ACE2 is now available for free download at:




The ACE2 project is a contract with ESA ESRIN to produce the most comprehensive and accurate Global Digital Elevation Model of the Earth to date.

The Shuttle Radar Topographic Mission has generated a unique and valuable dataset, allowing the generation of a Digital Elevation Model of unprecedented accuracy and spatial resolution over much of the earthÕs land surface. However the SRTM has some problems with areas such as Rainforests and inland water due to the nature of the instrument used. The ACE2 Global Digital Elevation model will be a fusion of the SRTM dataset with Altimeter datasets from the ERS-1 Geodetic Mission, ERS-2, EnviSat and Jason missions where good data are derived. The SRTM covered latitudes between 60° North and 54° South with a resolution of 3 arc seconds. The ACE2 GDEM will keep the 3 arc second resolution, however all of the Earth's land surface will be included.

Over much of the Earth's surface the two datasets show very good agreement within the SRTM's stated accuracy of ±16m, in these areas the SRTM values will be warped to the Altimeter values and the precision will be increased from metres to decimetres. Over areas where the SRTM height values were biased due to the foliage the Altimeter values will be used to warp the SRTM values so the tree heights are removed and the height of the ground remains.

A comparison of the SRTM dataset with ERS-1 Geodetic Mission heights

Comparison of the SRTM dataset with ERS-1 Geodetic Mission heights for areas within the SRTM stated accuracy of ±16m