The Casa Grande Photogrammetric Test Range is a test range established in the mid-1960s to test the dynamic performance of

aerial survey Aerial survey is a method of collecting geomatics or other imagery by using airplanes, helicopters, UAVs, balloons or other aerial methods. Typical types of data collected include aerial photography, Lidar, remote sensing (using various visible ...

cameras. The range consisted of consist of 272 concrete calibration markers embedded into the Earth's surface in and around

Casa Grande, Arizona , settlement_type = City , image_skyline = Casa Grande-Casa Grande Union High School-1920-2.jpg , imagesize = 250px , image_caption = Historic Casa Grande Union High School which now serves as the ...

, United States. The markers are commonly (and erroneously) believed to have been used to aid camera calibration for the US

Central Intelligence Agency The Central Intelligence Agency (CIA ), known informally as the Agency and historically as the Company, is a civilian foreign intelligence service of the federal government of the United States, officially tasked with gathering, processing, ...

Corona Corona (from the Latin for 'crown') most commonly refers to: * Stellar corona, the outer atmosphere of the Sun or another star * Corona (beer), a Mexican beer * Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...

spy satellite program; in fact, they were used as references for aerial surveys through

photogrammetry Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant ima ...

. 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

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 The Army Map Service (AMS) was the military cartographic agency of the United States Department of Defense from 1941 to 1968, subordinated to the United States Army Corps of Engineers. On September 1, 1968, the AMS was redesignated the U.S. Army T ...

was directed to lease land for office space in

. Land was leased in parcels, with access to a road. Large concrete

Maltese cross The Maltese cross is a cross symbol, consisting of four " V" or arrowhead shaped concave quadrilaterals converging at a central vertex at right angles, two tips pointing outward symmetrically. It is a heraldic cross variant which developed f ...

es 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 A manhole (utility hole, maintenance hole, or sewer hole) is an opening to a confined space such as a shaft, utility vault, or large vessel. Manholes are often used as an access point for an underground public utility, allowing inspection, m ...

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 A laser designator is a laser light source which is used to designate a target. Laser designators provide targeting for laser-guided bombs, missiles, or precision artillery munitions, such as the Paveway series of bombs, AGM-114 Hellfire, or ...

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 Water extraction (or water withdrawal) is the process of taking water from any source, either temporarily or permanently, for flood control or to obtain water for, for example, irrigation. The extracted water could also be used as drinking wate ...

. Land lessees were then given the option of having the targets removed and dumped near

Eloy, Arizona Eloy is a city in Pinal County, Arizona, United States, approximately northwest of Tucson and about southeast of Phoenix. According to the U.S. Census estimates in 2019, the population of the city is 19,625. History In 1880, as tracks were ...

. , 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 Sonoran Desert ( es, Desierto de Sonora) is a desert in North America and ecoregion that covers the northwestern Mexican states of Sonora, Baja California, and Baja California Sur, as well as part of the southwestern United States (in Arizona ...

. 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.

References

{{Coord, 32.76265, -111.73853, format=dms, type:landmark_region:US-AZ_dim:20000, display=title

Links

Candy CORN: analyzing the CORONA concrete crosses myth
All Corona Satellite Calibration Targets
- Google map of the locations of all targets, identified as Present, Damaged, or Missing.
Remaining Corona Satellite Calibration Targets
— Google map of 145 remaining markers which formed a grid, used from 1959 to 1972 to calibrate the Corona spy satellite cameras, by Andrei Conovaloff, 2018.
3 online reports
''Arizona Republic'', July 2, 2016. — "Corona spy satellite timeline"; "How Casa Grande crosses calibrated spy-satellite camera"; "How Casa Grande crosses helped fight the Cold War".
NPR
National Public Radio, October 11, 2016. - "Decades-Old Mystery Put To Rest: Why Are There X's In The Desert?"
All points in OpenStreetMap
Casa Grande, Arizona National Reconnaissance Office 1960s establishments in Arizona Buildings and structures completed in the 1960s Photogrammetry Abandoned buildings and structures

Background

Images

See also

References

Links