Bathymetry

EMODnet-Bathymetry provides a service for viewing and downloading a harmonised Digital Terrain Model (DTM) for the European sea regions. The DTM is generated by the EMODnet Bathymetry partnership. Services for discovery and requesting access to these data sets are provided as well.

Objectives

EMODnet Bathymetry aims to provide a single access point to bathymetric data (survey data sets and composite DTMs), and derived bathymetric data products such as best-estimate European digital coastlines, inventory of official coastlines and baselines, a series of high-resolution DTMs for selected areas, and the EMODnet Bathymetry World Base Layer OGC web service. Its flagship data product is the harmonised Digital Terrain Model (DTM) for all European sea regions with a common grid resolution which is generated and regularly updated on the basis of an increasing collection of bathymetric data sets, gathered from organisations from government, research institutes, and industry. This DTM is updated every 2 years and made available in the EMODnet Mapviewer, by OGC web services, and by downloading in multiple formats for use in GIS systems and as baselayer for numerical hydraulic models.

Approach

EMODnet Bathymetry is undertaken by a gradually expanding consortium of organisations from marine science, governmental departments, national hydrographic services, and industry. They combine expertises and experiences of collecting, processing, and managing of bathymetric data together with expertises in distributed data infrastructure development and operation and providing OGC services (WMS, WFS, and WCS) for viewing and distribution.

They bring together bathymetric data sets from in-situ surveys, composite DTMs, and Satellite Derived Bathymetry products, which are managed and described in INSPIRE compliant catalogue services, such as the SeaDataNet CDI data discovery and access service for survey data sets and the SeaDataNet Sextant catalogue for composite DTMs.

Moreover, an effective production workflow has been designed and deployed in accordance with international standards for generation and distribution of the EMODnet Digital Terrain Model (DTM) for all European sea regions and for referencing its input data sets. Survey data and Composite DTMs are pre-gridded and pre-processed to the required EMODnet grid, resolution and format by data providers, using the standard GLOBE software. This is followed by Regional Coordinators, each round upgrading Regional DTMs, and each supported by a regional group of data providers. They are responsible for a quality assessment and selection of the data contributions and the compilation of the Regional DTMs, again using GLOBE software. Gaps in data coverage are filled by using the GEBCO bathymetry model, while GEBCO in turn integrates the EMODnet DTM, which benefits both products. The RDTMs and QA-QC reports are forwarded to the integrator for building the overall EMODnet DTM. The integrator also performs a number of quality checks and measures, before making the new DTM release ready for publishing.

With multiple actors (data providers, regional coordinators, web/portal integrator, metadata curators) communication is at the heart of this methodology. Efficient communication is ensured between all these levels, based on commonly agreed concepts, methodologies, documentation, and software tools.

The EMODnet DTM is a major and highly popular data product as it is used for a whole range of applications in marine science, sustainable ocean governance, and blue economy activities such as planning of pipeline trajectories, locations of offshore wind farms or planning of harbour extensions. In science, the DTM supports oceanographers in providing a base geometry for hydrodynamic models, marine geologists for studying dynamic morphological processes, and biologists in contributing to the generation of seabed habitat maps. An improved DTM also contributes to reducing risks for damage to coastal and offshore installations and public safety by improving our ability to forecast storm surges for example.

In addition, to the flagship DTM product, EMODnet Bathymetry also produces and publishes best-estimate European digital coastlines, an inventory of official coastlines and baselines, a series of high-resolution DTMs for selected areas, and the EMODnet Bathymetry World Base Layer OGC web service, again with great attention for quality and involving hydrography experts from all of Europe.

Products overview

Operational data discovery and viewing services for bathymetric data products (DTM layers) are provided to users since June 2011.

Layers/Data products

Users have access to the following geographical information system layers as part of the Mapviewer:

• Mean depth full coverage with water depth to Lowest Astronomical Tide (LAT) reference from EMODnet DTM in gridded form over whole of maritime basin on a grid of 1/16 * 1/16 arc minutes (ca. 115 metre grid) complemented by land DTM and GEBCO coverage in traditional atlas style colours.
• Mean depth in multi-color style with water depth to LAT reference from EMODnet DTM in gridded form over whole of maritime basin on a grid of 1/16 * 1/16 arc minutes (ca. 115 metre grid) complemented by GEBCO coverage but no land.
• Mean depth in rainbow colour style with water depth to LAT reference from EMODnet DTM in gridded form over whole of maritime basin on a grid of 1/16 * 1/16 arc minutes (ca. 115 metre grid) complemented by GEBCO coverage but no land.
• Source references is a layer which allows to identify the prevailing data sources used for each DTM grid cell. Activating the identification function in the sources layer will reveal for each DTM cell which survey data set or composite DTM was used with a link to their metadata from the CDI Data Discovery and Access service or Sextant Catalogue service. Grey areas are derived from GEBCO.
• Quality Index is an improved source reference layer with quality indication. Metadata has been expanded with characterization of the dataset by vertical, horizontal and temporal indicators, purpose of the survey, and information about commonly adopted standards. Analysis has resulted in extra maps with Quality Indicators for each source reference. A report about the Quality Index analysis method and results can be downloaded, while the maps can be viewed and interrogated for metadata.
• High Resolution bathymetry is a multi-resolution layer which allows to view, zoom in, interrogate for metadata, and download of a collection of higher resolution composite DTMs (HR-DTMs) for selected areas. The resolution of HR-DTMs varies between 1/32 and 1/512 arc minutes, depending on local data policy of data providers.
• Survey tracks/polygons iis another layer to view the locations and retrieve (CDI) metadata of the so far collated bathymetric survey data sets. Users can define a latitude(lat)/longitude(lon)box that will jump to the CDI Data Discovery and Access service for retrieving CDI metadata for the survey data sets within that geographical search window. This will then facilitate the users to refine their query and to request access to the high-resolution survey data sets themselves by means of a shopping mechanism.
• Land geography and topography as derived from OpenStreetMap.
• Geographic names on land is a customized layer of geographic names derived from Open Street Map.
• Displayed Coastlines are derived from OpenStreetMap 2020 WMS. It is a highly detailed coastline and a topographic representation. In addition, a dedicated task of EMODnet Bathymetry is to generate best-estimate coastlines (as interpreted from the intersections of know tidal levels and topography). These were determined from satellite data (typically Sentinel-2 and Landsat-8) and in combination with the Global Tide Surge Model (GTSM) processed into digital coastlines for the European seas at LAT (Lowest Astronomical Tide), MSL (Mean-Sea-Level), and MHW (Mean-High-Water). The level of detail is bound to the resolution of the satellite sensor (e.g. 10m for Sentinel-2). A first release was made in 2018, while an update with improvement of methodology and also adding Northern areas was released in December 2020. The latest version now covers the entire coastline of Europe. These satellite derived coastlines can be viewed as extra layer in the Viewing service while a report gives background information.
  Furthermore, an inventory and report were compiled in 2018 and updated in 2020 with official baseline and coastline data as collected from 26 national authorities in Europe. It describes the information available per country, the resolution, the source of the data and the institute providing/ hosting the data. Users can download the latest inventory and shapefiles of the baselines and coastlines.
• Underwater features which is provided by the General Bathymetric Chart of the Oceans (GEBCO) as GEBCO Undersea Features WMS. The GEBCO Sub-Committee on Undersea Features (SCUFN) maintains and provides a gazetteer of the names, generic feature type and geographic positions of features on the seafloor. The level of detail is dependent on the viewing scale.
• Wrecks which is provided by partner OceanWise as proprietary WMS service and uses the UKHO Wrecks database as source. This Wrecks layer covers all European seas and the level of detail is dependent on the viewing scale.
• Geographic map grid.
• EMODnet Bathymetry World Base Layer (EBWBL), generated in 2020, is a WMTS service providing a gridded representation of worldwide bathymetric and topographic coverage adapted for a better representation of seabed morphological features. It is composed of the 2018 EMODnet Bathymetric grid around Europe (approx. 115m resolution) and uses the GEBCO 2019 grid (approx. 500m resolution) elsewhere in the marine environment. Land coverage is based on a combination of 30 arc second Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM), Shuttle Radar Topography Mission3 (SRTM3 – 90m GDEM), EU-DEM (EU DEM based on ASTER and SRTM), and Global 1 (land DEM based on SRTM) second world-wide water body map for the topographic part. The compilation and void filling of the land DEM is based on the work of ViewFinderPanoramas.org . This global coverage layer will also be maintained in sync with the EMODnet DTM for Europe.
  The EMODnet Bathymetry World Base Layer provides an easy to use facility for all GIS users or WebGIS designers to get access to the current highest resolved topographic and bathymetric world-wide layout. One can get access to it by following this link: tiles.emodnet-bathymetry.eu .
  This site gives details about the WMTS Capabilities document and a Demo Viewer to try out a number of EMODnet DTM layers for Europe, the EBWBL for global coverage, and the various projections supported in the EBWBL WMTS service. The EBWBL layer has also been included in the layer menu of the Bathymetry Viewing and Download service.

  The EBWBL service is available in non-projected coordinate system (Lat, Long, WGS84: EPSG 4326), Web Mercator (EPSG 3857), Inspire compliant ETRS-EALA projection (EPSG 3035) and projections adapted to both poles (ESPG 3031 and 3996).

All these layers are made available in the Central Map Viewing service and for many layers additional functionalities are offered such as depth profiles along user drawn transects, 3D viewing of the bathymetry in the browser, retrieving metadata of surveys, and downloading of DTM tiles and other data products.

Moreover, most map layers are also made available as OGC web services. More details are given at the Central Portal Webservices.

Further upgrading of the EMODnet DTM is planned and will include incorporating even more surveys and further improvement of the digital bathymetry. For this purpose additional high resolution data sets are welcome and can be contributed using the EMODnet Ingestion service.

Geographic coverage

Bathymetric survey data sets are being catalogued as acquired and managed by European data providers for all regions in the world. The current 2020 release of the EMODnet Digital Terrain Model has a grid resolution of 1/16 * 1/16 arc minutes and covers the following European sea regions:

• the Greater North Sea,including the Kattegat and stretches of water such as Fair Isle, Cromarty, Forth, Forties,Dover, Wight, and Portland,
• the English Channel and Celtic Seas,
• Western Mediterranean, Ionian Sea and Central Mediterranean Sea,
• Iberi an Coast and Bay of Biscay (Atlantic Ocean),
• Adriatic Sea (Mediterranean),
• Aegean - Levantine Sea (Mediterranean),
• Madeira and Azores (Macaronesia),
• Baltic Sea,
• Black Sea,
• Norwegian and Icelandic Seas,
• Canary Islands (Macaronesia),
• European arctic region and Barentz Sea.

The geographic coverage of the EMODnet DTM for European sea regions is a Lat Lon box with 36W,15N; 43E,90N.

Vertical references

The bathymetric data as collected from the data providers, are supposed to be referenced at the Lowest Astronomical Tide (LAT) (International Hydrographic Office (IHO) resolution 3/1919) which is relevant for the vertical reference for nautical charts. Most Hydrographic Offices in Europe have adopted this IHO guideline. Therefore, the EMODnet Digital Terrian Model has been developed and is published for viewing and downloading in LAT.

Although IHO recommends LAT as the vertical reference for nautical charts, it is not an optimal vertical reference for several other applications such as hydrodynamical modelling near the coasts (tide, storm surge or waves). For this reason, efforts have been undertaken by EMODnet Bathymetry to enable converting the bathymetric model from LAT to MSL. Therefore, the following steps have been applied:

1. Modelling of LAT with respect to MSL with a numerical tide model for Europe;
2. Extending this, relatively coarse data, in very shallow and inter-tidal waters;
3. Adding the LAT-MSL difference to the LAT-referenced gridded bathymetry.

The numerical tide model ‘Global Tide Surge Model (GTSM)’ as developed and run by Deltares (NL) has been used as a robust model. This model is a worldwide model which is based on an unstructured mesh with the mesh decreasing to 25km in the middle of the oceans to 1.25km along the coasts of Europe. This model has been forced by the most recent and publicly recognised bathymetric and topographic information (EMODnet Bathymetry DTM in Europe and GEBCO 2019 for the rest of the world), along with tide generating forces including amongst other winds and surface pressure. Also the model has been extensively validated against tide measurements.

Using this method, the EMODNet DTM is also made available for downloading in MSL. This applies for the DTM tiles in the ESRI ASCII format, which are downloadable both in LAT and MSL.

QA/QC and DTM production details

Bathymetric survey data and aggregated bathymetry data sets have been collated from many data providers. These have been processed, quality controlled and used for the EMODnet DTM for European seas. The 2016 DTM version has a grid size of 1/8 * 1/8 arc minutes, while the 2018 and 2020 versions have an increased resolution of 1/16 * 1/16 arc minutes. Each grid cell has the following information:

• x, y coordinates;
• minimum water depth in metres to LAT;
• average water depth in metres to LAT;
• maximum water depth in metres to LAT;
• standard deviation of water depth in metres;
• number of values used for interpolation over the grid cell;
• interpolation flag (identification of extrapolated cells);
• average water depth smoothed by means of a spline function in metres to LAT;
• an indicator of the offsets between the average and smoothed water depth as a % of the water depth;
• reference to the prevailing source of data with metadata.

Note: The water depth values are in metres with reference to LAT.

The DTM values have been determined from 4 possible sources of data:

• Bathymetric survey data = high resolution data sets from single and multibeam surveys that are referenced via the CDI Data Discovery and Access service.
• Digital Terrain Model data = composite data sets produced and delivered by a number of external data providers such as Hydrographic Offices derived from their internal bathymetric database and based upon historic surveys. The aggregated data sets are referenced via the Sextant Catalogue service.
• Satellite Derived Bathymetry data = composite data sets produced from Landsat 8 and Sentinel images, in particular for coastal stretches in Greece, Spain, Croatia, Denmark, and Cyprus. The SDB data sets are referenced via the Sextant Catalogue service.
• GEBCO 2014 30” gridded data, used to complete area coverage in case there are no survey data or composite data sets available to the partners.

It is accepted that the accuracy and precision of the gridded data will vary over the basins in question. No new data has or will be collected specifically for this project. In case of multiple survey data for a cell, all surveys will be used for the calculations after having filtered datasets not satisfying to the QA/QC criteria.

GLOBE software : this software has been developed and is maintained by IFREMER . It has been customized for the EMODnet Bathymetry methodology and EMODnet Bathymetry partners make use of this software for processing their data contributions and for generating local and regional DTM's that are contributing to the EMODnet DTM. The EMODnet DTMs are provided in GLOBE NetCDF format and can be visualised by using the 3D visualisation tool of GLOBE software. More info about the GLOBE software can be found on the French Oceanographic Fleet website :

• Download the QA/QC manual;
• Download the manual for data providers about the DTM workflow;
• Download the manual for providing metadata input for Quality Index;
• Download the DTM format documentation.

Services

The EMODnet Bathyemtry portal provides a range of services and functionalities to users for viewing and downloading bathymetry data products and for identifying and requesting access to the survey data sets that are used as basis input for the DTM. Currently the following key services and functionality are provided for users:

1. Data Discovery and Access service provides functionality to search and obtain survey data sets;
2. Composite Products Discovery and Access service provides functionality to search and view metadata of composite DTM;
3. High-Resolution DTM Discovery and Access: provides functionality to search and obtain HR-DTMs.
4. Map Viewer service provides functionality to view, browse and download the DTM digital bathymetry and obtain information about the underlying data sets used to compile the DTM.

CDI Data Discovery and Access service

Data providers

In the field of bathymetry, a number of Data Centres in SeaDataNet manage bathymetric data sets, such as multibeam surveys from scientific cruises. There are other parties engaged in the provision of bathymetric data: Hydrographic Offices; Authorities; Research institutes; Industry.

These organisations perform and manage bathymetric surveys, partly overlapping and mostly complementing their geographical coverages. Data are collected at different frequencies and even date back to previous centuries. In addition, Satellite Derived Bathymetry data products are experiencing increased uptake because it is becoming an operational and robust technology. Optical sensor images provide a rapid and effective way to derive bathymetry in coastal zones up to 15 metres depth depending on the transparency of the water column.

Background

EMODnet Bathymetry was launched in 2009 with a steadily increasing number of services, metadata and data products. Currently, they are working on updated versions of the 2020 products.

Partnership

The EMODnet Bathymetry portal is operated and further developed by a European partnership. This comprises members of the SeaDataNet consortium together with organisations from marine science, the hydrographic survey community, and industry.
The partners combine expertises and experiences of collecting, processing, and managing of bathymetric data together with expertises in distributed data infrastructure development and operation and providing OGC services (WMS, WFS, and WCS) for viewing and distribution.

You can find the full and update list of the consortium on the following section of the website “Partners”.