Land/Ice Elevations and Seafloor Depths

Basemap Description (GMRT)

The Global Multi-Resolution Topography imagery for the Basemap has been generated at the Lamont-Doherty Earth Observatory of Columbia University with funding from the US National Science Foundation. For the land regions, we used the gridded digital elevation datasets provided by the Shuttle Radar Topography Mission, the ASTER Global Digital Elevation Model, and the National Elevation Dataset of the United States. For the seabed we incorporated version 6.0 of the SRTM30_PLUS from the Sandwell Lab, the Arctic bathymetry from version 2.0 of International Bathymetric Chart of the Oceans and combined these datasets with individual digital swath echo-soundings from more than 400 major oceanographic expeditions and more than 100 coastal surveys of the National Oceanographic and Atmospheric Agency. The elevations and depths are complied into a nested set of tiles spanning 11 doublings in magnification to an ultimate spatial resolution of 10 meters per pixel on land (US) and 4 meters per pixel in offshore coastal regions. For the Arctic and Antarctic ploar projections we used the sub-ice land elevations from NSIDC for Greenland and the BEDMAP for Antartica.

Web Link: http://www.geomapapp.org/
Citation: Ryan, W. B. F., et al. (2009), Global Multi-Resolution Topography synthesis, Geochem. Geophys. Geosyst., 10, Q03014, doi:10.1029/2008GC002332.

Data Sources

Shuttle Radar Topography Mission (SRTM)
The Shuttle Radar Topography Mission (SRTM) obtained elevation data on a near-global scale to generate tan almost complete high-resolution digital topographic database of Earth. SRTM consisted of a specially modified radar system that flew onboard the Space Shuttle Endeavour during an 11-day mission in February of 2000. SRTM is an international project spearheaded by the National Geospatial-Intelligence Agency (NGA) and the National Aeronautics and Space Administration (NASA). The SRTM spatial resolution is 3 arc-sec (~90 meters) globally and 1 arc-sec (~30 meters) for the United States mainland and Hawaii.

Web Link: http://www2.jpl.nasa.gov/srtm/
Citation: Farr, T. G., et al. (2007), The Shuttle Radar Topography Mission, Rev. Geophys., 45, RG2004, doi:10.1029/2005RG000183.

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)
ASTER is an imaging instrument flying on Terra, a satellite launched in December 1999 as part of NASA's Earth Observing System (EOS). ASTER is a cooperative effort between NASA, Japan's Ministry of Economy, Trade and Industry (METI) and Japan's Earth Remote Sensing Data Analysis Center (ERSDAC). ASTER is being used to obtain detailed maps of land surface temperature, reflectance and elevation. The three EOS platforms are part of NASA's Science Mission Directorate whose goal is to observe, understand, and model the Earth system to discover how it is changing, to better predict change, and to understand the consequences for life on Earth. The current ASTER Digital Elevation Model (DEM) product was implemented using new production software at the Land Processes DAAC starting on May 24, 2006. This is the final validated version of the DEM product derived using bands 3N and 3B from an ASTER Level-1A data set. All current ASTER DEM products are generated without using ground control points (GCPs).

Web Link: http://asterweb.jpl.nasa.gov/

SRTM30_PLUS
The 30-arc second (~900 meter) resolution global topography/bathymetry grid (SRTM30_PLUS) has been developed at the Scripps Institution of Oceanography under the direction of David T. Sandwell from a wide variety of data sources. Land and ice topography comes from the SRTM30 and ICESat topography, respectively. Ocean bathymetry is based on a new satellite-gravity model where the gravity-to-topography ratio is calibrated using 298 million edited soundings. The main contribution of this study is the compilation and editing of the raw soundings, which come from NOAA, individual scientists, SIO, NGA, JAMSTEC, IFREMER, GEBCO, and NAVOCEANO.

Web Link: http://topex.ucsd.edu/WWW_html/srtm30_plus.html
Citation: 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., Global Bathymetry and Elevation Data at 30 Arc Seconds Resolution: SRTM30_PLUS, Marine Geodesy, 32:4, 355-371, 2009. DOI: 10.1080/01490410903297766

International Bathymetric Chart of the Artic Ocean (IBCAO)
The goal of this initiative is to develop a digital database that contains all available bathymetric data north of 64 degrees North, for use by mapmakers, researchers, and others whose work requires a detailed and accurate knowledge of the depth and the shape of the Arctic seabed. Version 2.0 of the IBCAO Grid includes the recent years of multibeam mapping. The resolution of the Polarstereographic grid has been increased to 2-km.

Web Link: http://www.ngdc.noaa.gov/mgg/bathymetry/arctic/arctic.html
Citation: Jakobsson, M., Macnab, R., Mayer, L., Anderson, R., Edwards, M., Hatzky, J., Schenke, H-W., and Johnson, P., 2008, An improved bathymetric portrayal of the Arctic Ocean: Implications for ocean modeling and geological, geophysical and oceanographic analyses, v. 35, L07602, Geophysical Research Letters, doi:10.1029/2008GL033520

General Bathymetric Chart of the Oceans (GEBCO)
The General Bathymetric Chart of the Oceans (GEBCO) consists of an international group of experts who work on the development of a range of bathymetric data sets and data products, including gridded bathymetric data sets, the GEBCO Digital Atlas, the GEBCO world map and the GEBCO Gazetteer of Undersea Feature Names. Through the work of its committees and working groups, GEBCO produces and makes available a range of bathymetric data sets and products. The GEBCO_08 Grid at a 30 arc-second (~900 meter) was updated November 2009. The grid has been generated by combining quality-controlled ship depth soundings with interpolation between sounding points guided by satellite-derived gravity data. The GEBCO_08 Grid is currently a development product, which will undergo periodic update. Although every effort has been made to reduce the number of errors in the data set, we expect that some grid artifacts will be found.

Web Link: http://www.gebco.net/

Subglacial Topographic Model of the Antarctic (BEDMAP)
Data describing the thickness of the Antarctic ice sheet (collected on surveys undertaken over the past 50 years) have been brought together into a single database. These data have allowed the compilation of a suite of seamless digital topographic models for the Antarctic continent and surrounding ocean. The suite includes grids representing; ice-sheet thickness over the ice sheet and shelves water-column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet bathymetry to 60 South including the areas beneath the ice shelves. These grids are consistent with a recent high-resolution surface elevation model of Antarctica. While the digital models have a nominal spatial resolution of 5 km, such high resolution is not strictly justified by the original data density over all parts of the ice sheet. The suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modelling. The bed elevation digital elevation model, which includes the entire geosphere south of 60 South, provides an improved delineation of the boundary of the boundary between East and West Antarctica and sheds new light on the morphology of the contiguous East Antarctic landmass, much of which is buried below an average of 2500 m of ice.

Web Link: http://www.antarctica.ac.uk//bas_research/data/access/bedmap/
Citation: Lythe, M.B., Vaughan, D.G. and the BEDMAP Consortium. 2000. BEDMAP - bed topography of the Antarctic. 1:10,000,000 scale map. BAS (Misc) 9. Cambridge, British Antarctic Survey.

The ICESAt Geoscience Laser Altimeter System (GLAS)
The National Snow and Ice Data Center (NSDIDC) archives and distributes data products from the Geoscience Laser Altimeter System (GLAS) instrument aboard the NASA Ice, Cloud, and land Elevation (ICESat) satellite, launched on 12 January 2003. The main objective of the GLAS instrument is to measure ice sheet elevations and changes in elevation through time. Secondary objectives include measurement of cloud and aerosol height profiles, land elevation and vegetation cover, and sea ice thickness.

Web Link: http://nsidc.org/data/icesat/index.html
Citations: Bamber, J. L., J. L. Gomez-Dans, and J. A. Griggs. 2009. A New 1 km Digital Elevation Model of the Antarctic Derived from Combined Satellite Radar and Laser Data - Part 1: Data and Methods. The Cryosphere 3: 101-111.
Griggs, J. A. and J. L. Bamber. 2009. A New 1 km Digital Elevation Model of Antarctica Derived from Combined Radar and Laser Data - Part 2: Validation and Error Estimates. The Cryosphere 3: 113-123.
DiMarzio, J., A. Brenner, R. Schutz, C. A. Shuman, and H. J. Zwally. 2007. GLAS/ICESat 500 m laser altimetry digital elevation model of Antarctica. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.
DiMarzio, J., A. Brenner, R. Schutz, C. A. Shuman, and H. J. Zwally. 2007. GLAS/ICESat 1 km laser altimetry digital elevation model of Greenland. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.