A digital elevation model is a digital model or 3D representation of a terrain’s surface created from terrain elevation data.
Commonly known and used are:
– Shuttle Radar Topography Mission (SRTM); see e.g. http://srtm.usgs.gov/ for details and have a look at the note below for 30m instead of 90m spatial resolution.
– ASTER Global Digital Elevation Mode (GDEM);
see e.g. http://asterweb.jpl.nasa.gov/gdem.asp for details.
– LiDAR – though this provides highest resolution it usually comes at the price of a big filesize and moreover currently LiDAR data tends to be not available for free. There may be some regional exceptions though. A positive example is the Chanel Coastal Observatory and its coastal LiDAR for parts of the UK.
“On September 23, 2014, the White House announced that the highest-resolution topographic data generated from NASA’s Shuttle Radar Topography Mission (SRTM) in 2000 will be released globally over the next year. The announcement was made at the United Nations Heads of State Climate Summit in New York.
Previously, SRTM data for regions outside the United States were sampled for public release at 3 arc-seconds, which is 1/1200th of a degree of latitude and longitude, or about 90 meters (295 feet). The new data are being released with a 1 arc-second, or about 30 meters (98 feet), sampling that reveals the full resolution of the original measurements. Data for most of Africa and its surrounding areas were released with the announcement. The next release is planned for later in 2014, and it is expected to include all of South America plus North America south of the United States.”
The new data are available for download from the USGS EROS Data Center.