Land Cover Change Detection Studies Get Huge Boost from Space

For detection and monitoring of changes over large areas, such as deforestation in Brazil, and measuring minute natural changes, such as glacial recession, multispectral imagery (MSI) is the tool of choice. A series of U.S. space satellites, called Landsat, have gathered imagery for change detection studies for the past 26 years. The first Landsat, originally called ERTS-1 (Earth Resources Technology Satellite), was developed and launched by NASA in July 1972. Shortly thereafter, the satellite was renamed Landsat 1 and was followed by two nearly identical sister satellites in January 1975 and March 1978.

In the late 1970s and early 1980s, a second generation of Landsat satellites was developed. Landsat 4 was launched in July 1982, and Landsat 5 followed in March 1984. Landsats 4 and 5 were equipped with two instruments. The Multi-spectral Scanner (MSS-80 meter resolution) was identical to MSS systems on Landsats 1-3 and provided imaging continuity between the platforms. The Thematic Mapper (TM) added more spectral sensitivity (seven spectral bands vs. MSS's four) and sharper spatial resolution (30 meters). Both instruments detect and record electromagnetic (EM) radiation levels of objects on earth. The next successor satellite, Landsat 6, failed to achieve orbit in 1993. Landsat 4 was retired in 1991, and the MSS sensor on Landsat 5 failed in October 1993.

To keep imagery flowing to earth's scientists, planners, environmentalists, and others, Landsat 7 was launched into its orbit on April 15, 1999. This satellite, orbiting some 438 miles above the earth, provides imagery for use by Esri customers worldwide.

Landsat 7's sensor, the Enhanced Thematic Mapper Plus (ETM+), is a derivative of the Thematic Mapper engineered for Landsats 4 and 5 but is more closely related to the Enhanced Thematic Mapper (ETM) lost during the Landsat 6 failure. The primary performance-related changes of the ETM+ over the TMs are the addition of the panchromatic band and two gain ranges (added for Landsat 6), the improved spatial resolution for the thermal band, and the addition of two solar calibrators.

The ETM+ is designed to collect, filter, and detect radiation from the earth in a swath 185 km wide as it passes overhead and provides the necessary cross-track scanning motion, while the spacecraft orbital motion provides an along-track scan.

Landsat 7 is expected to have a design lifetime of five years and provide images for GeoCover-LC 2.0. (See main story about GeoCover-LC 1.0.)

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