It makes perfect sense. If you're the Air Force running spy planes, or the CIA launching surveillance satellites, you want to know how accurately your overhead cameras can perceive the ground below. And to do that, you need a simple sight test, not so different from the type optometrists give: Can you read this line? What about this line?
The Center for Land Use Interpretation (CLUI) reports that since the 1950s the U.S. military has indeed posed such resolution tests to its aerial spy fleet. They come in the form of 78-foot by 73-foot black and white patterns, painted on concrete or asphalt, usually somewhere on the grounds of military bases. As CLUI explains:
The pattern painted on the targets is sets of parallel and perpendicular bars duplicated at 15 or so different sizes, and, sometimes, a large white square...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.
These targets are found on military installations around country, but they're concentrated in the Mojave Desert and on nearby Edwards Air Force Base, where the A12, SR-71 Blackbird, the U-2 spy planes were tested. Geoff Manaugh at BLDGBLOG, who also blogged this story, did some searching in that area on Google Maps and found one of the targets, located here, without too much trouble.
The CLUI story explains that these targets have become largely antiquated because they were designed for film cameras and are not very effective at testing digital resolution. Even so, they are kind of awe-inspiring, a little creepy, and just one more example of the immense, parallel world that the military occupies.
GoogleEarth image of a standard tri-bar test pattern on the Photo Resolution Range at Edwards Air Force Base that has been greatly expanded. Image courtesy of Google and the U.S. Geological Survey via CLUI.
GoogleEarth image of a standard tri-bar test pattern off the runway at Walker Field, Maryland. Image courtesy of Google via CLUI.
GoogleEarth image of a tri-bar array at Eglin Air Force Base, Florida. Image courtesy of Google and the U.S. Geological Survey via CLUI
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Leon Neyfakh is the staff writer for Ideas. Amanda Katz is the deputy Ideas editor. Stephen Heuser is the Ideas editor.
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