Casa Grande Photogrammetric Test Range
The Casa Grande Photogrammetric Test Range is a test range established in the mid-1960s to test the dynamic performance of aerial survey cameras. The range consisted of consist of 272 concrete calibration markers embedded into the Earth's surface in and around Casa Grande, Arizona, United States. The markers are commonly (and erroneously) believed to have been used to aid camera calibration for the US Central Intelligence Agency's Corona spy satellite program; in fact, they were used as references for aerial surveys through photogrammetry. The markers formed a square grid, and were maintained from  1959 to 1972. Some of the original markers can still be found on satellite maps and ground inspection. See links to maps below. Background. Following the launch of Corona satellites in the 1960s, the US National Foreign Intelligence Program determined that there was a need for calibration under the Controlled Range Network. Working with the Arizona Real Estate Office, the US Army Map Service was directed to lease land for office space in Casa Grande, Arizona. Land was leased in parcels, with access to a road. Large concrete Maltese crosses in the ground, each in width, were in place by  1967. The crosses were arranged in a grid. The cross-shaped patterns were used to calibrate aerial photography equipment for aircraft. The Corona satellite program used a different "tri-bar" calibration pattern. Each of the targets has a manhole on the west arm of the cross, the manhole has a cement cover and steel reinforcement bars. According to Gary Morgan, member of the Cold War Museum in Warrenton, Virginia, the six pieces of rebar, which protrude at an equal distance from each other, may have been used to hold a laser designator to provide the Corona satellites a more accurate  fix on each target. The majority of the targets were abandoned when the program ended in 1972. By the late-1970s, the US Army Map Service considered the targets to be obsolete for their use as the land on which they were situated had subsided because of groundwater extraction. Land lessees were then given the option of having the targets removed and dumped near Eloy, Arizona. , at least 143 targets remain in place, unless they have been removed because the location has been redeveloped. Images. The Casa Grande Calibration Targets pictured in the image gallery are two of the few remaining  ones in the Sonoran Desert. The first one is located on the southeast corner of South Montgomery and West Cornman Roads. The second one is located on the northeast corner of West Cornman Road and Carmel Boulevard. Links. Candy CORN: analyzing the CORONA concrete crosses myth *