Soldiers have been moving troops and equipment under cover of clouds and darkness for decades. In the past few years, though, an alternative to visibile light has been making big strides
The success was not in itself trendsetting. When France, Britain and Prussia met 21 years later at Waterloo, 30km north of Fleurus, no one looked down but the birds: Napoleon had abolished the Aerostatic Corps in 1799. Military ballooning did not really come into its own until the American civil war, and its importance was short lived.
In the past few years, though, an alternative to visible wavelengths has been making enormous strides. The satellites from which Ursa draws its images are built around radio antennae, not lenses. These orbiting radars illuminate the surface using wavelengths hundreds of thousands of times longer than those of visible light. Such wavelengths pass easily through clouds, fog, smog and, when necessary, camouflage netting before hitting the surface and bouncing back out into space.
This technology has been available since the 1960s, and used by spy satellites since the 1980s. But it was limited, expensive and highly classified. It was not until the late 2000s, when India and Israel both had militarysatellites of their own that America’s National Reconnaissance Office, an arm of the Pentagon, declassified the existence of its own such satellites, finally allowing its employees to talk to Air Force officers about them.
And changes at a specific site can be analysed with remarkable precision. Radar systems can get data from the phase of the waves they are using in ways that optical systems using ambient light cannot. The “coherent change detection” this allows can show up even minute anomalies.
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