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Bathymetry and Topography

Contents

Background

  • Bathymetry (depth values of the sea floor) and topography (height values of the land surface; also called hypsometry), taken together, are called global relief. These data have been essential, from ancient times, for the works of man. Every Roman aquaduct was carefully surveyed to make certain that it ran properly downhill at a precise declination. And all clement seaways, since mankind took to sea in boats, have been determined first and foremost on the basis of sufficient depth (at high AND low tides) for passage. During the past century, knowledge of relief has grown even more important, at finer scales and higher resolution than ever dreamed of previously. Although general marine work may not require the very highest resolution data, data managers should be aware of the major resources available, and how to use them. This brief introduction is intended to provide just the barest outline, which can lead to further study, if necessary.
  • See also the related article on Coastlines and Land Masks.

Grids versus Charts

Relief data can be in the form of rectilinear grids (essentially analyses of thousands or millions of data points) or in the form of charts (essentially line drawings [vectors] of coasts, physical features, and depth contours). Grids are used for scientific purposes, and as an aid in drawing charts, but they are not for navigation. Charts for navigation are drawn up from many sources, only one of which is gridded data. This article has nothing to do with navigation and no recommendation in it should be applied to navigation.

Rectilinear vs. Conforming Grids

All of the major databases below are regular (i.e. rectilinear) grids. Modelers frequently use exotic grids that conform to the coastline or to the bathymetry or both (i.e. curvilinear). In this way the grid cells can be much smaller in shallow areas or narrow passages, in order to resolve important features. In such cases, the databases listed here would only be used as the starting point for creating the conforming grid.

Major Grid Databases

DBDB5

"The "Digital Bathymetric Data Base 5 minute" (DBDB5) was assembled by the US Naval Oceanographic Office in the early 1980's from computer interpolation of existing contour maps of ocean basins." [From the GCMD record cited below] It is apparently complete superseded by other resources, and no longer in use.

ETOPO5

"ETOPO5 was generated from a digital data base of land and sea-floor elevations on a 5-minute latitude/longitude grid. The resolution of the gridded data varies from true 5-minute for the ocean floors, the USA., Europe, Japan,and Australia to 1 degree in data-deficient parts of Asia, South America, northern Canada, and Africa." [From the NGDC ETOPO5 page cited below]. Although it has been superseded by two generations of better relief models, it is still in wide use, especially by modelers.

ETOPO2

Two-minute gridded global relief for both ocean and land areas. The original ETOPO 2 Version 1 (2001) was replaced by Version 2 (2006). Version 2 is available in both vertex-centered and cell-centered versions. [Vertex centering is called "grid centering" at NGDC.]

ETOPO1

"ETOPO1 is a 1 arc-minute global relief model of Earth's surface that integrates land topography and ocean bathymetry. It was built from numerous global and regional data sets, and is available in "Ice Surface" (top of Antarctic and Greenland ice sheets) and "Bedrock" (base of the ice sheets) versions." [From the NGDC page cited below.] Also available in cell- and vertex-centered versions. Unless a better source for local or regional data is known to exist (and has been tested), this source should be used for large-scale work.

GEBCO

The General Bathymetric Chart of the Oceans is, literally, a master set of mylar charts of the seas, hand contoured by experts. Paper copies are widely published and available. A digital version is also available, and it is frequently used in OceanTeacher training (see the Exercise below). The XYZ coordinates of the hand-drawn contour lines have been gridded to create the so-called GEBCO gridded bathymetry; this practice and result are not without controversy.

GTOPO30

Global 1-km digital raster data (land only) derived from a variety of sources, published by the EROS Data Center.

SRTM

The Shuttle Radar Topography Mission has yielded a variety of high-resolution land-only, relief products. The global dataset (60 N to 56 S) is available at 3 arc seconds, in various formats. The files can be extremely large, so use caution if you really want to work at this high resolution.

Major Chart and Contour Databases

  • GEBCO - See below
  • Additional items pending

Additional Resources


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Information about this article

Short title: Bathymetry and Topography

Description: none

Expertise level: beginner

Author: Murray.Brown

Approval status: approved

Approved by: Murray.Brown

Last change: 2010-1-12

Subsection of: Geospatial Data Concepts

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