Satellites MET

Satellites can be categorised in two ways: by their orbit height and detector type.

There are two types of satellite orbit.

• Geostationary orbits - as the name implies, these satellites stay over the same point over the earth. This is advantageous in that you can monitor the weather changing over one location, but has two major disadvantages. Firstly, the orbit has to be over the Equator. This means they cannot "see" the poles, and are not very good at detecting weather at high latitudes. Secondly, they have to be a long way away from the earth, and so the resolution is not as good as the other type of orbit.
• Polar orbiting satellites, again, as the name implies, go around the earth over the poles. This means you cannot monitor a weather change as they are moving (although putting more satellites up largely resolves this problem) but it resolves the two problems with geostationary satellites - the satellites travel over the poles, meaning weather can be observed everywhere, and they are much closer to the earth, meaning a higher resolution.

There are three types of detector.

• Visual is exactly the same as your eye - effectively, a camera. This is good for detecting low level cloud, as this will cast a shadow. It is not as good for detecting high cloud as this is generally quite thin. The major disadvantage of visual, however, is that like your eye it does not work at night. Exam questions often put in a time where it would be dark - if so, discount visual as a possibility.
• Infrared detectors look at the amount of heat energy emitted from an area. Ordinarily, this would mean that warmer clouds looked brighter, but infrared images are reverse negatived - meaning that colder areas show up as brighter and whiter. This means that colder, upper level clouds show up the best - cirrus, cirrocumulus and cirrostratus.
• Water vapour detectors look at the amount of vapour in an area. These are mainly of use to specialists predicting when certain phenomena, like tropical revolving storms, will occur. It is unlikely you will get questions on this but they are included for completeness.