartridge by the pump, where air-segmentation bubbles are introduced to facilitate mixing. The solution is then analysed colorimetrically, with the absorbance of a specific wavelength of light being indicative of the concentration of the solution. These autoanalysers may be used to measure nutrient concentrations in seawater.

The Alpkem rapid flow analysers were manufactured by OI Analytical, with the RFA-300 being a precursor to the smaller RFA-2 (also known as the RFA II or RFA/2). Astoria Pacific Inc. bought the RFA line, upgraded the instrument and renamed it the Astoria analyser.

The Astoria analyser incorporates a six-channel digital detector, which allows analysis of four to six parameters from a single sample. The components of the system are the 311 XYZ Sampler, 322 Auxiliary Pump (for sampler wash), 302D Micropump (peristaltic pump), 303A Cartridge Base, with room for up to six chemistries, and 305D Digital Detector. The six channels of the 305D allow for extra channels that can be used for reference signals, and optional detectors (fluorometer, UV, and Flame) can be plugged into the system as well.

Aquatracka fluorometer

The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.

The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.

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

Global Positioning Satellite System

A location system of unspecified make or model that determines location on the Earth's surface using the Global Positioning Satellite Network. Angular co-ordinates are given relative to WGS84 CRS. Other parameters such as platform velocity may be derived from this.

SeaTech Transmissometer


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.



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.

CH99 Sea surface hydrography instrument details

Underway hydrography was recorded by a suite of instruments in the ship's flow-through system. Instrument details are given in the table below.

Instrument type Make and model
GPS unspecified
Thermosalinograph TSG103
Fluorometer Chelsea Instruments Aquatracka
Transmissometer SeaTech 661nm, 25cm path

CH99 Hydrography Processing Notes


The nutrients were measured using a Technicon AA2 auto-analyser connected to the pumped seawater supply by a continuous filter block (Morris et al, 1978). The chemistries used were:

Nitrate: Reduced to nitrite by a Cu/Cd coil, then reacted with sulphanilamide in acidic conditions to form a diazo compound that coupled with N-1-naphylethylenediamide dihydrochloride to form a reddish-purple azo dye.
Nitrite: As for nitrate without the reduction step.
Phosphate: Reduction of a phosphomolybdate complex in acid solution to 'molybdenum blue' by ascorbic acid with sensitivity enhanced by the catalytic action of antimony potassium tartrate.
Silicate: Reduction of a silicomolybdate solution to 'molybdenum blue' by ascorbic acid with the addition of oxalic acid to eliminate interference from phosphates.

The colorimeter outputs were logged by a Level A connected to the chart recorder inputs. The system was calibrated by running nutrient-depleted seawater washes to determine baseline and sets of four standards. Standards were generally run at least once per day.

The following processing procedures were adopted by BODC to convert the raw voltage streams into nutrient concentrations.

The data were then segmented into periods with constant colorimeter gain and baseline settings determined from the analyst's notes and examination of the chart records. The data were further segmented if non-linear baseline drift was observed. A baseline equation of the form:

Baseline voltage = Cycle number * coefficient_1 + coefficient_2

was determined for each segment and applied to give a standardised baseline of zero. The voltages measured whilst standards were being run were then used to construct calibration curves to convert raw voltages into nutrient concentrations. These were then applied on a segment by segment basis to the data stream. All baseline and calibration equations were checked manually before they were used. Once concentrations had been calculated and checked, the custom flags for baselines and standards were changed to 'suspect'. The data were subsequently quality controlled by inspection on a graphics workstation with particular attention paid to the concentrations obtained for the standards. These checks included comparative screening between the nutrient channels.

The nutrient time channels were adjusted to correct for the delay incurred whilst the sample passed through the complex plumbing of the auto-analyser. No salt corrections (corrections for difference in optical density between sample and standards) were applied as the standards were prepared in nutrient- depleted seawater.

The time corrections applied were:

Nutrient Time Shift
NO3 -11mins 30secs
NO2 -7mins 30secs
PO4 -12mins
SiO4 -11mins 40secs

Due to the chemistry used for the nitrate analysis, interference from nitrite is inevitable. The nitrate channel has been processed throughout as nitrate+nitrite and no attempt has been made to correct for nitrite.


Chlorophyll was measured by a Chelsea Instruments Aquatracka immersed in a light-tight pond. The fluorometer was calibrated by regressing the natural log of extracted chlorophyll concentration against corresponding fluorometer voltage. The following relationship was hence derived and used to compute the chlorophyll concentrations:

Chlorophyll (mg m-3) = exp (1.1560*fluorometer voltage - 2.0970) (n=105,R2=53.3%)

Sea surface temperature and salinity

Temperature and salinity were measured using an autoranging TSG103 thermosalinograph. The temperature sensor was a thermistor in the non-toxic supply inlet manifold. Conductivity was measured by a unit in the ship's wet laboratory, which included a second thermistor to provide temperature for the computation of salinity.

The raw ADC counts were calibrated to give conductivity and two temperature channels based upon laboratory calculations by RVS. Salinity was computed from the housing temperature and conductivity using the UNESCO 1978 Practical Salinity Scale (Fofonoff and Millard, 1983).

The thermosalinograph was calibrated against surface values taken from the calibrated CTD. A following salinity dependent correction (found by linear regression) was applied to the salinity channel.

Corrected Salinity = Raw salinity + (0.00585 * Raw salinity - 0.166)

The temperature channel exhibited a constant offset except for one short period of the cruise where the offset jumped by approximately 0.1°C. The following corrections were applied:

Start time End time Temperature correction(°C)
09:15:00 07/12/92 06:09:00 16/12/92 -0.13
06:09:30 16/12/92 11:51:30 16/12/92 -0.21
11:52:00 16/12/92 08:14:00 20/12/92 -0.13

Optical Attenuance and Sediment Load

Optical attenuance was measured using a SeaTech red light (661nm) transmissometer with a 25cm optical path length mounted in a light-tight box on the starboard deck continuously flushed by the non-toxic supply.

Transmissometer air readings made during the cruise (4.745 V) were used to correct the transmissometer voltage to the manufacturer's specified air voltage (4.745 V) by ratio. The voltages were then converted to attenuance to eliminate the influence of instrument path length using the equation:

Attenuance = -4.0 * loge (voltage/5.0)

The attenuance data were calibrated as total suspended load using gravimetric SPM determinations on samples taken from the non-toxic supply during the cruise. The calibration determined was:

SPM = (Attenuance + 1.479)/0.2613 (n=11, R2=96.2)


Fofonoff, N.P. and Millard Jr., R.C. (1983). Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science 44.

Morris, A.W., Howland, R.J.M., and Bale, A.J. (1978). A filtration unit for use with continuous autoanalytical systems applied to highly turbid waters. Est. Coast. Mar. Sci. 6, 105-109.

CH99 Sea surface Hydrography, Meteorology and Navigation Series


Seawater was continuously pumped from the hull of the ship (at a depth of about 4m) through the various underway sensors on-deck and in the lab. This is known as the ship's non-toxic supply. An outlet of this, situated in the ship's wet laboratory, was used to collect the calibration samples for the underway sensors.

Data Acquisition

For most parameters, data logging and initial processing was handled by the RVS ABC system. The Level A sampling microcomputer digitised an input voltage, applied a time stamp and transferred the data via the Level B disk buffer onto the Level C where the data records were assembled into files. Sampling rates varied from 10 seconds to several minutes. The Level C included a suite of calibration software, which was used to apply initial calibrations to convert raw ADC counts into engineering units. At the end of the cruise the Level C disk base was transferred to BODC for further processing.

BODC Data Processing Procedures

Data from the underway files were merged into a common file (the binary merge file) using time as the primary linking key. Data logged as voltages (e.g. PAR, nutrients) were converted to engineering units. Each data channel was inspected on a graphics workstation and any spikes or periods of dubious data were flagged. The power of the workstation software was used to undertake all possible comparative-screening checks between channels.

Project Information

LOIS River-Atmosphere-Coast Study (LOIS - RACS)


The Land-Ocean Interaction Study (LOIS) was a NERC research programme designed to study processes in the coastal zone. The Rivers, Atmosphere and Coasts Study (RACS) was a major component of LOIS that looked at land-sea interactions in the coastal zone and the major exchanges (physical, chemical and biological) between rivers and estuaries and the atmosphere. The study focused on the east coast of the UK from the Wash to the Tweed.

RACS included several sub-components

RACS (A) was coordinated by the University of East Anglia and RACS (C) by the Plymouth Marine Laboratory.


The bulk of the RACS (A) data set was collected during two field campaigns in the winter (October/November) of 1994 and the summer (May/June) of 1995. During these campaigns data were collected continuously from the University of East Anglia Atmospheric Observatory at Weybourne on the north Norfolk coast. An instrumented vessel was stationed offshore to provide a second sampling site to allow changes in a given air mass to be monitored. The Imperial College Jetstream research aircraft made one flight during each campaign to provide a link between the two surface stations. The Jetstream made four additional flights in 1996 and 1997.


The coastal oceanographic survey

The coastal oceanographic data set was collected during a series of 17 RRS Challenger cruise legs. Most cruises covered two survey grids. One from Great Yarmouth to the Humber designed around the distribution of the sandbanks and a second simple zig-zag grid from the Humber to Berwick on Tweed. A large number of anchor stations, usually over one or two tidal cycles, were worked in the area of the Humber mouth or the Holderness coast.

The Humber estuarine study

The Humber estuarine data set was collected during a series of 33 campaigns on the Environment Agency vessels Sea Vigil and Water Guardian in the Humber, Trent and Ouse river systems at approximately monthly intervals between June 1993 and December 1996. Each campaign consisted of two or three one-day cruises. The tracks covered the estuary from the tidal limits of both Trent and Ouse to Spurn Point. Instrumental and sample data are available from a series of fixed stations that were sampled during every campaign.

The Tweed estuarine study

The Tweed estuarine data set was collected during a series of 13 campaigns using RV Tamaris in association with a rigid inflatable vessel at approximately monthly intervals between July 1996 and July 1997. Each campaign covered the tidal reaches of the River Tweed.

The Holderness experiment

The Holderness Experiment was designed to monitor the process of sediment transport along the Holderness coastline. It consisted of three moored instrument deployments during the winters of 1993-1994, 1994-1995 and 1995-1996. Mooring platforms were deployed at eight stations along two lines off the Holderness coast. A northerly and a southerly line of four stations each were used (N1 - N4 and S1 to S4) with the lowest numbers being inshore. Both lines were approximately perpendicular to the coast, although the S4 station lay to the south of the S line, off Spurn Head.

Data Activity or Cruise Information


Cruise Name CH99
Departure Date 1992-12-07
Arrival Date 1992-12-21
Principal Scientist(s)Alan W Morris (Plymouth Marine Laboratory)
Ship RRS Challenger

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
Q value below limit of quantification