Marine Themes DEM

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Dataset Description:

The Marine Themes Digital Elevation Model (DEM) product is a raster seabed surface model comprised of bathymetry data.  The DEM product has been compiled from a range of sources, depending upon availability:

  • Hydrographic survey data, where available – the most recent commercial single beam echo sounder (SBES) and multi-beam echo sounder (MBES) survey and LiDAR data (from a range of sources such as civil and military surveys, port and harbour authorities, pipeline and infrastructure surveys, and scientific and environmental studies)
  • Electronic Navigational Chart (ENC) or GEBCO data, where no survey data is available

These different sources have been combined via a de-confliction process (considering resolution, survey method, and acquisition date) and interpolated to provide a contiguous natural seabed surface which adjusts for issues such as differing chart datums and tidal corrections.  The DEM represents a Digital Surface Model (DSM) as it is compiled from the first reflection back to the sensor, and therefore features on the seabed such as shipwrecks and other manmade objects have not been removed and appear as ‘spikes’ in the surface.  New data sources will be incorporated into the DEM during the product revision cycle as they become available, with the coverage meta-layer updated as necessary.

The Marine Themes DEM product is available in two resolutions:

  • 1 arc second model (approx. 30m), supplied in 0.5 degree tiles, variable coverage
  • 6 arc second model (approx. 180m), supplied in 2 degree tiles, global coverage

The product has a global coverage and is supplied in WGS84 degree coordinates.  The horizontal datum of the DEM is the WGS84 Datum, and the vertical datum has been standardised on Chart Datum, which is commonly used by Hydrographic Offices and other organisations as the reference datum for marine depths as it approximates to Lowest Astronomical Tide (LAT).  As such this is not a geodetic datum and varies spatially according to tidal range.

In addition to the DEM data, the following ancillary files are also supplied to assist with the use of the product:

  • A spatial vector meta-layer which defines the original bathymetry data source via a range of attributes
  • A coastline feature to improve accuracies at coastal boundaries, attributed with heights extracted from the Vertical Offshore Reference Frame (VORF).  This is sourced from the High Water Line on the largest scale Electronic Navigational Chart (ENC) available for a given location, and corresponds spatially to the coastline feature (MTL Elevation) contained within OceanWise’s Marine Themes Vector product.  This defines a contiguous three dimensional break line
  • Symbology files (defining a recommended colour ramp for the DEM) and confidence grids are also available on request from OceanWise


Dataset Thumbnail:


Dataset Specification:

Product Name

Marine Themes DEM

Data Provider



Approx. 30m and 180m cell sizes


Global (30m incomplete, 180m complete)

Data Structure





Offshore seabed surface


OceanWise Licence

Update Frequency


Dataset Resources:

Product site
Marine and Coastal Data Products User Guide (pdf)
Metadata on MEDIN portal (xml)
Sample Data request site