2-Minute Gridded Global Relief Data (ETOPO2v2)
|Online: images, data (access latest relief model)|
The 2006 ETOPO2v2 data structure, provenance changes and updates
(Differences from the 2001 version of ETOPO2) are:
ETOPO2v2 eliminates a 1-cell westward bias that was present in ETOPO2 (2001).
ETOPO2v2 is available in both a
downloadable cell-centered version, named ETOPO2v2c (pixel registered, where the cell boundaries are lines of even minutes of latitude and longitude, centered on intersections of lines of odd minutes of latitude and longitude) and a
grid-centered, version, available via design-a-grid (with cell boundaries defined by lines of odd minutes of latitude and longitude, meaning that cells were centered on the integer multiples of 2 minutes [even minutes] of latitude and longitude). The cell-centered grid is the authoritative version. The grid-centered version was derived from the cell-centered grid and the conversion produces slightly flattened relief. This is a change from the original ETOPO2 (2001), which was available as grid-registered only.
Coverage of ETOPO2v2 is -90° to +90° in Latitude, and -180° to +180° in Longitude, whereas ETOPO2 (2001) covered +90° to -89°58' in Latitude and -180W° to +179°58' in Longitude.
The ETOPO2v2c, with cell centered-registration, eliminates the ETOPO2 North Pole redundancies but has the same number of cells: 5,400 rows of data (180 x 30), each with 10,800 columns of data (360x30). The first row of 10,800 (360 x 30) cells in ETOPO2 (2001) redundantly repeated the same data value, centered on the north pole. A data row, centered on the South Pole, was not included in the original ETOPO2 (2001).
Land topography was resampled from the
GLOBE Project (1999) to ensure proper registration with the 2' ETOPO2v2 grid.
Bathymetric data for the Caspian Sea were obtained as digitized contours from the Caspian Environment
For coastal US waters, the NCEI Coastal Relief Model (CRM) 3" grids from CRM Volumes 1-10 were sampled to 2' cell averages for bathymetry.
Great Lakes bathymetric data were sampled to 2' cell averages from 3" NCEI source grids for Lakes Erie, Ontario, Huron, and Michigan; preliminary 30" source data were used for Lake Superior.
Smith & Sandwell
The "Smith & Sandwell" database is a worldwide set of 2-minute gridded ocean bathymetry derived from 1978 satellite radar altimetry of the sea surface. The version contained in ETOPO2v2 is 8.2.
The "Global Land One-kilometer Base Elevation" (GLOBE) database is made up of data sets from more than eight US and foreign agencies. It covers all of the world's land masses at a resolution of 0.5 minute (30") of latitude and longitude, which is approximately one kilometer at the equator. GLOBE data were sampled to 2' cell averages for all land areas.
The International Bathymetric Chart of the Arctic Ocean (IBCAO) initiative developed a digital database that contains all available bathymetric data north of 64 degrees North. The version contained in ETOPO2v2 is 1.0, sampled to 2' cell averages.
NCEI Coastal Relief Model (CRM)
The Coastal Relief Model (CRM) is used for US waters from the coastline to as far offshore as the NOS hydrographic data will support a continuous view of the seafloor. Data were sampled to 2' cell averages for areas adjacent to all 48 conterminous states, Hawaii, and Puerto Rico.
Great Lakes Bathymetric Data
Great Lakes bathymetric data were sampled to 2' cell averages for all five Great Lakes. 3" source grids were available for lakes Huron, Michigan, Erie, and Ontario; preliminary 30" grid data were sampled for Lake Superior. All lake depth data were made consistent with surrounding land elevations and each lake's mean level datum.
Caspian Sea Bathymetry
Bathymetry data for the Caspian Sea were obtained as digitized depth contours from the Caspian Environment Programme website. The digitized contours were analyzed with surface-fitting software to produce a digital bathymetric grid registered to the same coordinate system as the rest of ETOPO2v2, and made consistent with the surrounding land elevations -- the surface of the Caspian Sea is approximately 29m below Mean Sea Level.
- What are the datums (horizontal and vertical references) for ETOPO2v2?
The horizontal datum is WGS-84, the vertical datum is Mean Sea Level.
- How does one cite ETOPO2v2?
See: doi: 10.7289/V5J1012Q
(more about how to cite data and images)
- What is the resolution of ETOPO2v2?
The horizontal grid spacing is 2-minutes of latitude and longitude (1 minute of latitude = 1.853 km at the Equator). The vertical precision is 1 meter.
- What is the projection of ETOPO2v2?
ETOPO2v2 is in the Cylindrical Equidistant Projection (sometimes called Latitude-Longitude, or Geographic).
- What do the grid data actually represent?
The grid values represent the elevation at the grid intersections at odd multiples of 2 minutes of latitude and longitude, averaged over the cell's area.
- Is the sea floor really that bumpy, and what are the long, straight lines on the ocean floor that converge on places like San Diego and Bermuda?
The "orange-peel" look of the sea floor may be an artifact of the satellite altimetry technology and its interpretation of ocean surface waves. The straight lines are where direct shipborne measurements have been included in the data as "ground truth". These measurements help calibrate, but do not correspond 100 percent to the radar altimetry. See W.H.F. Smith and D.T. Sandwell, 1997, Global Sea Floor Topography from Satellite Altimetry and Ship Depth Soundings, Science 277 (5334), p.1956-1962.
- What about shallow (<200m) water?
The satellite altimetry works best in deep water and can distinguish many undersea features that are not otherwise surveyed directly. In shallow water, the gravitational effects that can be measured from the satellite are too small to be reliable. In US waters and some other areas, local high-resolution survey data have been used where available.
- How do I run ETOPO2v2?
ETOPO2v2 is a database, not a program. You will need imaging or analysis software to use the data.