Weather satellites can be either :- Geo-stationary: they have an orbit synchronised with the rotation of the earth and sit over one spot Polar orbiting: they orbit from pole to pole and with each pass they take images of different sections of the earth In both cases data is sent to a receiving station such as the one at Dundee University and transformed into the images we see
<ul><li>A visible satellite image for June 2003. </li></ul><ul><li>Cloud is shown as white </li></ul><ul><li>The surface of the earth is dark in colour </li></ul><ul><li>The outline of the European coastline is shown </li></ul>
<ul><li>Look at this visible image for May 2003 </li></ul><ul><li>large areas of white are stratus cloud </li></ul><ul><li>blobs of white are cumulus clouds </li></ul><ul><li>clouds in bands relate to fronts </li></ul><ul><li>notice the spiral of cloud </li></ul><ul><li>This white area is the snow of Greenland </li></ul>
Visible satellite images recap <ul><li>Deep cloud that could produce precipitation is bright white </li></ul><ul><li>Thin cloud or low cloud/fog is grey </li></ul><ul><li>Stratus cloud is seen as sheets of white </li></ul><ul><li>Cumulus and cumulonimbus cloud is seen as a speckled pattern </li></ul>
Now : attempt to describe and analyse this image
Satellite images can also be in ‘infra-red’ Visible image Infra-red image
Characteristics of ‘infra red’ images Infra-red images basically pick up heat. The colder it is the brighter the white Deep cloud that reaches the cold levels of the upper troposphere shows up as bright white. This is the precipitation producing cloud Low cloud is not as cold and shows up as grey. This cloud is less likely to produce precipitation The surface is warmest and will be the darkest colour A drawback is that low cloud, fog and the surface may appear similar A benefit is that infra-red imagery works at night!
The same satellite pass in visible and ‘infra-red’ 04.30 am in May Which is which?