Viewing live weather satellite images

The Geostationary Satellite System

With our equipment in school, we can receive, view and print live weather satellite images. This provides an "eye in the sky", allowing movements and developments of weather systems to be watched locally and globally from a Geostationary satellite.

The European Geostationary satellite currently transmitting to us is called Meteosat. This satellite orbits the Earth at approximately 36,000 kilometres above the Earth's surface and appears to be stationary over a specific point. The Meteosat satellite is at 0° longitude above the equator. It sees the same view of the globe as this:

How still images are obtained from WINSAT 7

Every half hour, our Earth is scanned by the satellite. The data is sent back to a centre in Germany. The global picture is then split into smaller sections which are labelled as shown on the left These images are then sent out by the centre in Germany according to a timetable (rather like the TV programmes on Sky TV) and are picked up by our school satellite dish. We are therefore able to capture still images of the entire globe, or smaller sections of the Earth, to be viewed in school.

How animated images are obtained from WINSAT 7

Because the satellite is stationary, it is possible to create an animation of images as they are received. These are a collection of consecutive stills, run together rather like a short film, so that clouds can be seen moving.

Main types of still images

Visible light images ( labelled "C" images)
A visible light image is formed by the satellite measuring light reflected by the Earth and clouds as it passes overhead.

Thick clouds reflect a lot of sunlight and appear bright white. Thin clouds let some sunlight through. They appear a dull white or grey on the satellite image. Neither land or sea reflect much light from the sun. Therefore, they appear in shades of grey on the satellite image.

Infrared images ( labelled "D" images)
The amount of infrared radiation depends on temperature. A hot object gives off a large amount of radiation. Therefore, infrared images give a measure of the temperature of an object.

Warmer areas, which give off more infrared radiation, appear darker than cooler areas. Normally, the sea appears darker than the comparatively cooler clouds. Higher clouds generally appear whiter than lower rain clouds. This is because temperature generally decreases as altitude increases.

The coastline will often stand out clearly on an infrared image, because of the different temperatures of land and sea. In winter, the sea is often warmer than land, so may appear darker than the land. During the summer, the land is nearly always warmer than the sea, so the land appears a darker shade . A major advantage of infrared images is that they can still be obtained during the night, when visible images are not available!

Water vapour images (labelled "E" images) are not useful for our purposes