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Across the USA you will find dozens of these strange markings painted on rectangular slabs of concrete and asphalt. They are known as aerial photo calibration targets, relics from the past that dot the landscape. They were made mostly in the 1950s and 60s, their form established by the US Air Force and NASA.
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. 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.
