dequalized:

There are dozens of aerial photo calibration targets across the USA, like this expanded tri-bar array at Fort Huachuca in Arizona, USA.

The Center for Land Use Interpretation reports that the curious land-based two-dimensional optical artifacts are used for the development of aerial photography and aircraft. They were made mostly in the 1950s and 1960s, though some apparently later than that, and many are still in use, though their history is obscure.

Aerial photo by Google Earth.