Landsat Remote Sensing

ES 351, ES 771, ES 775
James S. Aber


Table of Contents
Introduction Applications
Technical characteristics Image processing
Image interpretation References


INTRODUCTION

New earth science methodology

Remotely sensed satellite observations from space have fundamentally changed the way in which scientists study the atmosphere, oceans, land, vegetation, glaciers, sea ice, and other environmental aspects of the Earth's surface. Half a century of satellite observations of the Earth has provided dramatic pictures and is the basis for a new scientific paradigm--earth-system science (Tatem et al. 2008).

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. This is the case with the Landsat system, which was operated commercially by EOSAT during the 1980s and '90s.

A great variety of satellites has been built for monitoring various environmental conditions on land and at sea. Different orbit configurations are used, and satellite sensors can view the Earth in vertical, side, or limb modes. The new methodology of earth science is based on satellite data, which allow a "whole earth" approach to studying the environment. Remotely sensed satellite data and images of the Earth have four important advantages compared to ground observations.

  1. Synoptic view: Satellite images are "big-picture" views of large areas of the surface. The positions, distribution, and spatial relationships of features are clearly evident; megapatterns within landscapes, seascapes, and icescapes are emphasized. Major biologic, tectonic, hydrologic, and geomorphic factors stand out distinctly.

  2. Repetitive coverage: Repeated images of the same regions, taken at regular intervals over periods of days, years, and decades, provide data bases for recognizing and measuring environmental changes. This is crucial for understanding where, when, and how the modern environment is changing.

  3. Multispectral data: Satellite sensors are designed to operate in many different portions of the electromagnetic spectrum utilizing atmospheric windows. Ultraviolet, visible, infrared, and microwave energy coming from the Earth's surface or atmosphere contain a wealth of information about material composition and physical conditions.

  4. Low-cost data: Near-global, repetitive collection of data is far cheaper using satellite sensors than collecting the same type and quantity of data would be through conventional ground surveys.

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.

Brief history of Landsat series (1-6)

Scientific satellite remote sensing of the Earth's surface was initiated at a press conference on September 20, 1966. William Pecora, Director of the U.S. Geological Survey (USGS), and Interior Secretary, Stewart Udall, announced the Interior Department's plans for Earth Resources Observation Satellites (EROS). According to Pecora, the EROS program of the USGS was conceived largely as a direct result of the demonstrated utility of Mercury and Gemini orbital photography to Earth resources studies (Lowman 1999). The Departments of Defense and State were furious, and NASA was cool to the idea of launching an unmanned satellite for civilian remote sensing of the Earth. However, President Johnson, the U.S. Congress, and the public supported this idea. So, NASA began to plan a small satellite early in 1967. Several factors led to the desire for satellite observations of the Earth under the Landsat program (Lauer et al. 1997).

The Interior Department and NASA planned to use special television cameras (return beam vidicons or RBV) as the imaging instruments. In 1968, however, Hughes Aircraft submitted an unsolicited bid to place a new type of imaging device on the satellite (Hall 1992). The Hughes group, led by Virginia Norwood, proposed to use a scanner. Scanners were viewed with great skepticism by most scientists for two reasons. First, the scanner employed a moving part, an oscillating mirror, which was considered unreliable. Second, the scanner was not a full-frame imaging device; it created images from strips. Cartographers were suspicious of the scanner's geometric integrity.

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.

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.

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:

Landsat was an outstanding technological success during its development by NASA. However, the institutional role of Landsat changed in 1982, when its operation was transferred to the U.S. National Oceanographic and Atmospheric Administration (NOAA). NOAA was not particularly happy about this arrangement. Landsat then became a victim of the move to privatize governmental programs. Under the Reagan administration, Public Law 98-365 was passed--the Land Remote-Sensing Commercialization Act of 1984. As a result, in 1986 Landsat operations were turned over to EOSAT, a commercial company that sought to earn a profit from sales of Landsat images and data.

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 Data 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.

Table 1. Landsat type earth-resources satellites of the 20th century. Entries in italics suffered launch failure or did not function in orbit. Adapted from Lauer et al. (1997, table 4).
Year Platform Country Sensor
1972 Landsat 1 USA-NASA MSS, RBV
1975 Landsat 2 USA-NASA MSS, RBV
1978 Landsat 3 USA-NASA MSS, RBV
1982 Landsat 4 USA-NASA TM,MSS
1984 Landsat 5 USA-NASA TM, MSS
1986 SPOT-1 France HRV
1988 RESURS-01 Soviet Union MSU-SK
1988 IRS-1A India LISS-1
1990 SPOT-2 France HRV
1991 IRS-1B India LISS-2
1992 JERS-1 Japan OPS
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.

Landsat 7 and beyond

In 1992, the U.S. Congress passed and President Bush signed legislation that returned future Landsat operations to the public realm, beginning with Landsat 7 in the late 1990s. Landsat was made part of NASA's Mission to Planet Earth program in 1994, and President Clinton established Landsat 7 as a joint program with NASA, NOAA (later dropped out), and the U.S. Geological Survey's EROS Data Center (EDC). NASA built and launched the satellite on April 15, 1999, and flight operations were later turned over to EDC (Williams et al. 1999). The EDC archives all Landsat 7 data.

Overview of EROS Data 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.
All photographs © by J.S. Aber.

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.

The data set ... represents a major achievement in the preservation and availability of global Landsat data for three time periods spanning almost 30 years. It is also the first time a globally consistent orthorectified satellite data set at a spatial scale of tens of meters with highly accurate within-scene and among-scene geodetic accuracy has been available to educators and researchers at minimal cost (Tucker, Grant and Dykstra 2004, p. 321).

About half the scenes were obtained from the EROS Data Center, and the other half were provided by international ground receiving stations: Australia, Brazil, Canada, China, Ecuador, Europe, India, Japan, Pakistan, South Africa, and Thailand. These datasets are provided by NASA at minimum cost via the EROS Data Center, and large blocks of data are available also from the University of Maryland's Global Land Cover Facility--see GLCF.

Landsat 7 gateway homepage.

U.S. Geological Survey Landsat 7 homepage.

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REFERENCES

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ES 351 schedule or ES 771 homepage or ES 775 syllabus

Notice: ES 351, 771 and 775 are presented for the use and benefit of students enrolled at Emporia State University. Any other use of text, imagery or curriculum materials is prohibited without permission of the instructor. All Landsat webpage material © J.S. Aber (2008).