Chemistry

Data & products on marine water quality

How are products generated

Data product generation is the last step of a process made up of several phases, which imply multiple validation steps through a commonly agreed and standardized Quality Control (QC) loop. Within EMODnet Chemistry, commonly agreed and standardized data QC protocols have been defined to guarantee consistency among comprehensive databases, which include data from different sources, periods and geographic areas.

As a result, regional harmonized and validated data collections (buffers) are archived with a quality flag that provides information about data reliability. Regional buffers are used to generate two different kinds of visualization products: climatological maps and dynamic plots.

Climatological maps of selected parameters concentrations related to eutrophication and ocean acidification, are produced from regional validated data collections. Spatially interpolated maps are currently produced as averages over a 10 years moving window in order to find a balance between the duration of the environmental assessment cycle for MSFD (6 years) and the number of years that guarantee a sufficient data coverage. Guidelines for data products generation have been implemented to provide a set of common rules to obtain homogeneous visualization products for all European seas. Interpolated maps are obtained with Data-Interpolating Variational Analysis (DIVA). DIVA interpolation method provides gridded fields by minimising a cost function that takes into account the observations and the regularity of the field. It works internally on a finite element mesh which decouples basins based on topography, can take ocean currents into account, can detect trends in the data, detects and removes outliers and provides a consistent error variance estimation. DIVA software is a powerful instrument and it gives major benefits above standard interpolations. The last release can be cited as: Sylvain Watelet, Charles Troupin, Jean-Marie Beckers, Alexander Barth, & Mohamed Ouberdous. (2017, July 31). gher-ulg/DIVA: v4.7.1 (Version v4.7.1). Zenodo. http://doi.org/10.5281/zenodo.836727

More technical details can be found in:

  • Troupin, C., Barth, A., Sirjacobs, D., Ouberdous, M., Brankart, J.-M., Brasseur, P., Rixen, M., Alvera Azcarate, A., Belounis, M., Capet, A., Lenartz, F., Toussaint, M.-E., & Beckers, J.-M. (2012). Generation of analysis and consistent error fields using the Data Interpolating Variational Analysis (Diva). Ocean Modelling, 52-53, 90-101. doi:10.1016/j.ocemod.2012.05.002
  • Barth, A., Buga, L., Fyrberg, L., Gatti, J., Giorgetti, A., Giorgi, G., Iona, S., Larsen, M., Lipizer, M., Schaap D., Schlitzer, R., Vinci, M., Watelet, S., Wenzer, M., 2015. EMODnet Thematic Lot n° 4 – Chemistry - Methodology for data QA/QC and DIVA products. doi: 10.6092/9f75ad8a-ca32-4a72-bf69-167119b2cc12
  • Barth, A., Watelet, S., Troupin, C., Alvera-Azcárate, A., Beckers, J.-M, 2017. Oceanographic and Marine Cross-Domain Data Management for Sustainable Development, chapter Analysis of ocean in Situ observations and Web-Based Visualization: From Individual Measurements to an Integrated View. IGI Global, Hershey, PA, 345–371. doi: 10.4018/978-1-5225-0700-0

For selected groups of parameters gathered by EMODnet Chemistry, the distribution of sampling stations provides access to dynamic plots (time series or vertical profiles), that are automatically generated from the data available in the regional validated data collections, by a service based on Web Processing Service (WPS) OGC standard, and can be dynamically customized.

The data products, both DIVA basin maps and the validated data collections, are ingested in dedicated viewing service (OceanBrowser), available at Products Viewer and Access Service. Hence users can browse for and visualise selected parameters maps at basin scales of observation densities, (animated) maps of temporal and spatial evolution (also in depth) and plots of temporal and depth variability of monitoring points. Both the generated interpolated maps and the harmonized validated data collections are published in the Data products catalogue, where also detailed descriptions can be found.