The most complete terrain map of the Earth’s surface has been published.

The data, comprising 1.3 million images, come from a collaboration between the US space agency Nasa and the Japanese trade ministry.

The images were taken by Japan’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (Aster) aboard the Terra satellite.

The resulting Global Digital Elevation Map covers 99% of the Earth’s surface, and will be free to download and use.

The Terra satellite, dedicated to Earth monitoring missions, has shed light on issues ranging from algal blooms to volcano eruptions.

For the Aster measurements, local elevation was mapped with each point just 30m apart.

“This is the most complete, consistent global digital elevation data yet made available to the world,” said Woody Turner, Nasa programme scientist on the Aster mission.

“This unique global set of data will serve users and researchers from a wide array of disciplines that need elevation and terrain information.”

Previously, the most complete such topographic map was Nasa’s Shuttle Radar Topography Mission, covering 80% of the Earth’s surface. However, the mission’s results were less accurate in steep terrain and in some deserts.

Nasa is now working to combine those data with the new Aster observations to further improve on the global map. – BBC