http://www.bbc.co.uk/news/science-environment-11543990Two German radar satellites are now flying in tight formation as they prepare to make the most detailed ever 3D map of the Earth's entire surface.
TanDEM-X and TerraSAR-X have moved to within 350m of each other as they sweep around the planet at 7km/s.
The pair will soon begin an intense observation campaign that will pin down the variation in height across the globe to an accuracy of better than two metres.
Perhaps the best-known, near-global, space-borne DEM prior to the German venture came from the US Shuttle Radar Topography Mission (SRTM) of 2000. Its best product has a 30m by 30m spatial resolution, and a vertical resolution that varies from 16m to 10m.
With the TanDEM mission, the intention is to go down to a spatial resolution of 12m by 12m with a relative vertical accuracy of less than two metres.
Laser instruments (lidars) flown on planes can achieve better resolutions but their products are regional - they are not seamless maps of the whole Earth. TanDEM's will be.
Pretty impressive when you consider the speeds involved.
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