Hi,
What you actualy see is a temperature map of the earth for a given time. On the raw images/data cold is represented as white and heat is black. Thus the cold cloudtops appears as white and the heat of the deserts as black. The satellite is measuring the radiation from the surfaces he can see. It can't look through the clouds, so most of the time the white pixels are could cloudtops. But not always. During wintertime over Canada, Northern Scandinavia ans Siberia my look full overcast by clouds. The cause is most of the time very low temperatures over snow or icecover and it will look as upper level high clouds in the sky, because of its very low temperatures. Clouds can't be discriminated from snow, ice or very cold air at the surface in the IR channels. On the other hand over the tropics relative warm clouds (near surface clouds) are hard to see. They are melting/fading in the radiationheat of the tropical sea's, deserts and forests.
What we are seeing is most of the time clouds. The high level cloudtops are used to find front locations (most of time bands of clouds) and thin cirrus. The large ovals in a bands over the tropics are tropical thunderstorms. Low level cloudtops can be used to find locations of fog, stratus and small cummuliform clouds. And very important: We do have an overview of clouds during during the night, where visual images are not very useful.
The used technic for this offered dataset is to remap the full disk images for all the five satellites to a format Celestia can read. Then each pixel on the grey-scale from the IR image is representing a specific temperature. Each grey scale pixel can be recolored in another. This technic is used for the Celestia IR versions and I use the same model for my daily weathermaps. I use the IR images and superimpose the weathermaps on it. Feel free to take a look at my pages and you will see the match of high's and lows with the clouds, but beware; I'm serving the Dutch marked and all is in Dutch. Scroll down to <wereld weer atlas = world weather atlas>. Dutch names for continents and oceans are almost the same as in English, so you will find the way here. This is the best way to show you how we can use the satellite images.
http://www.meteo-maarssen.8m.com/achtergrond/satelliet/satellietfoto.htm
I'm now trying to use the IR images as a kind of speudo visual cloudmap over an earth surfacemap. There are limits: I'm not able to create cloudmaps in layers, but the benefit is that you have a natural look and and IR-look alike for same time, almost each day of the year.
A preview (not operational) is available at:
http://www.meteo-maarssen.8m.com/data/celestia/earth-cl041030.jpg
If you are interest in this stuf, then visit the homepage of David Taylor (Scotland). He is offering all kind of software for use of almost all weathersatellites. His homepage:
http://www.satsignal.net
Look for GeoSatSignal for geostationary satellites as GOES and Meteosat and for SatSignal for the polar orbiters as NOAA. Both programs can handle data from direct satellite readout as from internet sources as well. This is not freeware, but shareware.
Hope this helps,
Cheers,
Ton Lindemann
