How do weather satellites work?

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How do weather satellites work?

Weather satellites carry instruments (not cameras!) that scan the Earth to form images. These instruments usually have some sort of small telescope or antenna, a scanning mechanism, and one or more detectors that detect either visible, infrared, or microwave radiation. These measurements are in the form of electrical voltages that are digitized, and then transmitted to receiving stations on the ground. Most of the satellites and instruments they carry are designed to operate for 3 to 7 years, although many of them last much longer than that.

Almost all weather satellites are put into one of two kinds of orbits around the Earth. One is called a "geostationary" orbit, with the satellite at a very high altitude (about 22,500 miles) and orbiting over the equator. The altitude is chosen so that it takes the satellite 24 hours to orbit the Earth once, which is also the rotation rate of the Earth, so that the satellite appears to be fixed over a single spot - thus the name "geostationary". This type of satellite is what produces the cloud animations you see on TV, and can take images as frequently as every minute or so. The other orbit type is called "polar", where the satellite is put into a relatively low altitude orbit (around 500 miles) that carries the satellite near the North Pole and the South Pole. Unlike the geostationary orbit, the polar orbit allows complete Earth coverage as the Earth turns beneath it. These orbits are usually "sun-synchronous", allowing the satellite to measure the same location on the Earth twice each day, and the same local solar time.

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