IN NATURAL sunlight, Earth looks stunning from space 鈥� no end of spectacular photographs bear this out. This isn鈥檛 one of them, however.
It鈥檚 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 the topography is precise down to a few millimetres. Not bad from an altitude of 800 kilometres.
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That鈥檚 why Envisat is attracting interest from far beyond the usual academic world. Insurance companies can use the satellite鈥檚 鈥渄igital elevation maps鈥� to see subsidence long before buildings begin to crumble. Vulcanologists can monitor whether volcanoes are deforming the ground 鈥� a sure sign that they are about to blow. Town planners can model the way water runs off the land to predict areas at risk of flooding. Envisat can track soil erosion, ice cover and the movement of glaciers with its microwave eyes.
It works by creating its own microwaves and beaming them towards Earth like an orbiting flashgun. It works as well at night as it does during the day, and it can also peer through cloud and haze. To increase the image resolution, the satellite takes several pictures of the same location as it moves through space and then combines them, a technique known as synthetic aperture radar. Since it is only measuring the intensity of reflection, the images are all black and white 鈥� this one is artificially coloured.
With Envisat鈥檚 new digital maps proving so useful, what does the future hold for conventional paper-based contour maps? Sadly, they will probably eventually join cathode ray tubes, video cassette recorders and film-based cameras as relics of a bygone era.