GEBCO_2019 Grid

1.0 Introduction

The GEBCO_2019 Grid

The GEBCO_2019 Grid is the latest global bathymetric product released by the General Bathymetric Chart of the Oceans ( GEBCO ) and has been developed through the Nippon Foundation-GEBCO Seabed 2030 Project . This is a collaborative project between the Nippon Foundation of Japan and GEBCO. The Seabed 2030 Project aims to bring together all available bathymetric data to produce the definitive map of the world ocean floor and make it available to all.

The Nippon Foundation of Japan is a non-profit philanthropic organisation active around the world. GEBCO is an international group of mapping experts developing a range of bathymetric data sets and data products, operating under the joint auspices of the International Hydrographic Organization ( IHO ) and UNESCO 's Intergovernmental Oceanographic Commission ( IOC ).

The GEBCO_2019 product provides global coverage, spanning 89° 59' 52.5''N, 179° 59' 52.5''W to 89° 59' 52.5''S, 179° 59' 52.5''E on a 15 arc-second grid. It consists of 86400 rows x 43200 columns, giving 3,732,480,000 data points. The data values are pixel-centre registered i.e. they refer to elevations at the centre of grid cells.

The data are available to download according to the Terms of Use provided in Section 8 below, via several routes including: single-click download of the entire grid in NetCDF format, selection of subsets and creation of output in alternative data formats (see Section 5).

1.1 Seabed 2030 Data Center structure

This latest GEBCO product has been developed by the Seabed 2030 data centers, comprised of four Regional Centers and a Global Center.

The Regional Centers are responsible for championing mapping activities; assembling and compiling bathymetric information and collaborating with existing mapping initiatives in their regions. The Global Center is responsible for producing and delivering centralized GEBCO products, such as bathymetric grids.

Location of the Seabed 2030 Centers and their areas of responsibility.

Seabed 2030 Centers

• Southern Ocean - hosted at the Alfred Wegener Institute (AWI), Germany
• South and West Pacific Ocean - hosted at the National Institute of Water and Atmospheric Research (NIWA), New Zealand
• Atlantic and Indian Oceans - hosted at the Lamont Doherty Earth Observatory (LDEO), Columbia University, USA
• Arctic and North Pacific Oceans - hosted at Stockholm University (SU), Sweden and the Center for Coastal and Ocean Mapping at the University of New Hampshire (UNH), USA
• Global Data Center - hosted at the British Oceanographic Data Centre (BODC), National Oceanography Centre (NOC), UK

2.0 Grid Development

The GEBCO_2019 Grid is a continuous, global terrain model for ocean and land with a spatial resolution of 15 arc seconds.

The grid uses as a 'base' Version 1 of the SRTM15+ data set (Olson et al , 2014). This data set is a fusion of land topography with measured and estimated seafloor topography. It is largely based on version 11 of SRTM30+ (Becker et al , 2009; Sandwell et al , 2014), augmented with the gridded bathymetric data sets developed by the four Seabed 2030 Regional Centers. The published data were recalculated on a cell-registered grid for use by GEBCO.

The Regional Centers have compiled gridded bathymetric data sets, largely based on multibeam data, on a sub-set of the global grid for their areas of responsibility. These regional grids were then provided these to the Global Center. For areas outside of the polar regions (primarily south of 60N and north of 50S), these data sets are in the form of 'sparse grids', i.e. only grid cells that contain data were populated. For the polar regions, complete grids were provided due to the complexities of incorporating data held in polar coordinates.

The compilation of the GEBCO_2019 Grid from these regional data grids, with some additional source data sets, was carried out at the Global Center, with the aim of producing a seamless global terrain model.

The majority of the work, for the non-polar regions, was done using the 'remove-restore' procedure (Smith and Sandwell, 1997; Becker, Sandwell and Smith, 2009 and Hell and Jakobsson, 2011). This is a two stage process of computing the difference between the new data and the 'base' grid, gridding the difference and adding this difference back to the existing 'base' grid. The aim is to achieve a smooth transition between the 'new' and 'base' data sets with the minimum of perturbation of the existing base data set.

For the polar data sets, and the adjoining North Sea area, supplied in the form of complete grids these data sets were included using feather blending techniques from GlobalMapper software version 11.01, made available by Blue Marble Geographic .

The GEBCO_2019 Grid includes data sets from a number of international and national data repositories and regional mapping initiatives. For information on the data sets included in the GEBCO_2019 Grid, please see Section 11 below.

3.0 Land Data

The land data in the GEBCO Grid are taken directly from SRTM15+ for all areas outside the Polar regions.

South of 60°S, the land topography is determined from Bedmap2 (Fretwell et al , 2013).

4.0 GEBCO Source Identifier (SID) Grid

The GEBCO Grid is accompanied by a Source Identifier (SID) grid. This data set identifies which of the corresponding grid cells in the GEBCO Grid are based on bathymetric soundings or bathymetric depth values from grids and which cells contain predicted or interpolated depth values. Further information about the format and coding of the data set is given below.

4.1 GEBCO SID Grid coding

The table below details the coding of the GEBCO_2019 Source Identifier (SID) grid.

5.0 Data Dissemination

GEBCO's gridded data sets are made available as a global file in CF-netCDF format and for user-defined areas in CF-netCDF, Esri ASCII raster or data GeoTiff.

The complete data set provides global coverage, spanning 89° 59' 52.5''N, 179° 59' 52.5''W to 89° 59' 52.5''S, 179° 59' 52.5''E on a 15 arc-second grid. It consists of 86400 rows x 43200 columns, giving 3,732,480,000 data points. The data values are pixel-centre registered i.e. they refer to elevations at the centre of grid cells.

The gridded data are available to download in a number of different formats as described in the following sections.

5.1 CF-netCDF format

A single, global CF-netCDF format file file is available for single-click download.

Within the file, the GEBCO_2019 Grid is stored as a two-dimensional array of 32-bit float values of elevation in metres, with negative values for bathymetric depths and positive values for topographic heights. The netCDF storage is arranged as contiguous latitudinal bands. The total dataset is 12Gb.

The data file includes header information which conforms to the NetCDF Climate and Forecast (CF) Metadata Convention v1.6 ( http://cfconventions.org/ ).

The GEBCO_2019 SID grid is provided in the same array format, but data are stored as a two-dimensional array of 2-byte integers.

5.2 Esri ASCII raster format

This is an ASCII format developed for the export/exchange of Esri ARC/INFO rasters. The format consists of a header that gives the geographic extent and grid interval of the data set, followed by the actual grid cell data values. The GEBCO_2019 Grid and SID grids are made available as single-channel float and integer data values respectively, for user-defined areas, in Esri ASCII raster format using the download tool .

5.3 Data GeoTIFF

The GeoTiff format contains geo-referencing (geographic extent and projection) information embedded within a Tiff file. The GEBCO_2019 Grid and SID grids are made available as single-channel float and integer data values respectively for user-defined areas in GeoTiff format using the download tool .

6.0 GEBCO's grids and vertical datum

GEBCO's global elevation models are generated by the assimilation of heterogeneous data types, assuming all of them to be referred to mean sea level. However, in some shallow water areas, the grids include data from sources having a vertical datum other than mean sea level. We are working to understand how best to fully assimilate these data.

7.0 Data set attribution

If the data sets are used in a presentation or publication then we ask that you acknowledge the source. This should be of the form:

GEBCO Compilation Group (2019) GEBCO 2019 Grid (doi:10.5285/836f016a-33be-6ddc-e053-6c86abc0788e)

8.0 Terms of use and disclaimer

Scope

• These terms of use apply to The GEBCO Grid and other GEBCO-derived information products
• For brevity 'The GEBCO Grid' is used throughout and should be interpreted as meaning The GEBCO Grid and other GEBCO-derived information products
• Bathymetric Data refers to measurements made by various instruments of the ocean depth, associated ocean properties and the supporting metadata
• Information products are the result of applying algorithms, mathematical techniques, scientific theory and Intellectual Property to data to create useful, derived values
• As the GEBCO Grid is created by interpolating, applying algorithms and mathematical techniques to bathymetric data, GEBCO considers the GEBCO Grid to be an information product
• GEBCO does not provide the underlying source bathymetric data when distributing the GEBCO Grid

Terms of use

The GEBCO Grid is placed in the public domain and may be used free of charge.

Use of the GEBCO Grid indicates that the user accepts the conditions of use and disclaimer information given below.

Users are free to:

• Copy, publish, distribute and transmit The GEBCO Grid
• Adapt The GEBCO Grid
• Commercially exploit The GEBCO Grid, by, for example, combining it with other information, or by including it in their own product or application

Users must:

• Acknowledge the source of The GEBCO Grid. A suitable form of attribution is given in the documentation that accompanies The GEBCO Grid.
• Not use The GEBCO Grid in a way that suggests any official status or that GEBCO, or the IHO or IOC, endorses any particular application of The GEBCO Grid.
• Not mislead others or misrepresent The GEBCO Grid or its source.

Disclaimer

• The GEBCO Grid should NOT be used for navigation or for any other purpose involving safety at sea.
• The GEBCO Grid is made available 'as is'. While every effort has been made to ensure reliability within the limits of present knowledge, the accuracy and completeness of The GEBCO Grid cannot be guaranteed. No responsibility can be accepted by GEBCO, IHO, IOC, or those involved in its creation or publication for any consequential loss, injury or damage arising from its use or for determining the fitness of The GEBCO Grid for any particular use.
• The GEBCO Grid is based on bathymetric data from many different sources of varying quality and coverage.
• As The GEBCO Grid is an information product created by interpolation of measured data, the resolution of The GEBCO Grid may be significantly different to that of the resolution of the underlying measured data.

9.0 Reporting bugs in the GEBCO Grid

While every effort is made to produce an error free grid, some artefacts may still appear in the data set. Please see our errata web page for information on known bugs in the dataset.

If you find any anomalies in the grid then please report them via email ( gdacc@seabed2030.org ), giving the problem location, and we will investigate.

10.0 References

Olson, C J, Becker, J J and Sandwell, D T (2014). A new global bathymetry map at 15 arcsecond resolution for resolving seafloor fabric: SRTM15_PLUS, AGU Fall Meeting Abstracts 2014.

Becker, J J, D T Sandwell, W H F Smith, J Braud, B Binder, J Depner, D Fabre, J. Factor, S Ingalls, S-H Kim, R Ladner, K Marks, S Nelson, A Pharaoh, R Trimmer, J Von Rosenberg, G Wallace, P Weatherall (2009). Global Bathymetry and Elevation Data at 30 Arc Seconds Resolution: SRTM30_PLUS, Marine Geodesy, 32:4, 355-371.

Sandwell, D T., R D Müller, W H F Smith, E Garcia, R Francis (2014). New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure, Science, Vol. 346, no. 6205, pp. 65-67, doi: 10.1126/science.1258213 .

Smith, W H F and D T Sandwell (1997). Global seafloor topography from satellite altimetry and ship depth soundings, Science, v. 277, p. 1957-1962, 26 Sept.

Hell, B and M Jakobsson (2011), Gridding heterogeneous bathymetric data sets with stacked continuous curvature splines in tension, Mar. Geophys. Res., 32(4), 493-501, doi:10.1007/s11001-011-9141-1 .

Fretwell, P, H D Pritchard D G Vaughan, J L Bamber, N E Barrand, R Bell, C. Bianchi, R G Bingham, D D Blankenship, G Casassa, G Catania, D Callens, H Conway, A J Cook, H F J Corr, D Damaske,V Damm, F Ferraccioli, R Forsberg, S Fujita, Y Gim, P Gogineni, J A Griggs, R C A Hindmarsh, P Holmlund, J W Holt, R W Jacobel, A Jenkins, W Jokat, T Jordan, E C King, J Kohler, W Krabill, M Riger-Kusk, K A Langley, G Leitchenkov, C Leusche, B P Luyendyk, K Matsuoka, J Mouginot,F O Nitsche, Y Nogi, O A Nost, S V Popov, E Rignot, D M Rippin, A Rivera, J Roberts, N Ros,M J Sieger, A M Smith, D Steinhage, M Studinger, B Sun, B K Tinto, B C Welch, D Wilson, D A Young, C Xiangbin and A Zirizzotti (2013). Bedmap2: improved ice bed, surface and thickness datasets for Antarctica, The Cryosphere, 7, 375-393, 2013. doi.org/10.5194/tc-7-375-2013

11.0 Data sets included in the GEBCO_2019 Grid

Compilations and gridded contributions

Multibeam Survey data

Other contributions