Landsat 7 starts viewing the the world

Landsat 7 starts viewing the world

New satellite provides double the detail of earlier satellites

April 28, 1999: The Tennessee Valley from just east of Huntsville, Ala., to just west of Atlanta, and north to Knoxville, can be viewed in one of the first Landsat 7 images (right) released by NASA and the U.S. Geological Survey (USGS) on Earth Day.

The Tennessee Valley is home to the Global Hydrology and Climate Center, one of the research institutions that will use Landsat 7's improved imagery. Scientists at the GHCC in Huntsville, Ala. (just barely out of this image to the left), will use Landsat imagery to help analyze urban growth in studies of the "urban heat island" effect around cities, and in searching for ancient Mayan ruins in Central America.

Right: The southeastern Tennessee Valley. The Tennessee River slices through the upper left corner of the image (Lake Guntersville is the large body of water). Chattanooga, Tenn., is visible in the upper middle portion of the image. Links to 850x925-pixel, 184KB JPG. Credit: NASA and USGS.

Left: South Dakota is shown in the first image from Landsat 7. Links to 941x1024-pixel, 243KB JPG.
Right: The Land of Spring Break, Florida's Gulf Coast from Panama City to Pensacola, is shown in a later image. Links to 780x750-pixel, 609KB JPG.

The images shown here are raw frames taken for engineering data. They have not been calibrated, so they might not fully represent the ground scene. Credit: NASA and USGS.

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The first Landsat 7 image was a view of South Dakota, home of the USGS's data center for Landsat imagery. The resolution of the new image is twice as good as previous Landsat images, distinctly highlighting airport runways, dams, cities, rivers and highways. Landsat 7 was launched April 15.

Officials at the Landsat 7 Project have announced that they are"highly pleased with the quality of the ETM+ data received so far." The satellite is gathering data from Earth's land surface and coastal regions. Analysis of the data will provide scientists with new information on deforestation, receding glaciers and crop monitoring.

Landsat 7 carries a new instrument, the the Enhanced Thematic Mapper Plus (ETM+). Previous Landsat satellites carried the Multispectral Scanner (MSS) and the Thematic Mapper (TM) instruments. An MSS was flown aboard every Landsat launched since the first in 1972. The TM was introduced on Landsats 4 and 5. Replacing MSS and TM , the ETM+ greatly improves upon the earlier instruments.

Left: A contrail (condensation trail) from a jet casts a shadow over the American plains. Links to 512x257-pixel, 132KB JPG. Credit: NASA and USGS.

Because of the long history of the Landsat Program, scientists can compare the better calibrated Landsat 7 data with older Landsat images and be able to sort out effects caused by instrument differences as they analyze a scene. This will give researchers improved insight into the 27 year time series of Earth remote sensed Landsat data from previous missions, greatly enhancing the value of the entire archive.

The ETM+ views the Earth in three main sections of the spectrum, four visible and near infrared channels (VNIR, 0.4-1.0 micrometer wavelength), two short wavelength infrared (SWIR, 1.0-3.0 micrometer), and thermal long wavelength infrared (LWIR, 8.0-12.0 micrometer). Resolution of the ETM+ is 15 m (49 ft) in panchromatic (black & white) mode, 60 m (197 ft) in the thermal channel, and 30 m (98 ft) in the rest of the channels.Landsat 7 orbits the Earth at an altitude of 705 km. The orbit is inclined 98.2 deg. to the equator so it's slightly "backwards" compared to the direction of most satellites. This keeps the plane of the orbit oriented the same to the Sun so Landsat always crosses the equator, southbound, at 10 a.m. local time. This means that sunlight will always fall at about the same angle in an image. The orbit also retraces its path every 16 days so scientists can revisit a site.

Web links

Landsat 7 Project home page

Southeast Regional Climate Assessment - from the Global Hydrology and Climate Center

GHCC Home page - Earth, Climate, Hydrologic, and Archaeological studies

Every day is Earth Day for climate scientists (April 22, 1999): GHCC researchers will use Landsat 7 images for a closer look at terra firma

Students to learn what's hot at Earth Day celebration (April 22, 1999): Open house at Global Hydrology and Climate Center

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NASA's Earth Science Enterprise Information on Earth Science missions, etc.

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Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack

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