SeaDataNet standards for quality control. Lesley Rickards, BODC and all SeaDataNet partners

Transcription

1 SeaDataNet standards for quality control Lesley Rickards, BODC and all SeaDataNet partners

2 SeaDataNet standards for quality control Good quality research depends on good quality data Good quality data depends on good quality control methods Quality control includes: Basic automatic checks which can be applied to almost all data types (e.g. biological, chemical, physical and geological/geophysical data), often in near-real-time A more scientific level of quality control carried out tailored to the type of data, often including visual inspection Data can be considered trustworthy after thorough processing methods have been carried out At this stage they can be incorporated into databases or distributed to users via national or international exchange

3 SeaDataNet standards for quality control Data quality control has the following objective: To ensure the data consistency within a single data set and within a collection of data sets and to ensure that the quality and errors of the data are apparent to the user who has sufficient information to assess its suitability for a task. (IOC/CEC Manual, 1993) Quality control, if done well, brings about a number of key advantages: Maintaining standards Consistency Reliability

4 SeaDataNet standards for quality control IODE/JCOMM Forum on Oceanographic Data Management and Exchange Standards Date and time: recommended to adopt the ISO standard (using extended format) where appropriate while recognising some limitations Latitude, longitude, altitude: recommended to adopt the ISO-6709 standard Countries: recommended to adopt the ISO-3166 ( and ) standard Reference: Intergovernmental Oceanographic Commission 2008 IODE/JCOMM Forum on Oceanographic Data Management and Exchange Standards, IOC Project Office for IODE, Oostende, Blegium January Oostende, Belgium: IOC/IODE Project Office, 45pp. (IOC Workshop Report No. 206) (English)

5 SeaDataNet standards for quality control Outcomes of Standards Forum relevant to QC No recommended standards identified, but: Temperature and salinity profiles: GTSPP to revise IOC Manuals and Guides No. 22 Surface T&S: GOSUD to revise their QC document Sea level: revise ESEAS QC document in close collaboration with the GE-GLOSS Currents: consolidate input from US IOOS with IOC Manuals and Guides No. 26; add info on HF radar Surface waves: update IOC Manuals and Guides No. 26; US IOOS will provide the US national waves plan SeaDataNet QC flags are a sensible extension to handle situations appropriate for a greater range of variables Developed Guidelines for a Manual on Quality Control document

6 SeaDataNet standards for quality control REFERENCES NODC procedures (e.g. France, Greece, Italy, Norway, Spain, Sweden, UK) EU MEDAR-MEDATLAS procedures and SCOOP software EU SIMORC project (Met-ocean data QC) EU ESEAS (sea level) and IOC GLOSS documents Manual of Quality Control Procedures for Validation of Oceanographic Data, UNESCO, IOC - Manuals & Guides, 1993, Manual And Guides 26 GTSPP QC (IOC Manuals and Guides No. 22) Argo Quality Control Manual (Real Time and Delayed Mode) GOSUD Real-time quality control IODE s OceanTeacher ICES WG Marine Data Management Data Type Guidelines JPOTS Manual, 1991 WOCE manuals JGOFS Protocols World Ocean Database Quality Control documentation TOGA/COARE Handbook of Quality Control Procedures for Surface Meteorology Data BODC-WOCE Sea Level Data Assembly Centre Quality Assessment AODC Quality Control Cookbook for XBT Data Chapman, A. D Principles and Methods of Data Cleaning Primary Species and Species- Occurrence Data, version 1.0. Chapman, A. D Principles of Data Quality, version 1.0. Report for the Global Biodiversity Information Facility, Copenhagen. Ocean biodiversity informatics : a new era in marine biology research and management (Mark J. Costello, Edward Vanden Berghe) QARTOD (Quality Assurance of Real-Time Oceanographic Data)

7 SeaDataNet standards for quality control Recent developments: Memorandum of Understanding between SeaDataNet and MyOcean in situ TAC including collaboration on quality control Output from the First IODE Workshop on Quality Control of Chemical Oceanographic Data Collections GeoSeas for marine geology/geophysics Other QC presentations and posters here at IMDIS2010

8 SeaDataNet standards for quality control For all types of data information is required about: Where the data were collected: location (preferably as latitude and longitude) and depth/height When the data were collected (date and time in UTC or clearly specified local time zone) How the data were collected (e.g. sampling methods, instrument types, analytical techniques) How the data are referenced (e.g. station numbers, cast numbers) Who collected the data, including name and institution of the data originator(s) and the principal investigator What has been done to the data (e.g. details of processing and calibrations applied, algorithms used to compute derived parameters) Comments for other users of the data (e.g. problems encountered and comments on data quality)

9 SeaDataNet standards for quality control Parameter Details Parameters measured (Refer to BODC Parameter Usage Vocabulary if necessary for help with parameter definitions) Data Processing Details Originator's Data Format Description of calibrations Description of any data processing that has occurred (manufacturers and in-house)

10 AUTOMATIC QUALITY CONTROL CHECKS

11 Basic automatic checks for all data types Date and time of an observation has to be valid Year 4 digits Month between 1 and 12 Day in range expected for month Hour between 0 and 23 Minute between 0 and 59 Latitude and longitude have to be valid Latitude in range -90 to 90 Longitude in range -180 to 180 Position must not be on land Observation latitude and longitude located in ocean For example, use 5-minute bathymetry (e.g. ETOPO5)

12 Further automatic checks Impossible speed Tests for acceptable speed between stations Spike Tests salinity and temperature data for large differences between adjacent values (many other parameters also) Gradient Tests for gradient between vertically adjacent salinity and temperature measurements too steep Density inversion Tests where calculated density at a higher pressure in a profile is less than the calculated density at an adjacent lower pressure Pressure increasing Pressures from the profile monotonically increasing

13 Further automatic checks Global range Tests that observed temperature and salinity values are within the expected extremes encountered in the oceans (many other parameters also) Regional range Tests that observed temperature and salinity values are within the expected extremes encountered in particular regions (many other parameters also) Deepest pressure Tests that profile does not contain pressures higher than the highest value expected Check for duplicates Cruises or stations within a cruise using a space-time radius (e.g., for duplicate cruises: 1 mile, 15min or 1day if time is unknown)

14 SCIENTIFIC QUALITY CONTROL CHECKS

15 SeaDataNet standards for quality control Visual inspection of data Pressure/depth series (e.g. CTD) Property-property plot Time series (e.g. current meter, sea level) Scatter plot (e.g. current meter) Map covering the locations of series Ensure that data are free from instrumentgenerated spikes, gaps, spurious data at the start and end of the record and other irregularities Apply quality flags Quality flags do not change the data Visual inspection can be subjective, dependent on experience

16 SeaDataNet standards for quality control Spike detection Can require visual inspection to back up automatic check Range check Comparison with pre-existing climatological statistics Compare data collected on same cruise and in same area

17 SeaDataNet standards for quality control BELOW: example of a record with suspect directions ABOVE: example of a good scatter plot

18 SeaDataNet standards for quality control Scatter plot of wave height against (zero up-crossing or crest) period Wave heights (maximum in pink; significant in blue) are ok for range, basically normal distribution, steepness (all < 5%)

19 SeaDataNet standards for quality control Sea Level Data GLOSS QC manual Harmonic analysis - generate predictions Calculate residuals Spikes Constant values Clock malfunctions Gap filling Reference changes Calculation of statistics

20 SeaDataNet standards for quality control Discrete Water Sample Data How trace values (values below the detection limit) identified What is the precision of the methods (e.g. number of significant figures) What analyses performed (use parameters descriptions as described in the ICES green book) What units are used Duplicate samples taken? Comments describing each station Supply calibration document Station number, site details, sample identifier (or bottle number), type of station, continuous flow etc., Check profiles vs. regional climatology Check calibration information available Compare parameters for predictable relationships (e.g. parameter ratios)

21 SeaDataNet standards for quality control Biological data quality control Not straightforward... Guided by: Chapman, A. D Principles and Methods of Data Cleaning Primary Species and Species-Occurrence Data, version 1.0. Chapman, A. D Principles of Data Quality, version 1.0. Report for the Global Biodiversity Information Facility, Copenhagen. O Brien, T.D COPEPOD: A Global Plankton Database. U.S. Dep. Commerce, NOAA Tech. Memo. NMFS-F/SPO-73, 136 p. ICES Data Type Guidelines IOC/IODE GE-BICH

22 SeaDataNet standards for quality control SeaDataNet quality control flags (L201) Flag Short description 0 No quality control 1 The value appears to be correct 2 The value appears to be probably good 3 The value appears probably bad 4 The value appears erroneous 5 The value has been changed 6 Below detection limit 7 In excess of quoted value 8 Interpolated value 9 Missing value A Incomplete information Based on IGOSS/UOT/GTSPP & Argo quality flags

23 SeaDataNet standards for quality control Summary Quality control, if done well, brings about a number of key advantages: maintains standards, consistency, reliability Use automatic and more scientific QC Much information out there; many standards, we need to converge Use IODE/JCOMM oceanographic data standards process Need to review regularly and cover new data types All data sets need to be fully documented to ensure they can be used in the future without ambiguity or uncertainty