SPIES IN THE SKY

From balloons to satellites, Earth is under constant surveillance from above

- ANDREW MAY

The topic of high-altitude surveillance hit the headlines in February this year, with the shooting down of what appeared to be a Chinese spy balloon by a US fighter plane. The balloon was large enough that it was easily visible from the ground, but in more subtle ways – using satellites, stealth planes and drones – covert observation from above is going on all the time, and has been for years.

The military value of large, crew-carrying balloons was recognised almost as soon as they were invented. They were employed during the French Revolutionary Wars of the 1790s, and again in the American Civil War of the 1860s, to gather valuable information about enemy activity that couldn’t be observed from ground level. Similarly, when powered aircraft were first used during World War I, one of their main roles was in the reconnaissance of enemy lines – initially using an observer with binoculars, and later employing cameras that took the first aerial photographs. By World War II, with the aid of onboard film-processing equipment, it was possible to analyse high-resolution images of the ground below in near real time.