If you’re flying above the US you might spot what looks like mysterious giant barcodes below.
Dotted across the landscape, mostly near airforce bases, they look like QR codes for aliens.
Spoiler alert: they aren’t.
Embossed onto a panel of tarmac, they’re certainly not long-lost relics from ancient civilizations either.
In fact, these giant barcodes only hark back to the 20th century
These monochrome markings were actually used to calibrate the lenses of aerial and satellite cameras
The vast majority were made in the 1950s and 1960s.
That’s when the Cold War was starting to get a little heated.
The giant barcodes are actually a hangover from a US attempt to bolster its aerial reconnaissance and the technology behind it.
Come back to earth and from the ground you’ll notice that they’re usually situated on a flat pad of concrete or asphalt.
The black and white symbols are put into organised lines.
These stripes were used by planes and satellites.
The aircraft used their optical resolution to calibrate their imaging equipment.
While it’s hard to get a sense of perspective from the air, they’re usually slightly smaller than a basketball court.
So how do they work?
“The targets function like an eye chart at the optometrist, where the smallest group of bars that can be resolved marks the limit of the resolution for the optical instrument that is being used,” say the Center for Land Use Interpretation (CLUI).
“For aerial photography, it provides a platform to test, calibrate, and focus aerial cameras traveling at different speeds and altitudes.
“The targets can also be used in the same way by satellites.”
It’s thought the targets were used to test formidable aircraft developed by the US during the Cold War period.
These aircraft include the SR-71 Blackbird and the U-2.
While they’re still in situ, modern technology doesn’t need to be calibrated in the same way.
So while there are still dozens of them lying across the landscape of the US – they’re no longer in use.
On the hunt for them?
They can be found near Eglin Air Force Base in Florida, the Nevada Test Site, Fort Huachuca in Arizona and Wright-Patterson Air Force Base in Ohio.
You can also look near Travis Air Force Base in California, Marine Corps Air Station Beaufort in South Carolina, and Shaw Air Force Base in South Carolina.
And this calibration technique wasn’t unique to the US.
In fact, internet sleuths were trawling Google Maps in 2011 and noticed strange structures in the Chinese desert.
Some were square, others zig-zagged, while a few consisted of giant characters from the Chinese alphabet.
While conspiracy theories abound, it was eventually revealed they were also there to calibrate China’s reconnaissance satellites.