Two artists explore spy satellite calibration markers in the desert — and trace the satellites in the sky today.

Spy satellite calibration target, from "Ground Truth: Corona Landmarks."
Hover over the image to magnify the names of satellites. Calibration Mark AC48 with Satellites, from Ground Truth: Corona Landmarks.

In the Sonoran Desert south of Phoenix, Arizona, there is an array of giant concrete targets whose purpose was secret until about a decade ago. Each target is made of four triangular slabs that form an X about 60 feet wide. If you were to stumble across one of these strange monuments on a desert ramble, you would not see it as part of the larger array, as the targets are spaced a mile apart on a 16×16-mile grid. You might guess that it was meant to be seen from above, like the concrete arrows that guided navigation for U.S. airmail pilots, but in fact these mysterious Xs are conspicuously missing from flight maps.

They are ground-truth markers for calibrating the first spy satellites, under a Cold War program known as Corona. Installed in the mid-1960s by the U.S. Army Corps of Engineers, the targets were left to ruin when the program was decommissioned in 1972. They were forgotten until 2004, when pilot Pez Owen traced the strange symbols she had seen from the air to the Corona program. 1

The declassified 16mm film A Point in Time tells the story of how the CIA and Air Force raced to build a space-based surveillance system after the launch of Sputnik. It must have seemed preposterous at the time: panoramic cameras filled with pounds of physical film were shot into space to take pictures of the Soviet Union and China, and then the records were sent back to Earth for analysis in heat-shielded capsules that fell through the atmosphere, shedding layers and unfurling parachutes caught by planes. After years of failed attempts, the plan actually worked.

Map of calibration targets, from "Ground Truth: Corona Landmarks"
Map of spy satellite calibration targets in the Sonoran Desert. [Interactive map by Damon Sauer]

With my colleague Damon Sauer, I have been exploring this array of ground-truth markers for the past several years. They are off Interstate 8, near the earthen building ruins of Casa Grande, interspersed among truck stops, quarries, alfalfa fields, and canals. Damon mapped the entire system, using images from Google Earth and historic aerial photographs, and we are visiting the surviving targets on foot. Our project inverts the original relation between the ground and outer space. While the Corona markers were meant to be seen from above, we have turned them into observatories for perceiving the invisible bodies in orbit today.

We plot the location of all publicly known satellites that were overhead at the moment the photograph was taken. Our images are thus documentary records, aesthetic statements, and data maps, all at once. If you look closely, you can read the names of the satellites. Some are evocative, like “Globalstar” and “Cosmos,” while others indicate the purpose or country of origin. We were astonished by the number of satellites present in the sky at any given time (an emerging sustainability issue, as myriad metallic flecks encircle the globe).

“Ground truth” is a term used in remote sensing to describe the correspondence between image data and physical features in the world. We were drawn to the term because it honors embodied or situated knowledge as a special kind of awareness, while also evoking photography’s tenuous relation to truth. Our project examines the relation between human beings and the pervasive information networks in which we are enmeshed. Our satellite tracings resemble star charts as old as civilization — a reminder that humans have always sought to orient themselves to the heavenly unknown.

Ground Truth: Corona Landmarks

Authors’ Note

The photographic project “Ground Truth: Corona Landmarks” is supported by the Land Arts Mobile Research Center/Andrew W. Mellon Foundation.

  1. The earliest account of Pez Owen’s discovery is in an USACE newsletter: Mike Tharp, “X Marks the Spot(s),” The Newcastle, Vol. 34 No. 6, Sept 2004, US Army Corps of Engineers Los Angeles District. See also Scott Craven, “How Casa Grande Crosses Helped Fight the Cold War,” The Arizona Republic, June 24, 2016; and Danny Hajek, “Decades Old Mystery Put to Rest: Why Are There X’s in the Desert?,” National Public Radio, October 11, 2016.
Julie Anand and Damon Sauer, “Skywatching,” Places Journal, May 2017. Accessed 01 Oct 2023.

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