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IN NATURAL sunlight, Earth looks stunning from space – no end of spectacular photographs bear this out. This isn’t one of them, however.

It’s a microwave radar image of the Congo river in central Africa taken by Envisat, the largest Earth observation satellite ever built. Envisat was launched by the European Space Agency in 2002, and its unique vision is changing the way we look at the planet.

It only has a modest resolution, but Envisat has a useful trick up its sleeve: it can measure distances incredibly precisely. Images like this one can be turned into 3D maps in which…