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 AURA satellite is an example of a polar orbiting satellite. It hosts limb scanning instruments that sense emissions from the atmosphere in the microwave and infrared bands. Its Microwave Limb Sounder (MLS) provides temperature profiles of the atmosphere to high latitudes.