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 data using airplanes, helicopters, unmanned aerial vehicle, UAVs, Balloon (aeronautics), balloons, or other aerial methods. Typical data collected includes aerial photography, Li ...

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

Casa Grande, Arizona Casa Grande (O'odham language, O'odham: ''Wainom Wo:g'') is a city in Pinal County, Arizona, Pinal County, approximately halfway between Phoenix, Arizona, Phoenix and Tucson, Arizona, Tucson, in the U.S. state of Arizona. According to the 2020 ...

, 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; ) is a civilian foreign intelligence service of the federal government of the United States tasked with advancing national security through collecting and analyzing intelligence from around the world and ...

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 or disease responsible for the COVID-19 ...

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 cartography, 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 th ...

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 develope ...

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. 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 (also known as water withdrawal, water abstraction, and water intake) 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 ex ...

. 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, Pinal County, Arizona, United States, approximately northwest of Tucson, Arizona, Tucson and about southeast of Phoenix, Arizona, Phoenix. According to the 2020 United States census, 2020 census, the p ...

. , 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 () is a hot desert and ecoregion in North America 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 and California). It ...

. 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

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
{{National Reconnaissance Office 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