EMODnet Bathymetry

A European seabed map, built since 2009

EMODnet, the European Marine Observation and Data network, was established in 2009 by the European Commission's Directorate-General for Maritime Affairs and Fisheries (DG MARE). Its aim is to gather marine data scattered across hundreds of institutes, harmonise it and make it free to use. Funded today by the European Maritime, Fisheries and Aquaculture Fund, it is organised in seven themes, bathymetry, geology, physics, chemistry, biology, seabed habitats and human activities, with over 130 partner organisations.

Its bathymetry service went online in 2010 with a first digital terrain model (DTM), a grid of depths covering the seabed without gaps, for selected European seas at 1/4 arc-minute. By the 2016 release the grid had been refined to 1/8 arc-minute and covered all European seas, and the release of September 2018 refined it again to 1/16 arc-minute, about 115 m.

Since then a new DTM has come out every two years: 2018, 2020, 2022 and 2024. The 2022 release, published in April 2023, was the first to include the Caribbean; the 2024 release, published in March 2025, is the current one. The consortium of hydrographic offices, research institutes and survey companies behind it is coordinated by Shom, the French navy's hydrographic and oceanographic service, while Ifremer maintains its processing software, GLOBE.

What it measures, and with what

The DTM gives, for each cell of a 1/16 by 1/16 arc-minute grid, about 115 by 115 m, the water depth, and with it the minimum, maximum and average of the depths in the cell, their standard deviation and the number of values used. A source reference layer names, cell by cell, the survey or compilation that prevails there, and a quality index adds indicators of its vertical and horizontal accuracy and of its age. Its area runs from 36W to 43E and from 15N to the pole, from the Azores and Canaries to the Baltic, the Black Sea and the Barents Sea, plus a Caribbean area from about 70W to 60W and 11N to 19N.

Most of the depths come from ships' echo sounders: single-beam ones, which measure one depth under the hull, and multibeam ones, which sweep a fan-shaped swath of seabed on each side of the track. Airborne lidar, a laser fired from an aircraft that reaches the bottom in clear shallow water, covers some coasts. Satellite-derived bathymetry, which estimates depth from the colour of the water in Landsat 8 and Sentinel-2 images, fills coastal strips of Greece, Spain, Croatia, Denmark, Cyprus and the Caribbean, down to about 15 m depending on water clarity.

The 2024 DTM draws on 21,890 survey datasets and 173 composite DTMs, compilations already gridded by a national office or a project. Some of these surveys are not open data: the consortium uses them with their owners' permission to build the grid but does not redistribute them. Where no survey exists, the gaps are filled from GEBCO and, in the Arctic, from IBCAO, the International Bathymetric Chart of the Arctic Ocean.

Depths refer to the Lowest Astronomical Tide (LAT), the lowest level the tide can be predicted to reach, which is the datum of most nautical charts. A version referred to mean sea level is also derived, using the Global Tide and Surge Model of the Dutch institute Deltares.

How a release is compiled

Each two-year cycle starts with gathering data: providers describe their new surveys in the SeaDataNet catalogue and their compiled models in the Sextant catalogue, then clean and grid them with GLOBE to EMODnet's standards. The seas are shared among regional groups, each led by a Regional Coordinator who assesses the contributions, selects the best data and compiles the regional DTM, replacing older surveys with newer and better ones and fixing anomalies found in the last release.

The regional models are then checked in a shared online workspace developed by Ifremer, which maps the differences between two releases, slopes, erratic peaks and isobaths, and lets the coordinators mark the anomalies still to fix. The regional pieces are merged into one grid, with GEBCO and IBCAO filling the gaps, and cut into 59 tiles that can be downloaded in netCDF and other formats.

The 2024 release added 20 new high-resolution areas, with large gains in the Atlantic thanks to Iceland's Marine and Freshwater Research Institute and the mapping of Portugal's continental shelf. Beyond the 115 m grid, more than 200 finer models, down to 1/512 arc-minute in coastal waters, are offered separately.

EMODnet's data products are owned by the European Union and licensed under Creative Commons CC BY 4.0: free to reuse, including commercially, provided EMODnet is credited. The metadata of the DTM states plainly that it is not to be used for navigation.

At sea: a fine grid, still not a chart

Where multibeam surveys exist, in the Channel, the North Sea or along much of the Atlantic shelf, cells of 115 m show banks, channels and shoals that a global grid smooths away. But a cell holds one value for more than a hectare of seabed: a rock, a wreck or a pinnacle much smaller than the cell can vanish in its mean, which is why the shallowest depth of each cell is published beside the mean. Where no survey exists and the grid is filled from GEBCO, it is no better than GEBCO.

Surveys also age. Sandbanks move on sandy, tide-swept bottoms such as the southern North Sea, and in some areas the prevailing survey is decades old; the quality index and the source reference layer tell how old and how good the data under a cell is.

Because depths refer to LAT, there is, as on a chart, more water than shown at nearly every state of the tide, but less in a strong offshore wind or a high-pressure system, and a cell with a depth close to zero holds almost no water at the lowest tides. EMODnet does not chart wrecks, buoyage or obstructions as a chart does, and the DTM is explicitly not for navigation: it helps to plan, the official charts are what to pilot by.

In Saily WR

Saily WR uses the EMODnet DTM 2024, at about 115 m (1/16 arc-minute), over Europe's seas, about 36W to 43E and 15N to 85N, and over the Caribbean, 70.5W to 59.5W and 11N to 19N. When you ask for a minimum depth, the depth is read from EMODnet wherever it covers, and from GEBCO elsewhere.

The same depths are drawn on the routing map as depth bands and isobaths, so you see the banks and channels a route goes round. Keep in mind the datum: inside EMODnet's area the depths are those of the lowest tide, while outside it GEBCO's refer to mean sea level, so the same minimum depth does not mean quite the same water on both sides of the edge.