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How remote sensing works
TYPES OF LIGHT
Our eyes are sensitive to only a small range of wavelengths in the electromagnetic spectrum, called visible light. Remote sensing satellites use both visible and infrared wavelengths to observe the land surface and atmosphere. Ultraviolet wavelengths are used for some atmospheric observations, and radar sensors use microwave wavelengths.
These two images, collected by Landsat 7 at the same time, illustrate how different wavelengths of light can be used to make alternate images. The left image shows Botswana's Okavango River in visible light. In the right image, the color red was assigned to infrared light. Vegetation growing near the river reflects strongly in those wavelengths.
All images on this page are courtesy National Air and Space Museum
ELECTROMAGNETIC SPECTRUM
Why build satellites to "see" objects in different types of light? Things that appear to be invisible in one kind of light become clear in another type.

ORBITS
Manned missions circle the earth in equatorial orbits, which are between 300 and 500 miles (482 and 804 kilometers) above the surface. Many remote sensing satellites are placed into polar orbits, traveling north and south over the poles. A sun-synchronous orbit is similar but is inclined at an angle to allow a satellite to observe the earth's surface with a constant sun angle. Weather satellites are placed into geostationary orbits, 22,000 miles (36,000 kilometers) above the earth's surface. At this distance, the satellites, "parked" over one spot on the globe, travel around the earth once every 24 hours.
Each orbit serves a different purpose, whether studying large-scale weather phenomena or mapping small details.