IMINT

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IMINT, short for IMagery INTelligence, is an intelligence gathering discipline which collects information via satellite and aerial photography.

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Satellites

There have been dozens - of reconnaissance satellites launched by dozens of nations since Sputnik. While the vast majority of such satellites and any information concerning them are strictly classified, some information (such as that concerning the US Corona program) has been declassified with the end of the Cold War.

The exact resolution and other details of spy satellites are classified, but some idea of the trade-offs available can be made using simple physics. The formula for the resolution of an optical system is given by the Rayleigh criterion:

<math> \sin \theta = 1.22 \frac{\lambda}{D}</math>

where θ is the angular resolution, λ is the wavelength of light, and D is the diameter of the lens or mirror.

A spy satellite would probably be placed in a low-earth orbit and we might take an altitude of 300 km as a reasonable guess. Such a satellite might have comparable optical performance to the Hubble telescope, which has a 2.4 metre mirror telescope. If it were to be used to take photographs using visible light then the wavelength will be in the range 400 to 700 nanometres. We might take 550 nm as a suitable guess. From the Rayleigh formula the resulting angular resolution would be 229 nrad, which at a height of 300 km corresponds to an object about 7 cm across. This is a best-case estimate and does not include the blurring effects of the atmosphere. Of course there is no reason why the orbit needs to be circular. Elliptical orbits would provide closer passes over certain regions of interest.

The primary purpose of most spy satellites is to monitor visible ground activity. While resolution and clarity of images has improved greatly over the years, this role has remained essentially the same. Some other uses of satellite imaging have been to produce detailed 3D maps for use in operations and missile guidance systems, and to monitor normally invisible information such as the growth levels of a country's crops or the heat given off by certain facilities.

To counter the threat posed by these 'eyes in the sky', several nations (the United States and the USSR/Russia at least) have developed systems for destroying enemy spy satellites (either with the use of another 'killer satellite', or with some sort of earth or air launched missile).

The spy satellite game has taken a strange new twist with the recent availability of high resolution, colour images from commercial satellite imaging companies - allowing any country (or any individual for that matter) to get in on the action.

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Aerial

Aerial intelligence goes back hundreds of years. Long in the past (the American Civil War for example) hot air balloons were used to observe enemy formations long in the distance. The use of fixed balloons survived into World War I, when it was accompanied by observation from airships (zeppelins) and the newly invented airplane. In WW2 a Joint Imagery Intelligence unit was set up in Danesfield House, Medmenham in Buckinghamshire, UK for British and US Intelligence Officers to exploite imagery gathered on the Germans.

Low- and high-flying planes have been used all through the last century to gather intelligence about the enemy. At the start of the Cold War, foreseeing the need to observe the enemy in peacetime as well as war, the U.S. developed high-flying reconnaissance planes. The first, the Lockheed U-2, is still in service; its successor, the newer, much faster SR-71 Blackbird, was retired in 1998. These planes have the advantage over satellites that they can usually produce more detailed photographs and can be placed over the target more quickly, more often, and more cheaply, but have the obvious disadvantage that they can be shot down. (However, there is no evidence an SR-71 was ever shot down.)

A new generation of unmanned reconnaissance planes has been developed for imagery and signals intelligence. Known as Unmanned Aerial Vehicles, these drones are a force multiplier by giving the battlefield commander an "eye in the sky" without risking an pilot. The US Army is significantly increasing the size of its current UAV force as part of the Future Combat System initiative.

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See also

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