by Damien Gayle Daily Mail
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.
A standard tri-bar test pattern off the runway at Walker Field, Maryland: These mysterious QR code-like patterns painted across dozens of locations in the U.S. are used to calibrate airborne and satellite cameras
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.’
A tri-bar test pattern on the Photo Resolution Range at Edwards Airforce Base in California: California’s Mojave desert is a resolution test target hot spot and is where many of the U.S.’s surveillance planes are tested
An expanded tri-bar array at Fort Huachuca, Arizona: 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
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.