The first Landsat satellite, formerly known as the Earth Resources Technology Satellite (ERTS), was launched in 1972 to take images of the Earth's surface. The images have been used to analyze changes on the earth, such as deforestation, sea level rise, droughts, famines, destruction of natural habitats, and urbanization. Landsat-2, -3, -4, and -5 were developed and launched afterwards (Landsat-6 failed to reach orbit). For now, Landsat-5 is currently taking images. Landsat-7 (here is a picture of Landsat-7) was launched on 15 April 1999 out of Vandenberg Air Force Base, California.

How can Landsat images be useful for us?

The earth's environment is always changing. Famines, floods, deforestation, and urbanization are just a few of the negative examples. Since Landsat-7 takes images every 16 days, scientists can use the images to monitor, compare and study these changes in the environment. Although Landsat-7 will cover the entire globe every 16 days, it actually acquires only about 1/3 of the area at a time because of limited processing and storage capacity on the ground and thermal/power constraints on the spacecraft. Some example scenes that would be in high demand include science, agriculture or commerce applications or where change is likely occuring, such as the spring green-up. Landsat-7 also attempts to avoid cloudy areas. With these types of constraints, Landsat-7 will actually take about 3 months to acquire pictures of the entire earth.

How does Landsat-7 work?

Landsat images are obtained through a process called remote sensing. Remote sensing is the process of gathering data from a distance. The images of the earth's surface are taken using a satellite sensor called the Enhanced Thematic Mapper (ETM+). Different objects emit different types of electromagnetic radiation. The TM sensor detects the electromagnetic energy from the objects and records this information in 7 different wavelengths in the form of an image.

Why are Landsat-7 images so awesome?

Landsat-7 takes images of the earth every 16 days.
The ETM+ will take pictures of the Earth 705 km (440 miles) out in space.
Landsat-7 can operate in extremely cold temperature.
Landsat-7 follows instruction from computers on Earth.
Landsat-7 can operate for many years.
Landsat-7 travels around the Earth in 99 minutes (5933.05 seconds to be more precise).
Landsat-7 will provide affordable images (around $500 per image).
Each ETM+ image covers 115 miles on a side.
The pixel size from the ETM+ is 30 m (98.4 ft) for seven bands. However, there is a panchromatic band at a resolution of 15 m (49.2 ft).

Additional information about Landsat-7:

Basic facts about Landsat 7

Detailed information about the Landsat TM sensor can be found at:

http://edcwww.cr.usgs.gov/glis/hyper/guide/landsat_tm

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