Marine Data Quality Flags

From Ocean Teacher Library

Background

Summary tables for quality control flags used in datasets to indicate the assumed quality levels of measurements. Various programs and data management offices have developed different systems, requiring specific conversion protocols (also included) to be developed. Codes can apply to individual measurements or to entire stations.

Quality Flag Tables

In all these systems, "QC" refers to quality control procedures.

Argo

0 - No QC was performed
1 - Good data
2 - Probably good data
3 - Probably bad data that are potentially correctable
4 - Bad data
5 - Value changed
8 - Interpolated value
9 - Missing value

British Oceanographic Data Centre (BODC)

Field left blank - Acceptable value
< - 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
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 - Improbably value, BODC quality control
N - Null value

European Sea Level Service (ESEAS)

0 - No quality control
1 - Correct value
2 - Interpolated value
3 - Doubtful value
4 - Isolated spike or wrong value
5 - Correct but extreme value
6 - Reference change detected
7 - Constant values for more than a defined time interval
8 - Out of range
9 - Missing value

Global Temperature and Salinity Profile Program (GTSPP)

0 - No QC was performed
1 - QC was performed; good data
2 - QC was performed; probably good data
3 - QC was performed; probably bad data
4 - QC was performed; bad data
5 - The value was changed as a result of QC
9 - The value is missing

Ocean Data View Software

0 - Good quality
1 - Unknown quality
4 - Questionable quality
8 - Bad quality

PANGAEA

Left blank - Valid
? - Questionable
/ - Not valid
* - Unknown
# - Individual definition
> - Larger than
< - Less than

Quality Assurance of Real-Time Oceanographic Data (QARTOD)

0 - Quality not evaluated
1 - Bad
2 - Questionable/suspect
3 - Good
9 - Missing data

SeaDataNet

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

Swedish Meteorological and Hydrological Institute (SMHI)

Left blank - Good value
! - Extreme/suspicious value, checked manually and compared with other relevant parameters and found correct
? - Questionable value
B - Bad value
< - Below detection limit/less than
> - Above detection limit/greater than
| - Manually interpolated/extrapolated
C - Value from CTD temp/salin/fluor/oxyg
Z - Zero by definition

WOCE CTD

1 - Not calibrated
2 - Acceptable measurement
3 - Questionable measurement
4 - Bad Measurement
5 - Not reported
6 - Interpolated over >2 dbar level
7 - Despiked
9 - Not sampled

WOCE Bottle Samples

1 - Sample for this measurement was drawn from water bottle but not received
2 - Acceptable measurement
3 - Questionable measurement
4 - Bad Measurement
5 - Not reported
6 - Mean of replicate measurements
7 - Manual chromatographic peak measurement
8 - Irregular digital chromatographic peak integration
9 - Sample not drawn for this measurement from this bottle

World Ocean Database (Individual Observed Parameters)

0 - Accepted value
1 - Range outlier (outside of broad range check)
2 - Failed inversion check
3 - Failed gradient check
4 - Failed observed level "bull's-eye" check or zero-gradient check
- This revised wording confirmed with the US NODC OCL, 2009-07-13
5 - Failed combined gradient and inversion checks
- This revised wording confirmed with the US NODC OCL, 2009-07-13
6 - Failed range and inversion checks
7 - Failed range and gradient checks
8 - Failed range and questionable data checks
9 - Failed range and combined gradient and inversion checks

World Ocean Database (Depths)

0 - Accepted value
1 - Duplicates or inversions in recorded depth (same or less than previous depth)
2 - Density inversion

World Ocean Database (Entire Stations)

0 - Accepted station
1 - Failed annual standard deviation check
2 - Two or more density inversions (Levitus, 1982 criteria)
3 - Flagged cruise
4 - Failed seasonal standard deviation check
5 - Failed monthly standard deviation check
6 - Failed annual and seasonal standard deviation check
7 - Bull's-eye from standard level data or failed annual and monthly standard deviation check
8 - Failed seasonal and monthly standard deviation check
9 - Failed annual, seasonal, and monthly standard deviation check

Crosswalks Between Quality Flag Tables

The most comprehensive crosswalk set for major quality flag systems is provided by the Ocean Data View Quality Flag Schema document. The fourteen major systems (quoted above from the same document) are displayed along with explicit crosswalks between them.

Subsections of this Article

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Information about this article

Short title: Quality Flags

Description: Numeric "tags" applied to datasets, as well as individual data, reflecting objective (and sometimes also expert subjective) evaluations of the "correctness" of the data.

Expertise level: beginner

Author: Murray.Brown

Approval status: approved

Approved by: Murray.Brown

Last change: 2009-9-2

Subsection of: Marine Data Concepts, Marine Data Quality Control

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