Measurements from space
Satellites that circle the globe are able to give us a lot of insight into Earth's weather. They are also very useful in studies of the middle atmosphere.
Most weather satellites have orbits that are designed to maintain their position above a point on the equator (they are 'geostationary'). Although they are able to continuously probe the continents below them, their view of the polar regions is often poor.
Polar-orbiting satellites, however, are continuously moving from pole to pole as the earth rotates beneath them. By passing atop larger portions of the earth, they can be used to photograph or sense a larger part of its surface.
Satellites used in middle atmosphere remote sensing are generally polar orbiting. Their instruments often view Earth's atmosphere sideways.
The portion of the atmosphere that is visible from above the earth's surface against the dark background of space is known as the 'limb'. These satellite instruments use a technique known as 'limb-scanning'. This allows the height of the part of the atmosphere that the satellite is viewing to be worked out. However, these satellites tend to sense large volumes of Earth's atmosphere: although they have excellent global coverage, they do not have high resolution in the horizontal or the vertical.
The TIMED (Thermosphere • Ionosphere • Mesosphere • Energetics and Dynamics) satellite mission is studying the influences of the sun and humans on the middle atmosphere, the least explored and understood region of Earth's atmosphere.
Measurements made by various Space and Atmospheric Sciences projects will benefit from and contribute to the TIMED mission. For more information visit the TIMED spacecraft's website.