ES 351, ES 771, ES 775
|Technical characteristics||Image processing|
In the past, the only way to investigate a given area was through direct observation and sampling on the ground and from ships or aircraft. Many portions of the globe are inaccessible and were poorly known. Observations were mainly limited to those features that could be seen, photographed, or measured in visible portions of the spectrum. Local studies were compiled to provide regional interpretations of environmental conditions. However, it was difficult if not impossible to obtain global interpretations or to document changing conditions over large areas.
Many people now take for granted the daily images of clouds collected by weather satellites, but such routine viewing of the Earth from space is relatively new. Scientist and writer, Arthur C. Clarke (1917-2008), first proposed in 1945 that satellites in geosynchronous orbit above the equator could provide global communications links. Subsequently in 1951, he proposed that a satellite in a polar (N-S) orbit could allow humans to systematically view the whole planet, as the Earth rotated beneath the satellite (Lauer et al. 1997). The first photographs taken by astronauts and early satellite images began to change our concept of the Earth in the 1960s, and remote sensing of the Earth's surface has been continuous ever since. Viewing the Earth from space leads to a powerful impression: the Earth is an integrated, complex, dynamic system that is unique so far as we know.
A great many satellite systems have been designed and operated during the past three decades. NASA's Goddard Space Flight Center in Maryland has taken the lead in developing experimental satellite technology for scientific observations of the Earth. Once a satellite system is deemed operational, it is turned over to another governmental agency or to a private company for routine operation.
|Left: entrance to NASA Goddard Space Flight Center in Greenbelt, Maryland, just outside Washington, D.C. Right: antenna originally used for Apollo missions and then reconfigured for Landsat.|
|Left: clean room for assembly of satellite components. Wall of air filters on right; note tool boxes and exit door to left for scale. Right: chambers for testing satellite components under extreme conditions. Photos © J.S. Aber.|
|Harrisburg, central Pennsylvania. This synoptic view depicts the Appalachian Mountains. The Piedmont province is visible in lower right corner. The Great Valley runs SW-NE across center of view, and the Valley and Ridge province occupies the NW portion of scene. The city of Harrisburg is the light blue patch next to the Susquehanna River in lower left corner. Landsat TM bands 2,3,4; acquired 11/84; image from NASA GSFC.|
|Infrared image of Mount St. Helens volcano about four years after its major eruption in 1980. This image is a composite of mid- and thermal-infrared bands. Red shows active vegetation, and green/blue are bare rock and soil. The bright pink/white spots indicate zones of high heat flow (hot soil/rock). Landsat TM bands 6,7,6; acquired 7/84; image from NASA GSFC.|
The scanner did have one important advantage, its multispectral capability. Agricultural research had demonstrated the value of multispectral imagery. For example, the 0.63 to 0.68 µm band measures chlorophyll absorption; the 0.79 to 0.9 µm band indicates water content in leaves; and the 1.55 to 1.75 µm band displays soil moisture. Norwood's group initially designed a six-band scanner for the satellite. NASA's small satellite could not house the large scanner, however, so a more modest four-band multispectral scanner or MSS was built. The spectral bands were chosen in actuality to simulate false-color infrared photography (Mika 1997). The Apollo 9 mission in 1969 included an photographic experiment in which four coaxially mounted cameras were used to simulate multiband imagery of the MSS; the results provided a proof of concept for the technology (Lowman 1999).
The debate about using RBV cameras or a scanner was intense (Hall 1992). NASA finally compromised and put both systems on the satellite. On July 23, 1972, the first Earth Resources Technology Satellite (ERTS-1) was launched at Vandenberg Air Force Base in California. Within hours the first MSS images created a sensation with their amazing clarity and synoptic views of the landscape. Meanwhile, the RBV cameras were afflicted with an "unexplained electrical problem" and were quietly shut down a month later.
|Original Landsat MSS instrument on display at the National Air and Space Museum in Washington, D.C. This was a duplicate instrument built for ground testing and trouble-shooting. Photo © J.S. Aber.|
ERTS-1 MSS ushered in an era of previously unimagined synoptic knowledge of the Earth. Images revolutionized all types of cartographic and environmental studies of the Earth (Williams and Carter 1976). This huge success led to funding for two more nearly identical satellites in 1975 and 1978, and the program was renamed Landsat in 1975. MSS was an experimental system that far exceeded its designers' most optimistic expectations, not only in data quality but also in the large user community that developed. NASA benefitted greatly from the early Landsat program, at a time when its manned-spaceflight mission was in transition.
|Early Landsat MSS image depicting the area of south-central Saskatchewan, Canada, May 1978. MSS bands 1, 2 and 4 color coded as blue, green and red; active vegetation appears in pink and red colors. Old Wives Lake to left; Regina is the city in upper right corner.|
Agency conflicts had surfaced already during planning of Landsat 1. NASA is charged with research and development of aerospace technology, not with handling and disseminating earth-resources data. Thus, NASA reached agreement with the U.S. Geological Survey for responsibility of the program's ground segment. In the decades following Landsat 1, the program experienced severe political uncertainty and outright hostility from some segments of the scientific community. Some people viewed Landsat as an expensive toy to produce pretty pictures of limited practical value. Landsat was labelled a "technology in search of an application" (Lauer et al. 1997, p. 833). Kuhn's (1962) prescription for scientific revolutions forewarned of such developmental stages, in which skepticism and denial would take place by whole segments of the science and technology community.
Following success of the MSS, Norwood's group at Hughes built a second-generation scanner, called the thematic mapper or TM, with improved spectral and spatial resolution. It was put into Landsats 4 and 5 in the early 1980s, and once again proved to be a technological and scientific success that greatly exceed design criteria. The TM has provided:
|Left: San Francisco Bay, California. TM bands 1, 3 and 5 color coded as blue, green and red. Right: Mississippi River and delta. TM bands 2, 3 and 4 color coded as blue, green and red.|
|Left: Gaza Strip and Israel. TM bands 2, 3 and 4 color coded as blue, green and red. Right: Nile River and Cairo, Egypt. TM bands 1, 4 and 3 color coded as blue, green and red.|
Government policies designed to transfer the Landsat program from the public to the private sector were seriously flawed. These policies did not result in market growth, were more costly to the federal government than if the system had been federally operated, did not significantly reduce operating costs, and significantly inhibited applications of the data. (Lauer et al. 1997, p. 836)
Under EOSAT, the operation of Landsat was tailored for users that could afford expensive data. Primary users were the military and major oil/mineral companies; academic and governmental users were largely excluded from the high-cost Landsat market. Digital datasets were not routinely archived for many parts of the world, and so many valuable Earth observations were lost. Landsat 6 was designed and built under EOSAT supervision. The satellite suffered a launch failure in 1993; it is presumably somewhere on the seafloor in the South Pacific Ocean (Mika 1997). In the mean time, Landsat 5 continued to function routinely.
Landsat 1 began an era of space-based resource data collection that changed the way science, industry, governments, and the general public view the Earth. For the last 25 years, the Landsat program--despite being hampered by institutional problems and budget uncertainties--has successfully provided a continuous supply of synoptic, repetitive, multispectral data of the Earth's land areas. These data have profoundly affected programs for mapping resources, monitoring environmental changes, and assessing global habitability. (Lauer et al. 1997, p. 831)
Landsat digital images, collected over a 25-year period (1972-1997), are among the most important data assets available to the earth-science community. The EROS Center has archived more than 120,000 gigabytes of these older Landsat MSS and TM datasets (Holm 1997)--see EDC. In fact, Landsat has done much to facilitate development of earth-system science, as an emerging multidisciplinary approach to understanding the Earth's environmental system (Goward and Williams 1997). The success of Landsat spawned many similar earth-resources satellites in the late 20th century by the United States and several other countries (Tatem et al. 2008)--see Table 1.
|1972||Landsat 1||USA-NASA||MSS, RBV|
|1975||Landsat 2||USA-NASA||MSS, RBV|
|1978||Landsat 3||USA-NASA||MSS, RBV|
|1984||Landsat 5||USA-NASA||TM, MSS|
|1993||Landsat 6||USA (Eosat)||ETM||1993 ||SPOT-3 ||France ||HRV||1993 ||IRS-P1 ||India ||LISS-2, MEOSS||1994 ||IRS-P2 ||India ||LISS-2, MOS||1994 ||RESURS-02 ||Russia ||MSU-E||1995 ||IRS-1C ||India ||LISS-3||1996 ||ADEOS ||Japan ||AVNIR||1996 ||PRIRODA ||Germany/Russia ||MOMS||1997 ||CBERS ||China/Brazil ||LCCD||1997 ||IRS-1D ||India ||LISS-3||1998 ||SPOT-4 ||France ||HRVIR||1998 ||IRS-P5 ||India ||LISS-4||1999 ||Landsat 7 ||USA-NASA ||ETM+||1999 ||Ikonos ||Commercial ||High-res MSS||1999 ||Terra ||USA/Japan ||ASTER, etc.|
|Overview of EROS Center, Sioux Falls, South Dakota. Photo date 8/96.|
|Entrance of new wing completed in 1996 for NASA's Mission to Planet Earth program, which includes Landsat 7. Photo date 7/96.|
|Solar panel array and water tower for providing hot water to the photo-processing laboratory. The solar panels were later destroyed by a hail storm. Photo date 7/96.|
Landsat 7 carries an enhanced thematic mapper plus (ETM+), which should provide continuity of Landsat TM data with enhanced spectral and spatial resolution. EDC plans to collect 250 scenes per day in order to assemble a seasonal global archive of data. This will be the first systematic attempt to collect and archive space-based remote sensing to build a worldwide database covering key environmental features. Scenes collected by other international stations will more than double this figure; Landsat 7 will generate nearly 2 terabytes of data per day.
The continuous operation of Landsat for more than 35 years provides a remarkable database for documenting long-term changes in landuse and landcover conditions. NASA has assembled a global, orthorectified dataset of Landsat MSS, TM and ETM imagery representing three epochs: 1970s, ca. 1990, and ca. 2000 (Tucker, Grant and Dykstra 2004). The images are corrected spatially for terrain displacement and satellite viewing geometry, and they have geodetic coordinates. Approximately 7500 scenes are included for the 1970s and a like number for 1990. About 8500 scenes represent 2000. Several hundred scenes are missing from the 1970s and 1990 datasets, primarly because of poor data archives (1970s) and lack of collection (1990). Because the land areas of the Earth are on average 60% cloud covered, it proved impossible to achieve cloud-free conditions for all scenes, particularly in tropical regions.
Beginning in 2008, the EROS Center of the U.S. Geological Survey openned the Landsat data archive to all users free of charge. This represents a tremendous set of earth imagery spanning four decades of environmental change. Access is via Glovis and EarthExplorer. Both Landsat 5 and 7 remain operational, as of 2012, although in severely reduced modes which limit the amount and quality of imagery available for the past few years. The Landsat Data Continuity Mission (LDCM) has entered its final stages of preparation and testing and is now scheduled for launch in 2013 (see links below).
U.S. Geological Survey Landsat homepage.|
Landsat gateway homepage.
Landsat Data Continuity Mission—see LDCM.
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