The National Aeronautics and Space Administration launched the first Earth-orbiting satellite to gather data on Earth’s natural resources and to provide detailed maps of the United States. The Landsat program provided unprecedented coverage of Earth’s natural resources and changing environmental conditions.
On July 23, 1972, the Earth Resources Technology Satellite (ERTS), more commonly known as Landsat 1, was carried into space aboard a Delta launch vehicle. ERTS began its journey from Vandenberg Air Force Base, California, and was placed in an orbit that would carry it over both the North and South Poles. This gave its special sensors an opportunity to scan every square mile of Earth’s surface.
The Landsat system began as a concept developed by William T. Pecora of the U.S. Geological Survey
While photography from high-flying aircraft provided a great deal of detail about the landscape below, it would require more than thirty thousand photographs taken from an altitude of twenty kilometers to photograph the entire United States. It was reasoned that a single satellite orbiting nine hundred kilometers overhead could accomplish the same task with fewer than six hundred photographs.
Weather satellites were already giving a bird’s-eye view of the planet, but their black-and-white television cameras did not provide for any detail. Objects smaller than two kilometers across could not be seen, and since photographs were taken from directly overhead, no depth of field was provided. Photographs taken by the Gemini program astronauts as they orbited one hundred kilometers above Earth provided much greater detail. Information about the elevation of landmarks could be extrapolated from low-angle shots. By using these techniques, it would be possible to create extremely accurate relief maps of an area.
In 1970, the National Aeronautics and Space Administration (NASA) developed a series of satellites designed specifically to study Earth’s surface. Sensors on the satellites provide high-resolution images in the visible light spectrum as well as in the infrared spectrum (the part of the invisible spectrum below the red end of the visible spectrum, which gives a quantitative measurement of heat). Rather than taking conventional photographs and transmitting them down to receiving stations, the Earth Resources Technology Satellite transmits a stream of numbers, which are converted into images on the ground. The orbital path of ERTS carries the satellite on a north-to-south path over the United States during early daylight hours. Its orbit is Sun-synchronous—that is, its path moves easterly at the same rate at which Earth rotates. The local solar time on any pass is thus identical for any degree of latitude. The equator is overflown at approximately 9:30
A mock-up of the Earth Resources Technology Satellite, first launched in 1972. It was later named Landsat.
Through a complex optical system aboard the 950-kilogram spacecraft, Earth’s surface is broken into narrow slices or scan lines. Landsat’s multispectral scanner system consists of three high-resolution television cameras that obtain the images in red and green light, as well as the near-infrared region invisible to the human eye. A mirror directs Earth’s reflected light from the east or west, sending scan lines into detectors. Each scan line is subdivided into individual segments seventy-nine meters by seventy-nine meters in size. The stream of numbers is transmitted to Earth, where it is assembled into an image by a computer. The images can be black and white, red or green, or “false color.” These “color” images require about six million bits of data, which can be manipulated to show healthy vegetation in bright red and diseased or insect-infected plants in gray. Unusual or unique combinations of reflected light levels can be intensified by computers to reveal features and trends on Earth’s surface not readily apparent to the human eye.
Built on the technological lessons learned from Landsat 1, the second Landsat joined it in orbit on January 22, 1975. Almost identical in size and capability, Landsat 2 was placed in an orbit synchronous with its twin so that virtually every point on Earth’s surface could be scanned every nine days. On March 5, 1978, Landsat 3 was placed into orbit. By this time, Landsat 1—having long outlived its design life—had failed, reducing repetition of coverage to once every eighteen days. Landsat 3 worked in conjunction with Landsat 2 to provide the desired viewing coverage.
Landsat was the first in a series of Earth-observatory satellites. The success of the first three Landsats led to the development of more powerful detectors. Landsat 4, launched July 16, 1982, carried a thematic mapper to image Earth and detect geological features of interest in mineral exploration. The mapper, with its one hundred imaging detectors, has better resolution capabilities than previous detectors. It can provide thirty-meter resolution versus the eighty-meter resolution of the multispectral scanner system. It images in seven spectral bands versus four and is faster because it sends data directly to Earth rather than storing it for later transmission. This direct link is provided by two satellites in the Tracking and Data-Relay Satellite System
The loss of Landsat 6 in October, 1993, was a major disappointment. It was launched from Vandenberg Air Force Base atop a refurbished Titan 2 missile left over from the Cold War. Shortly after the satellite separated from its booster, telemetry was lost. It was not determined whether the spacecraft malfunctioned or was destroyed in a transfer-stage mishap. The program regained momentum with the successful launching of Landsat 7 in April, 1999.
The Landsat system has provided unprecedented coverage of Earth’s natural resources and changing environmental conditions. Uses have included forestry, range management, water and marine resources, environmental monitoring, land-use planning, and mapping. Geologists study linear features on Earth’s surface that are possible geological faults. These lines may indicate mineral, oil, and groundwater locations, and even earthquake zones. Companies that explore for minerals and petroleum use the Landsat images to find ways of saving time and money. Agricultural experts identify several crops with a high degree of accuracy in fields as small as a few square meters. Firefighters have used up-to-date images of raging forest and brush fires to develop their plans of attack. When natural disasters strike, satellite imagery is used to assess damage.
Environmental uses and abuses have been closely monitored by Landsat. The widespread extent of clear-cutting in heavily forested regions of Oregon was not known until Landsat 1 images revealed its scope. Pictures from the Landsats have shown that industrial pollution has a far-reaching effect on the entire environment. Steel mills and power plants in one part of the country can cause acid rain in rural towns hundreds of miles away.
During the Persian Gulf War in 1991, Landsat images of Kuwait were used to show the extent of the damage to that nation’s oil fields inflicted during occupation by Iraqi forces. The massive clouds of black smoke from nearly six hundred burning oil wells could be clearly seen in the pictures.
The combination of figures on crop acreage computed from Landsat images with yield estimates derived from meteorological data help the Department of Agriculture accurately forecast harvests on a global scale. These data can then be used to direct the farming of essential crops and result in better use of the landscape.
The technology and techniques developed in the Landsat program have led to other Earth-observation satellites. Seasat,
The Earth Radiation Budget Satellite
Two other Earth-observation experiments flown on STS-41-G, as well as on other shuttle flights, were the Measurement of Air Pollution from Satellites
The space shuttle carried on the tradition, started with the Skylab program, of systematically collecting information about Earth’s land, sea, and air through the use of the shuttle-based research laboratory known as Spacelab.
A new era in Earth observation began with the deployment of the Upper Atmosphere Research Satellite
The decision to observe Earth on a regular basis from spaceborne observatories has led to the raising of the collective consciousness regarding this fragile planet. Scientists are able to observe the interaction between nature and humankind and to make suggestions about how to preserve Earth’s resources. This information can be used to improve the habitability of Earth and to provide a safe haven for future generations.
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Bodechtel, Johann, and Hans-Gunter Gieroff-Emden. The Earth from Space. New York: Arco, 1974. Fine collection of color photographs of Earth taken by manned and unmanned spacecraft. Discusses the history of space photography from the first crude black-and-white image transmitted from the orbiting Explorer 6 satellite in 1959 through the portraits taken by the crew of Apollo 17 as they journeyed from the Moon. Addresses the technical aspects of space photography. -
Brunn, Stanley D., Susan L. Cutter, and J. W. Harrington, Jr. Geography and Technology. Boston: Kluwer Academic, 2004. Examines the role of technology in geography and how various geography-related technologies have affected society. -
Johnston, Andrew K. Earth from Space: Smithsonian National Air and Space Museum. Buffalo, N.Y.: Firefly Books, 2004. Amazingly sharp photographs reveal how humans have altered Earth’s atmosphere and surface. -
Short, Nicholas M., et al. Mission to Earth: Landsat Views the World. Washington, D.C.: National Technical Information Service, 1976. This book, filled with images transmitted by the Landsat spacecraft, was designed to be used in a classroom and provides a teacher’s reference. Includes dozens of color and false-color images of Earth, bibliography, and index. -
U.S. Congress. House. United States Civilian Space Programs, 1958-1978. Vol. 1. Washington, D.C.: U.S. Government Printing Office, 1981. In a very concise report, the Committee on Space Science and Applications presents data compiled on all American space activity during its first two decades.
Skylab Inaugurates a New Era of Space Research
Global Positioning System Becomes Operational
Tracking and Data-Relay Satellite System Revolutionizes Space Communications
Endeavour Maps Earth from Space