Metadata Report for BODC Series Reference Number 1172722


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Sea-Bird SBE 911plus CTD  CTD; water temperature sensor; salinity sensor
Sea-Bird SBE 3plus (SBE 3P) temperature sensor  water temperature sensor
Sea-Bird SBE 4C conductivity sensor  salinity sensor
Instrument Mounting lowered unmanned submersible
Originating Country United Kingdom
Originator Dr John Huthnance
Originating Organization Proudman Oceanographic Laboratory (now National Oceanography Centre, Liverpool)
Processing Status banked
Project(s) Oceans 2025
Oceans 2025 Theme 3
Oceans 2025 Theme 3 WP3.1
Geophysical Oceanography
 

Data Identifiers

Originator's Identifier D318_CTD007
BODC Series Reference 1172722
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2007-05-01 05:44
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 1.0 metres
 

Spatial Co-ordinates

Latitude 36.07955 N ( 36° 4.8' N )
Longitude 9.55565 W ( 9° 33.3' W )
Positional Uncertainty 0.01 to 0.05 n.miles
Minimum Sensor Depth 15.0 m
Maximum Sensor Depth 3993.0 m
Minimum Sensor Height 100.0 m
Maximum Sensor Height 4078.0 m
Sea Floor Depth 4093.0 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 Approximate - Depth is only approximate
 

Parameters

BODC CODE Rank Units Short Title Title
ACYCAA01 1 Dimensionless Record_No Sequence number
DEPHPR01 1 Metres CmpDep Depth below surface of the water body by profiling pressure sensor and converted to seawater depth using UNESCO algorithm
POTMCV01 1 Degrees Celsius WC_Potemp Potential temperature of the water body by computation using UNESCO 1983 algorithm
PSALST01 1 Dimensionless P_sal_CTD Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm
SIGTPR01 1 Kilograms per cubic metre SigTheta Sigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO 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

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

Sea-Bird Electronics SBE 911 and SBE 917 series CTD profilers

The SBE 911 and SBE 917 series of conductivity-temperature-depth (CTD) units are used to collect hydrographic profiles, including temperature, conductivity and pressure as standard. Each profiler consists of an underwater unit and deck unit or SEARAM. Auxiliary sensors, such as fluorometers, dissolved oxygen sensors and transmissometers, and carousel water samplers are commonly added to the underwater unit.

Underwater unit

The CTD underwater unit (SBE 9 or SBE 9 plus ) comprises a protective cage (usually with a carousel water sampler), including a main pressure housing containing power supplies, acquisition electronics, telemetry circuitry, and a suite of modular sensors. The original SBE 9 incorporated Sea-Bird's standard modular SBE 3 temperature sensor and SBE 4 conductivity sensor, and a Paroscientific Digiquartz pressure sensor. The conductivity cell was connected to a pump-fed plastic tubing circuit that could include auxiliary sensors. Each SBE 9 unit was custom built to individual specification. The SBE 9 was replaced in 1997 by an off-the-shelf version, termed the SBE 9 plus , that incorporated the SBE 3 plus (or SBE 3P) temperature sensor, SBE 4C conductivity sensor and a Paroscientific Digiquartz pressure sensor. Sensors could be connected to a pump-fed plastic tubing circuit or stand-alone.

Temperature, conductivity and pressure sensors

The conductivity, temperature, and pressure sensors supplied with Sea-Bird CTD systems have outputs in the form of variable frequencies, which are measured using high-speed parallel counters. The resulting count totals are converted to numeric representations of the original frequencies, which bear a direct relationship to temperature, conductivity or pressure. Sampling frequencies for these sensors are typically set at 24 Hz.

The temperature sensing element is a glass-coated thermistor bead, pressure-protected inside a stainless steel tube, while the conductivity sensing element is a cylindrical, flow-through, borosilicate glass cell with three internal platinum electrodes. Thermistor resistance or conductivity cell resistance, respectively, is the controlling element in an optimized Wien Bridge oscillator circuit, which produces a frequency output that can be converted to a temperature or conductivity reading. These sensors are available with depth ratings of 6800 m (aluminium housing) or 10500 m (titanium housing). The Paroscientific Digiquartz pressure sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

Additional sensors

Optional sensors for dissolved oxygen, pH, light transmission, fluorescence and others do not require the very high levels of resolution needed in the primary CTD channels, nor do these sensors generally offer variable frequency outputs. Accordingly, signals from the auxiliary sensors are acquired using a conventional voltage-input multiplexed A/D converter (optional). Some Sea-Bird CTDs use a strain gauge pressure sensor (Senso-Metrics) in which case their pressure output data is in the same form as that from the auxiliary sensors as described above.

Deck unit or SEARAM

Each underwater unit is connected to a power supply and data logging system: the SBE 11 (or SBE 11 plus ) deck unit allows real-time interfacing between the deck and the underwater unit via a conductive wire, while the submersible SBE 17 (or SBE 17 plus ) SEARAM plugs directly into the underwater unit and data are downloaded on recovery of the CTD. The combination of SBE 9 and SBE 17 or SBE 11 are termed SBE 917 or SBE 911, respectively, while the combinations of SBE 9 plus and SBE 17 plus or SBE 11 plus are termed SBE 917 plus or SBE 911 plus .

Specifications

Specifications for the SBE 9 plus underwater unit are listed below:

Parameter Range Initial accuracy Resolution at 24 Hz Response time
Temperature -5 to 35°C 0.001°C 0.0002°C 0.065 sec
Conductivity 0 to 7 S m -1 0.0003 S m -1 0.00004 S m -1 0.065 sec (pumped)
Pressure 0 to full scale (1400, 2000, 4200, 6800 or 10500 m) 0.015% of full scale 0.001% of full scale 0.015 sec

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

BODC CTD Screening

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 that cannot be resolved.

Data cycles are inspected using depth series plots of all parameters. These presentations undergo screening to detect infeasible values within the data cycles themselves and inconsistencies when comparing 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 following types of irregularity, each relying on visual detection in the time series plot, are amongst those that may be flagged as suspect:

If a large percentage of the data is affected by irregularities, deemed abnormal, then instead of flagging the individual suspect values, a caution may be documented.

The following types of inconsistency are detected automatically by software:

Inconsistencies between the characteristics of the data set and those of its neighbours are sought, and where necessary, documented. This covers inconsistencies in the following:

This 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's making are not introduced.

Instrument description document for D318 CTD

CTD unit and auxiliary sensors

The CTD unit comprised a Sea-Bird Electronics (SBE) 9 plus underwater unit, an SBE 11 plus deck unit and an SBE 32 carousel 24 - position system; all of which were mounted on a National Marine Facilities (NMF) 24 way stainless steel frame. 10L Niskin bottles were attached to 12 of the carousel's 24 available rosette positions. These were attached in alternate positions on the rosette, with only the odd rosette positions being used. One SBE Digiquartz pressure sensor, two SBE 3P temperature sensors and two SBE 4C conductivity sensors were attached to the CTD. Three of the auxiliary voltage channels were used. Attached to these channels were an SBE 43 dissolved oxygen sensor, a Benthos Sonar Altimeter and a Chelsea Alphatracka MKII. Also attached to the SBE 9 plus was an NMF 10 kHz pinger, which was used as a backup to the Benthos PSA and as a double-check on the proximity of the CTD to the seabed. The pressure sensor was located 34 cm below the bottom of the Niskin bottles, and 124 cm below the top of the Niskin bottles.

In addition to the sensors mentioned above, three stand-alone instruments were attached to the CTD. For both legs of the cruise an RDI Workhorse 300 kHz Lowered ADCP (downwards looking master) and an RDI Broadband 150 kHz Lowered ADCP (downwards looking slave) were attached to the main CTD unit. A Valeport MIDAS SVP 6000DB Sound Velocity Probe was also attached for the first leg (D318a), however this was removed for D318b. These instruments recorded their data internally, thus their data are not available in the CTD data files and their specifications have not been included in the table below.

Sensor unit Model Serial number Full specification Calibration dates (YYYY/MM/DD) Comments
CTD underwater unit SBE 9 plus 09p-24680-0636 SBE 9 plus - -
CTD deck unit SBE 11 plus 11p-24680-0588 - - -
Carousel SBE 32 - 24 Position Pylon 32-37898-0518 SBE 32 - -
Pressure sensor SBE plus Digiquartz 83008 - 2005-05-13 -
Temperature sensor SBE 3P 03P-4151 SBE 03P 2006-11-07 This sensor supplied primary temperature. Due to spiking in primary temperature, only secondary temperature and salinity were supplied to BODC
Temperature sensor SBE 3P 03P-4105 - 2006-11-07 This sensor supplied secondary temperature
Conductivity senor SBE 4C 04C-2231 SBE 04C 2007-01-09 This sensor provided primary conductivity. Due to spiking in primary temperature, only secondary temperature and salinity were supplied to BODC
Conductivity sensor SBE 4C 04C-2841 - 2007-01-26 This sensor supplied secondary conductivity.
Dissolved oxygen sensor SBE 43 43B-0619 SBE 43 2006-10-05 The originator did not supply BODC with these data as it was not used in their analysis.
Altimeter Benthos PSA 916T 1040 Benthos Altimeter Repaired, December 2006 The originator did not supply BODC with these data as it was not used in their analysis.
Transmissometer Chelsea MKII Alphatracka - 25 cm path 161-2642-002 Alphatracka MKII 1996-09-04 The originator did not supply BODC with these data as it was not used in their analysis.

Originator's processing document for D318 CTD data

Sampling strategy

A total of eight CTD casts were performed during the RSS Discovery cruise D318 which took place in the Gulf of Cadiz (for more information see the D318 cruise report ). The cruise was split into two legs; D318a which took place from 17 April 2007 to 23 April 2007 and D318b which was conducted between 27 April 2007 and 14 May 2007. Five CTD casts were performed on the D318a leg, with the remaining three being performed on the D318b leg. The casts conducted during D318a number from cast 001-004a. Cast 004a was a performed as a repeat of cast 004, which was aborted so that the research crew could attempt to solve a spiking issue, which had been affecting the primary temperature sensor since cast002. This attempt was unsuccessful, however between D318a and D318b the cable connecting the temperature sensor was replaced, which fixed the problem for the casts performed during D318b (casts 005-007).

The casts undertaken during D318a were performed in conjunction with the deployment of moorings at sites located on the edge of the continental shelf. For the second leg the RSS Discovery was joined by the RV Poseidon. Casts 005-007 were performed in deeper water, as repeats of casts undertaken by the RV Poseidon, whose CTD cable was limited to depths of 2,000 m. During most casts the CTD profiles stretched from the surface to approximately five metres from the bottom. This was changed to 25 m above the seabed in cast 004a, due to the excessive CTD wire angles observed. There was no requirement for the science party to work so close to the bottom during cast 007, so the downcast was halted approximately 100 m from the sea bed. A total of 42 water bottle samples were taken during the cruise for the calibration of salinity samples. Samples were taken on all casts apart from the aborted cast 004.

Data Processing

The initial post cruise processing was carried out by National Marine Facilities (NMF) using the SeaBird Electronics SeaSoft data processing software (version 5.35). The raw (.dat) files were converted from binary to engineering units and ASCII (.cnv) files using the DATCNV program. SeaBird rosette data files (.ros), which contain five second scan ranges centered on the bottle firing times, were also generated during this process. ALIGNCTD was run to advance the oxygen four seconds, compensating for a time lag in the dissolved oxygen sensor. CELLTM was run using alpha = 0.03 and 1/beta = 7, to correct for conductivity errors induced by the transfer of heat from the conductivity cell to the seawater.

Five second bottle summaries comprising the data recorded during each bottle firing were produced by running BOTTLESUM. The DERIVE program was used to calculate salinity, sigma-theta, potential temperature, oxygen saturation and Chen-Millero sound velocities. Finally ASCIIOUT was run to export the data in 24 Hz ASCII format and SEAPLOT was used on the derived files to generate graphs (.wmf) of secondary temperature, salinity, density and sound velocity on the same 0-4000 metre scale.

Once the initial processing had been completed, further processing was carried out at the Proudman Oceanographic Laboratory (POL) by the data originator. All the channels were dropped apart from Julian day, pressure, depth, temperature and salinity. These were the only channels present in the final version of the dataset provided to BODC. Secondary temperature and salinity were provided instead of data from the primary sensors, due to the spiking in primary temperature which was observed during casts 002-004a. Previous attempts by NMF to solve this problem using WILDEDIT had proved unsuccessful. Finally, the upcast and surface soak were removed, and the data were processed into one metre depth bins, by the data originator.

Field Calibrations

Salinity

42 salinity samples were collected for the salinity calibrations. Six samples were collected from six depths during each CTD cast, except the aborted cast 004 which collected no salinity samples. The bottle samples were analysed using a Guildline Autosal 8400B salinometer (s/n 60839). The salinometer was operated in the constant temperature (CT) lab with a bath temperature of 24 °C. The ambient room temperature of the CT lab was 22-22.5°C. The temperature stability in the CT lab was very good and yielded trouble free salinometry. The CTD samples were taken and run using a Softsal PC by NMF. All samples were processed according to World Ocean Circulation Experiment (WOCE) standards and protocols. The calibration equation used for secondary salinity has been provided below.

Autosal salinity = (0.997908 x CTD secondary salinity) + 0.075656

R 2 = 0.999982

Pressure

While the CTD was sat on deck, the average reading from the pressure sensor was 1.2 dbar. Therefore, the pressure channel has had a 1.2 dbar offset applied to it by the data originator. Depth readings from the CTD also take this offset into account.

Processing of D318 CTD data by BODC

BODC received eight ASCII format CTD series, which were the seven completed casts plus the aborted cast 004. Only the downcast was provided and the Originator had binned the data at one metre intervals. In addition to these files, BODC have also received the post-cruise backup of these data from National Marine Facilities (NMF), which consisted of raw and processed versions of the data as well as some supplementary information. These data have not been processed by BODC but are available on request. Following standard BODC procedure, the binned data files were processed and reformatted to BODC internal format. The aborted cast was also transferred because communications with the Originator and inspection of the data revealed that the series contained usable data. The table below shows how the variables within the processed data files were mapped to appropriate BODC parameter codes.

Originator's variable Units Description BODC parameter code Units Comments
Days Julian days - - - This variable was not transferred. BODC re-calculate date and time when the data is transferred
Pressure db - - - This variable was not transferred as Originator processed data into one metre depth bins
Depth m Depth below surface of the water body by profiling pressure sensor and converted to seawater depth using UNESCO algorithm DEPHPR01 Metres -
Temperature °C Temperature of the water body by CTD or STD TEMPST01 °C -
Salinity PSU Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm PSALST01 Dimensionless -
- - Sigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm SIGTPR01 kg -1 m -3 Derived by BODC from TEMPST01, PSALST01 and PRESPR01 following Fofonoff and Millard (1982)
- - Potential temperature of the water body by computation using UNESCO 1983 algorithm POTMCV01 °C Derived from TEMPST01, PSALST01 and PRESPR01 following Fofonoff and Millard (1982)

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, missing data by both setting the data to an appropriate value and setting the quality control flag.

References

Fofonoff, NP and Millard, RC. 1983. Algorithms for computations of fundamental properties of seawater. UNESCO Technical Papers in Marine Science, 44, p.53.


Project Information

Oceans 2025 - The NERC Marine Centres' Strategic Research Programme 2007-2012

Who funds the programme?

The Natural Environment Research Council (NERC) funds the Oceans 2025 programme, which was originally planned in the context of NERC's 2002-2007 strategy and later realigned to NERC's subsequent strategy (Next Generation Science for Planet Earth; NERC 2007).

Who is involved in the programme?

The Oceans 2025 programme was designed by and is to be implemented through seven leading UK marine centres. The marine centres work together in coordination and are also supported by cooperation and input from government bodies, universities and other partners. The seven marine centres are:

Oceans2025 provides funding to three national marine facilities, which provide services to the wider UK marine community, in addition to the Oceans 2025 community. These facilities are:

The NERC-run Strategic Ocean Funding Initiative (SOFI) provides additional support to the programme by funding additional research projects and studentships that closely complement the Oceans 2025 programme, primarily through universities.

What is the programme about?

Oceans 2025 sets out to address some key challenges that face the UK as a result of a changing marine environment. The research funded through the programme sets out to increase understanding of the size, nature and impacts of these changes, with the aim to:

In order to address these aims there are nine science themes supported by the Oceans 2025 programme:

In the original programme proposal there was a theme on health and human impacts (Theme 7). The elements of this Theme have subsequently been included in Themes 3 and 9.

When is the programme active?

The programme started in April 2007 with funding for 5 years.

Brief summary of the programme fieldwork/data

Programme fieldwork and data collection are to be achieved through:

The data is to be fed into models for validation and future projections. Greater detail can be found in the Theme documents.


Oceans 2025 Theme 3: Shelf and Coastal Processes

Over the next 20 years, UK local marine environments are predicted to experience ever-increasing rates of change - including increased temperature and seawater acidity, changing freshwater run-off, changes in sea level, and a likely increase in flooding events - causing great concern for those charged with their management and protection. The future quality, health and sustainability of UK marine waters require improved appreciation of the complex interactions that occur not only within the coastal and shelf environment, but also between the environment and human actions. This knowledge must primarily be provided by whole-system operational numerical models, able to provide reliable predictions of short and long-term system responses to change.

However, such tools are only viable if scientists understand the underlying processes they are attempting to model and can interpret the resulting data. Many fundamental processes in shelf edge, shelf, coastal and estuarine systems, particularly across key interfaces in the environment, are not fully understood.

Theme 3 addresses the following broad questions:

Within Oceans 2025, Theme 3 will develop the necessary understanding of interacting processes to enable the consequences of environmental and anthropogenic change on UK shelf seas, coasts and estuaries to be predicted. Theme 3 will also provide knowledge that can improve the forecasting capability of models being used for the operational management of human activities in the coastal marine environment. Theme 3 is therefore directly relevant to all three of NERC's current strategic priorities; Earth's Life-Support Systems, Climate Change, and Sustainable Economies

The official Oceans 2025 documentation for this Theme is available from the following link: Oceans 2025 Theme 3

Weblink: http://www.oceans2025.org/


Oceans 2025 Theme 3, Work Package 3.1: Global Impacts of Shelf Seas

At the margins of the shelf seas, steep shelf-slope bathymetry has impacts on ocean circulation and the transmission of signals around the ocean basins (Hughes and Meredith, 2006), while dense water formation and cascades at the shelf edge are thought to be important for water mass formation (Ivanov et al., 2004) and for the off-shelf transport of organic and inorganic carbon (e.g. Wollast and Chou, 2001).

In this Work Package, the Proudman Oceanographic Laboratory (POL) aim to quantify the water fluxes between the shelf and open ocean globally, including the development of methods to incorporate shelf effects into global models. Greater understanding of the whole carbon cycle will benefit from combining this work on down-slope fluxes of water (and its constituent dissolved carbon) with work in Oceans 2025 Theme 5 (down-slope transports of sediments and particulate carbon).

The specific objectives are:

More detailed information on this Work Package is available at pages 5 - 27 of the official Oceans 2025 Theme 3 document: Oceans 2025 Theme 3

Weblink: http://www.oceans2025.org/

Some data used in Work Package 3.1 were collected to complement work carried out on the European Union's Geophysical Oceanography (GO) project. For these data, linkage to the GO project documentation is provided

References:

Hughes CW. and Meredith MP., 2006. Coherent sea level fluctuations along the global continental slope. Phil Trans Roy Soc A, 364, 885-901.

Ivanov VV., Shapiro GI., Huthnance JM., Aleynik DL. and Golovin PN., 2004. Cascades of dense water around the world ocean. Progr in Oceanogr, 60(1), 47-98.

Wollast R. and Chou L., 2001. Ocean margin exchange in the northern Gulf of Biscay: OMEX I. An introduction. Deep Sea Res II 48, 2971-2978.

Yool A. and Fasham MJR., 2001. An examination of the 'continental shelf pump' in an open ocean general circulation model. Global Biogeochem Cycles, 15, 831-844.


Geophysical Oceanography

This project was funded by the European Union (EU) as part of Framework 6 - New and Emerging Science and Technologies (NEST) programme. The project ran from 01 February 2006 to 30 September 2009. There were eight scientific institutions involved in the project:

Research aims

The primary aims of Geophysical Oceanography (GO) project were to provide a calibration between seismic images of water structure and conventional oceanographic measurements, in addition to testing various seismic acquisition systems and novel geometries for seismic imaging of water structure. In particular, this project examined internal waves and their interaction with the continental slope, while using extensive marine geophysical knowledge acquired over the past 4 decades to evaluate longer term changes in the ocean structure.

Fieldwork

Research for GO was conducted during RSS Discovery cruise D318, which was split into two legs, D318a and D318b. The research was conducted between 17 April 2007 and 14 May 2007 in the Gulf of Cadiz. For leg D318b, RSS Discovery was joined by RV Poseidon cruise PO350 (funded under a separate grant from the German research council with project partners IFM-GEOMAR). Some of the fieldwork provided data for Natural Environment Research Council (NERC) Oceans 2025 Theme 3 Work Package 3.1 as well as for GO. These data have been tagged accordingly below.

GO fieldwork objectives

The primary objectives of the GO project were:

The main objectives of cruise D318 were:

The main objective of cruise PO350 was:

D318 measurements

PO350 measurements


Data Activity or Cruise Information

Cruise

Cruise Name D318B
Departure Date 2007-04-27
Arrival Date 2007-05-14
Principal Scientist(s)Richard W Hobbs (University of Durham, Department of Earth Sciences)
Ship RRS Discovery

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