NASA has deployed the first major satellite in an unprecedented program to check the health of Planet Earth and understand the complex interactions that drive global change with the April 15 launch of the Landsat 7, the latest mission in the Landsat series, which has been documenting the Earth’s surface for more than a quarter century.
NASA plans to launch six spacecraft over the course of the year dedicated to advancing our understanding of global change. Landsat 7’s role in this effort will be to make global, high-resolution measurements of land surface and surrounding coastal regions.
The diversity of applications makes the Landsat spacecraft unique among Earth observation satellites. Landsat images have been used in everything from measuring the ebb and flow of glaciers and population changes in and around metropolitan areas, to monitoring strip mining reclamation and assessing water quality in lakes. Landsat has been used to monitor timber losses in the U.S. Pacific Northwest, map the extent of winter snow pack, and measure forest cover at the state level.
"We feel that the Landsat 7 spacecraft will dramatically enhance the use of remotely sensed data in our daily lives," said Dr. Darrel Williams, Landsat 7 Project Scientist, at NASA’s Goddard Space Flight Center, Greenbelt, Md.
Every 16 days, Landsat 7 will fly over and document the condition of the entire globe. As far as scientific Earth observing satellites go, Landsat 7 is unique in that the images it collects are extremely detailed – Landsat can "see" features on the planet as small as 30 meters, compared to the geostationary GOES satellites which can only resolve objects of 4 kilometers or greater. So good are the Landsat images that scientists studying volcanoes can actually produce maps of lava flows with pinpoint accuracy.
Landsat 7 marks a new direction in the program to reduce the cost of data and increase global coverage for use in global change research. Every day, Landsat 7 will collect 250 scenes, each one containing enough digital data to fill a powerful home computer’s hard drive. While previous Landsat data were often too expensive for widespread scientific use, all Landsat 7 data received at the main collecting center in Sioux Falls, South Dakota will be archived and available electronically within 24 hours and will be sold at cost.
Scientists use Landsat satellites for some very down-to-earth purposes.
Urban sprawl is one example. Observing urban areas over time with Landsat imagery can show where growth is taking place and help geographers evaluate how different urban planning programs effect population growth and land use. One of Landsat’s 14 scientific teams will use Landsat observations to evaluate growth patterns of cities such as Portland, Ore. (which has strict planning and environmentally sensitive zoning laws) with other cities around the world.
Another group of scientists led by the Department of Agriculture want to use Landsat 7 data to improve on a program to help farmers and land managers increase crop yields and cut costs while reducing environmental pollution.
Scientists from NASA’s partner agency in the Landsat 7 mission, the U.S. Geological Survey, want to use Landsat 7 to spot the amount and condition of dry biomass on the ground, which are potential sources for feeding wildfires that can threaten humans, animals and natural resources.
Landsat 7 was launched on April 15, 1999 from Vandenberg Air Force Base, CA, on a Delta-II expendable launch vehicle. Separation of the spacecraft from its launch vehicle was scheduled to occur about 62 minutes after launch. Once in its final orbital position, the satellite will orbit the Earth at an altitude of approximately 438 miles (705 kilometers) with a Sun-synchronous 98-degree inclination and a descending equatorial crossing time of 10 a.m. The orbit will be adjusted so that it covers the complete Earth every 16 days. This orbit will be maintained with periodic adjustments during the 5-year life of the mission.
The instrument onboard Landsat 7 is the Enhanced Thematic Mapper Plus (ETM+). The instrument is a passive sensor, a type of remote-sensing instrument that measures solar radiation reflected or emitted by the Earth.
The instrument has eight bands sensitive to different wavelengths of visible and infrared radiation. It’s improved from earlier versions. Landsat 7’s Thematic Mapper has better resolution in the thermal infrared band than the instruments carried by Landsats 4 and 5. It is also far more accurate than its predecessors.
The Landsat 7 system will collect and archive an unprecedented quantity of high-quality multispectral data each day. The data will, for the first time, provide a high-resolution view of both seasonal and interannual changes in the terrestrial environment.
The USGS Earth Resources Observation Systems Data Center (EROS Data Center) in Sioux Falls, SD will process, archive, and distribute all U.S. Landsat data. The ground system at the data center in Sioux Falls, SD will be capable of capturing and processing 250 Landsat scenes per day delivering at least 100 of the scenes to users each day.
"The USGS is proud to assume added responsibility for the processing and distribution of Landsat data," said R.J. Thompson, Landsat Program Manager, U.S. Geological Survey. "The Landsat system, conceived originally within the Department of the Interior, is an important dimension of the USGS' role in providing information for science for a changing world."
The Landsat Project Office, located at Goddard, manages Landsat development for NASA’s Office of Earth Science in Washington, DC. Goddard is responsible for the development and launch of the satellite, and the development of the ground operations system. Spacecraft operations will be performed at a Mission Operations Center at the Goddard and at the Earth Resources Observation Systems Data Center. Goddard will operate the spacecraft until Oct. 1, 2000, when this function is turned over to the U.S. Geological Survey.
The spacecraft was built by Lockheed Martin Missiles and Space in Valley Forge, PA. The instrument was built by Raytheon (formerly Hughes) Santa Barbara Remote Sensing in Santa Barbara, CA.
Landsat 7 is part of a global research program known as NASA’s Earth Science Enterprise, a long-term program that is studying changes in Earth’s global environment. The goal of the Earth Science Enterprise is to provide people a better understanding of natural environmental changes. Earth Science Enterprise data, which will be distributed to researchers worldwide at the cost of reproduction, is essential to people making informed decisions about their environment.
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