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.

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 three primary instruments, the Multispectral Scanner (MSS), the Thematic Mapper (TM), and the Enhanced Thematic Mapper (ETM+). An MSS has been aboard every Landsat since the first one in 1972. The TM was introduced on Landsat 4, and the ETM+ is new to Landsat 7.

By equipping the satellite with copies of older instruments, scientists can compare 27-year-old Landsat images with new images and be able to sort out effects caused by instrument differences as they analyze a scene.

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.