- Car park-sized patterns used to calibrate lenses on planes and satellites
- Most built in the Fifties and Sixties at an unknown number of U.S. locations
- They have become obsolete thanks to new digital imaging systems
By DAMIEN GAYLE
These mysterious QR code-like patterns are painted across dozens of locations in the U.S.
Although they look rather similar to something you might be shown by an optician, they are not God’s equivalent to an eye test. They are meant for another kind of all-seeing eye.
The car park size patterns are used to calibrate the lenses of high-powered aerial and satellite cameras, of the kinds used by paranoid nations to keep an eye on their global rivals.
Of obscure origin, it appears that most of them were put in place in the Fifties and Sixties, as the U.S.-USSR superpower arms race led to the unprecedented fears of mutual annihilation.
Their existence has been highlighted by a recent newsletter by the U.S.-based Center for Land Use Interpretation, a group dedicated to researching ‘human interaction with the Earth’s surface’.
The calibration sites follow a general form established by the U.S. Airforce and Nasa, the CLUI notes.
Consisting of a concrete pad measuring 78ft by 53ft and coated in a heavy black and white paint, they are decorated with patterns consisting of parallel and perpendicular bars in 15 or so different sizes.
This pattern, sometimes referred to as a 5:1 aspect Tri-bar Array, is similar to those used to determine the zoom resolution of microscopes, telescopes, cameras, and scanners.
The targets function like an optician’s eye chart, with the smallest group of bars discernable marking the limit of the resolution for the camera being tested, according to the CLUI.
‘For aerial photography, it provides a platform to test, calibrate, and focus aerial cameras traveling at different speeds and altitudes,’ the CLUI adds.
‘The targets can also be used in the same way by satellites.’
California’s Mojave desert, a principal test location for U.S. surveillance aircraft like the SR-71 Blackbird and the U2, and more recently unmanned drones, is a resolution test target hot spot.
Mojave’s Edwards Air Force Base has the largest concentration of calibration targets of any spot in the U.S., with 15 running in a 20 mile line across the south-east side of the base.
This allows a single test flight to test aircraft surveillance instruments on all the targets without having to change course or loop back.
According to the CLUI: ‘There is some variation in the size and shape of the targets at Edwards, suggesting updates and modifications for specific programs.
‘A number of the targets there also have aircraft hulks next to them, added to provide additional, realistic subjects for testing cameras.
‘Some of these planes are themselves unusual and rare military jets, officially in the collection of the base museum, despite being left out on the range.’