The EROS of Landsat
THE FEDERAL GOVERNMENT'S LANDSAT PROGRAM is the most literal embodiment of remote sensing. Since launching its first satellites in the 1970s, Landsat has given us the first complete set of images of the entirety of the earth’s land surface, at a technically consistent scale—and has been doing it repeatedly, scanning the whole planet a couple of times a month, continuously, for more than 50 years.
This has led to a heap of data—many millions of images—managed and stored at the Earth Resources Observation and Science (EROS) Center, Landsat’s home near Sioux Falls, South Dakota, which became the largest civilian archive of remotely sensed imagery in the world. EROS’ function is to help operate the Landsat program, and to manage the flow of data: to ingest it, process it, store it, and make it available, to scientists and to the global public, for free. And more than that, to make it relevant and useful.
With no other uniform system of earth observation imagery operating so thoroughly and for so long, what Landsat uniquely offers is the ability to show changes to the planet’s surface over the last half a century, something that is increasingly useful not just to earth scientists, but as a record of anthropogenic change that is compelling to the citizens of the world at large.
Landsat’s Nine Satellites
EROS opened in 1973, soon after the launch of Landsat 1. While the CIA and Defense Department was leading the state of the art for earth imaging satellites in their own secretive ways, the idea of a civilian scientific earth observation satellite, what Landsat would become, was being considered since the early 1960s, when Apollo astronauts took useful photographs of the earth’s surface out the windows of spacecraft. Landsat was given a major nudge into existence by Interior Secretary Stewart Udall in 1966, when he announced the Department’s plan for the Earth Resources Observation Satellite, and the first version of the acronym EROS was coined.
A high-ground turf war of competing and conflicting factions within the federal government slowed the process, which was resolved by an agreement for sharing the program between NASA, the agency behind most civilian satellite programs, and the USGS, the nation’s earth resources information manager and map maker.
In 1969 NASA had enough money secured to officially solicit proposals for what was then called the Earth Resources Technology Satellite (ERTS). The proposals, for a new set of sensors and data recorders based on existing satellite program platforms, came in from RCA, using its Tiros weather satellite platform; GE with its Nimbus weather satellite platform; TRW with its Orbiting Geophysical Observatory platform; and Lockheed Martin, with a modified version of one of its reconnaissance satellite platforms.
Of these, two were selected to compete: GE and TRW. TRW subcontracted IBM to do the image data processing, using an innovative yet complex system. GE chose a simpler and less expensive method, with Bendix as the contractor. GE won the contract, followed by a bit of a protest from TRW, and built the satellite at its Space and Technology Center in Valley Forge, Pennsylvania.
The primary imaging sensor system used on this first Landsat was RCA’s Return Beam Vidicon sensor, a proven analog system using tubes to capture reflected green, blue, and red bands of visible light. A second system was also installed, using an unproven multispectral scanning technology, MSS, developed by Hughes Aircraft in California, capable of capturing infrared frequencies in addition to the visible bands, and at much lower weight and cost than RCA’s system. This proved significant when RCA’s system failed after a month, and the MSS system not only saved the satellite, but was an improvement in image quality. The added infrared bands showed vegetation well, and became standard in remote sensing after that. The inventor of the MSS scanner, a pioneering engineer named Virginia Norwood, became known as the Mother of Landsat.
Landsat 1 was ten feet tall and five feet wide, without its solar panels extended, and weighed about a ton. It was launched from Vandenberg Air Force Base in 1972, and operated beyond its designed life of five years, until 1978, when it was taken out of service, when its data recorders, which used magnetic tape, malfunctioned. But it was a success, and produced more than 300,000 images, which were safely beamed back to earth as data, and processed and stored at EROS.
Landsat 2 was launched in 1975, shortly before the program name changed from ERTS to Landsat, and was very similar to Landsat 1. Same with Landsat 3, launched in 1978. Landsat 4, launched in 1982, was the first of the second generation of Landsat, with an updated MSS, and a thematic mapper sensor, both built by Hughes. It also updated the World Wide Reference System to a new standardized scanning path and row process, making data sharing with other systems easier. Landsat 4 was built by GE AstroSpace, in the former RCA satellite plant in East Windsor, New Jersey, after GE bought RCA. Landsat 4 was also operated by NOAA, reflecting temporary changes at the federal level. It operated until 1993.
Landsat 5 was launched in 1984 and was similar to Landsat 4, except that it lasted much longer than its three-year designed life, staying operational until 2013, generating 2.5 million images over its 29 years. A good thing too, since Landsat 6 never made it to orbit. The only failure in the Landsat program, so far.
This was a symptom of a tough period for Landsat, its dark days, if you will, which began in the late 1970s, when its costs, around one billion dollars a year, relative to its minimal financial gains, were being challenged. In 1979 President Carter transferred Landsat operations from the Interior Department’s USGS to NOAA, part of the Commerce Department, with a mandate to explore ways for it to generate more income, including being privatized. President Reagan accelerated the process, and fees for images soared, from just a couple of hundred dollars to more than $4,000 per image, putting it beyond reach of most people and organizations, cutting its revenue even more.
The order to privatize Landsat came in 1984. Two companies bid for the contract: Eastman Kodak and EOSAT, the newly formed Earth Observation Satellite Company, jointly run by Hughes and RCA. EOSAT won the contract in 1985, and henceforth EROS would do the work, and EOSAT would take the proceeds. Privatization also complicated the design and launch of the next satellite, Landsat 6. It was supposed to be launched by the Space Shuttle, but after the loss of the Challenger in 1986, that idea was scrubbed.
Landsat 6 was the first Landsat fully intended to be a commercial product. It was built by Martin Marietta, which had by then purchased GE AstroSpace, including its satellite plant in East Windsor, New Jersey. The primary sensor was an Enhanced Thematic Mapper, made by Hughes’ Santa Barbara Research Center.
Landsat 6 was finally launched from Vandenberg in 1993, and soon after launching and separating from the main booster, it encountered a fuel problem, and never reached orbit. Contact with the satellite was lost, and it is assumed to have crashed into the Indian Ocean.
Challenges to the privatization of Landsat mounted, and congressional hearings were held. Terms for a phase-out of EOSAT, and a return of the program to the USGS, were established in the mid-1990s, ending the ten years of private control.
Landsat 7 launched in 1999, with significant upgrades. Built by Lockheed Missiles and Space, using the Tiros N weather satellite platform, it has solid state memory and a transmission rate capable of 532 images per day. It uses an Enhanced Thematic Mapper sensor, with eight bands, including red, blue, green, near-infrared, mid-infrared, and thermal infrared. The color balancing of its images became the standard for satellite imagery we are now familiar with, through its use in popular programs like Google Maps.
25 years later, Landsat 7 was still capable of providing images, though its orbit has been degraded, and its fuel limited. It was put in standby mode, following the 2021 launch of Landsat 9, which has occupied its orbit. Landsat 7 is expected to receive its final commands by May 2025, shutting it down forever. Like Landsat 1 through 5, Landsat 7 will remain in orbit for decades, circling the globe as inert waste, eventually dropping low enough to burn in the upper atmosphere.
Landsat 8 was launched in 2017, the fourth generation of Landsat, with major upgrades, and is still fully operational now. It was built at the Orbital Science Corporation plant in Gilbert, Arizona, and has two primary sensors. One sensor, called the Operational Land Imager (OLI), captures reflected light from nine spectral bands, five for visible light, and four for infrared. It was built by Ball Aerospace in Boulder, Colorado. The other sensor, called the Thermal Infrared Sensor (TIRS), measures heat, using two spectral bands. It was built by the NASA Goddard Space Flight Center in Greenbelt, Maryland. Landsat 9, launched in 2021, is similar to Landsat 8, but with updated OLI and TIRS sensors. Landsat 9 was built in Gilbert, Arizona, too, though by Northrop Grumman, which bought Orbital in 2018. Three new and smaller Landsat satellites are being designed, for possible launch in 2030.
Data Flow and Management at EROS
Despite improvements in sensor and data management technology over the decades, the orbiting and scanning behavior for all Landsat satellites was like that of Landsat 1. After launching from Vandenberg Air Force Base (now Space Force Base), on the west coast of the USA, the satellites follow a sun-synchronous polar orbit. Circling the globe at around 17,000 miles an hour, the satellite makes one loop every 99 minutes or so, with the globe rotating beneath it. At an altitude of around 430 miles above the surface, sensors scan a swath around 115 miles wide, each slightly overlapping the previous one, and complete a full set of images of the planet after 251 orbits, every 16 days.
Landsat 8 and 9 are circling the planet together, each generating around 750 images a day. Their data is streamed down to earth as it is being collected, and stored on on-board memory, which is erased once the downloaded data is securely processed and stored. The satellites stream the data when they are passing over one of the antenna ground stations, which are located around the globe, so the satellites and stations can be in constant contact.
There are five primary ground stations serving Landsat 8 and 9, each with a three-letter code name. SGS is at the massive SvalSat facility in Svalbard, Norway, which is the largest satellite earth station in the world, with around 100 antennas, used by commercial and government clients from all over the world; ASN, at the Geoscience Australia facility in Alice Springs, Australia; NSN, located in Neustrelitz, Germany; GLC, at the NOAA facility in Gilmore Creek, Alaska, near Fairbanks; and LGS, the ground station at EROS, near Sioux Falls. There are other commercial and governmental ground stations, utilized by other NASA programs, that have been used in the past, and could be used in the future.
The way in which the data from ground stations gets to EROS has evolved over the years. It used to be stored on film and reels of magnetic tape that were shipped by trucks and airplanes, even through the US mail. Later it was conveyed through satellite-based communication networks. Now it goes through the internet. The data is also simultaneously sent to the Landsat Mission Operations Center at NASA’s Goddard Space Flight Center in Maryland, which is the primary control center for the satellites. (There is a backup satellite operations center at EROS, capable of running the system if there is some kind of significant failure at Goddard.)
The process for getting imagery to EROS, and managing it once it’s there, involves most of the 650 or so people who work there. As with other federal programs, many of those people are contractors—just 120 people at EROS are federal employees. The main contractor at EROS used to be Hughes, then Raytheon. It is now KBR, a company with a bit of a notorious history. Once known as Kellogg, Brown, and Root, KBR was part of Halliburton for decades, doing military field and infrastructure work of all kinds in war zones. KBR, still based in Houston, is now one of the primary technical support contractors for NASA, and for the USGS, too.
EROS needs a lot of technical support, as it is above all, an image-processing megacenter, with more than ten million images—74 petabytes worth, and growing. Managing and processing this image data is a highly technical activity, and involves powerful supercomputers.
The first big computer installed at EROS was a Burroughs 6700 mainframe, in use from 1976 until 1985, when it was replaced by a VAX computer, from the Digital Equipment Corporation. Since then EROS has mostly used supercomputers made by Cray, replacing them every five to ten years. In 2019 the Denali and Tallgrass computers arrived, from Cray, named after national natural landmarks. In 2023 another computer, called Hovenweep, went online, next to Denali. It is the Interior Department’s most powerful supercomputer.
The supercomputers are in Computer Room 2 at EROS, and are used for processing. Computer Room 1 is more about data storage, and has been used for things like robotic retrieval machines that feed libraries of tape and cartridge drives into mainframes. After years of scanning and organizing, most of EROS’ images are stored on hard drives and tape cartridge drives, copies of which have been sent to the National Archives. In addition, as of 2022, EROS images are stored in the cloud, through a contract with Amazon Web Services. Although backed up at various locations, EROS’ mission includes preserving the source material on-site here, too, which it does in several rooms at basement level.
When Landsat began in the 1970s, images mostly came as a stream of data, stored on magnetic tape, and the archive at EROS now stores thousands of reels of tape, in a variety of formats, from big spools to more contemporary linear tape cartridges. It also stores film and negatives from a wide range of sources, including the National Aerial Photography Program and the National High Altitude Photography Program, images used to make all those USGS topographical maps. And EROS has all of those topo maps, too, and every other map generated by the USGS, along with 1.2 million images from the Bureau of Land Management, another Department of the Interior agency.
Much of what is stored here is part of the National Satellite Land Remote Sensing Data Archive, which includes all the Landsat imagery, as well as that of some commercial satellite programs, such as SPOT and GeoEye. The archive also includes nearly a million declassified photos from the Corona, Argon, and Lanyard spy satellite programs, which ran from 1960 to 1972. Using high-quality optics and wet film photography, exposed film cartridges were dropped from space with a parachute, caught by aircraft, and turned into photographs.
Corona was part of the Keyhole series of space-based surveillance satellites, some with resolution down to half a meter. Though systems like this were not available at the time Landsat was being designed, as they were classified until the 1990s, high-resolution photography was not considered optimal for Landsat anyways. Earth imaging for Landsat used a broader brush, typically 30 meters of resolution, enough to see the patterns of buildings, foliage, waterways, and other contours of the land, without creating prohibitively large image file sizes. Progress with surveillance systems continued in their own way, getting more and more detailed, while Landsat continued along a consistent track, making moderately detailed images that were compatible over a half a century, and revealing a bigger picture.
EROS as a Public Facility
One of the remarkable things about the EROS Center is where it is, in gently rolling agricultural land 15 miles north of Sioux Falls, in part practical, political, and poetic. It was thought, initially, that it would be important to house the facility in the middle of the nation, so that it was within the range to receive data from satellites as they flew over any part of the country. While the acceptable middle was a relatively large area of the central plains, from northeast Kansas to southwestern Minnesota, politics came into effect to further narrow the location down, first to South Dakota, then to Sioux Falls.
While the need for being in the middle diminished as technology evolved (such as the ability to store the data on-board through tape memory and download it later, rather than through a continuous stream) it seemed important for this collection and control center to be in the middle of the country symbolically, too. Landsat is, after all, one of the crowning achievements of the USGS, America’s mapping agency, and the Department of the Interior, manager of the American Land. If you had to put one pin on the 1:1 scale map of the country, it should probably be in the middle.
Another remarkable thing about EROS is that it is open to the public with open arms. Anyone can come any time during business hours. After a fairly thorough vehicle check out at the security booth (looking in the trunk and under the hood, and inspecting the undercarriage with a mirror, de rigueur for many federal facilities these days), visitors proceed up a curving road to the parking lot and the main entrance.
The lobby and adjacent atrium were built as part of an upgrade to EROS in 1996, which added 65,000 square feet to the facility. This came at a time of rebirth for Landsat, after the decade of privatization, dwindling funds, and the failed launch of Landsat 6. The nine-million-dollar upgrade was in anticipation of Landsat 7, and new initiatives to manage and distribute data to end users, including the Land Process Distributed Active Archive Center, which is part of the new wing. Room was also made for more computers, and more storage.
Inside the lobby is a 360-degree reception desk, with free information and take-aways, where any questions are entertained by staff. And if they can’t be answered, why not take a guided tour, available at 10AM and 2PM, every day? Most visitors will have a hard time coming up with questions, though, given the extent of the information displays on tap.
The lobby is a cavernous visitor hall, replete with touchscreens of staggering depth and dimensions, blending images and information, embedded in a matrix of real-earth-colored aerial imagery, all produced in-house. There are only two three-dimensional objects on display: a 1:3 scale model of Landsat 8, hanging from the rafters, and a five-foot-wide rotating globe, surrounded by an orbit of touchscreens.
Along the atrium’s walls are more text and image panels, following the same style guide, explaining more about how Landsat works, what resources are stored at EROS, how images are interpreted, and what they reveal.
There is also an exhibit of aerial scenes printed on squares of stretched canvas. A title panel at the beginning explains that this exhibit is called Earth as Art 6, and features images from Landsat and the EROS archives that were selected because their “colors, patterns, textures and shapes all make for intriguing artwork as seen from the perspective of space.” It includes 20 images with titles such as Torn Apart, Painting the Desert, and Deep Blue Cubism. Each image is explained in a brief caption, stating when the scene was captured, where on earth it is located, and what is going on.
This is the latest of six Earth as Art exhibits, curated by a small and changing group of EROS staff, since 2001. While the images mostly depict alluring patterns formed by natural forces, such as water flow and land erosion, many also depict human forces at work in the colorful sworl, too, suggesting that the exhibit is more than just an exploration of form. And rather than being conclusive, the selections allude to the limitless possibilities that exist within the archive of images at EROS, available to all, to curate our own portraits of the planet.
Perhaps the most remarkable thing about EROS is that it is still there at all, as it has been contributing to its own obsolescence from the beginning, in 1972, when Landsat was the only thing of its kind out there.
In 2008 there were around 150 earth observation satellites in orbit. Today there are more than a thousand, including hundreds of small and effective cube-sat cameras that have been launched by Planet Labs, and the European Space Agency’s Sentinel-2 satellites, which collect images at higher resolution than Landsat, and renew every five days. The ease and frequency of getting high-quality observation systems in space is increasing exponentially.
Meanwhile, the archive at EROS, which has been busy digitizing its print and film-based material with innovative automated systems since the 1970s, has stepped up its digital distribution efforts even more since announcing its free and open data policy in 2008, declaring that all of its image resources are available to the world, for free. Much of its archive is now available through the internet, with more to come. EROS, like so much, is dissolving into the cloud.
These days, updating, maintaining, and improving an archive of images and information is all about managing online resources and data flow. Likely some are wondering why EROS’ work can’t be done by just a few KBR contractors, working from home.
But still: physicality persists. We are organic beings, dependent on Earth Resources, as well as each other. If EROS is about anything, it is about that. Hopefully it will remain forever in its physical form, at the heart of the national map, as an archive and temple to the physical landscape. ♦