There's a good chance that a surveillance satellite is taking pictures of your neighborhood right now, but you'll never know it's there. It's way too high above the Earth's surface to be seen by the naked eye. But there's something here on the ground that helped develop those satellites into the highly precise watching devices they are today: eye charts.

Back in the days before satellites — and even when satellites were fairly new — the military used planes like the U-2 and the SR-71 Blackbird to take pictures of the Earth's surface. But how could analysts tell how large something in a grainy black and white photo was? Easy. The spy planes took pictures of paved calibration marks first.


There are still dozens of them, now mostly cracked, weed-filled asphalt pads on remote air bases in the Mojave Desert. The 1951 USAF Resolving Power Test Targets, as they are officially know, are typically 78 feet long by 53 feet wide, and painted with black and white bars of different sizes and orientations. Sometimes, an scrap aircraft was placed next to the target for further visual referencing.

The same pattern is used to callibrate telescopes and scanners today, but for the most part is obsolete. High resolution digital satellites use focusing targets better suited to computer analysis. But the old spy plane eye charts aren't going anywhere, especially since most of them are located in those super secret desert restricted areas where the government stores cryogenically frozen alien warriors.

Photo credit: Google Earth via the Center for Land Use Interpretation