S'COOL: Measuring Clouds and Energy from Space
Measuring the energy (radiation) given off by the Earth into space is relatively simple. One simply collects the energy that leaves a certain place on Earth (the field of view) and travels to the location of the spacecraft sensor. This energy (voltage) then has to be converted to a meaningful quantity through a complicated process of calibration and inversion. But the measurement itself is straightforward.Measuring clouds from space is more of a challenge. It is done by remotely sensing the energy which is given off within a certain field of view (as above). Once that is done, however, all sorts of logic and thresholds have to be applied to determine whether what the satellite saw was a cloud or not. This complication is due in large part to the fact that the satellite is attempting to detect clouds against a highly variable background (land/ocean, snow/ice, dry/wet ground, vegetated/unvegetated areas, urban/rural, etc). In contrast, detection (though not necessarily identification) of clouds is very simple from the surface, because one views them against the uniform background of space - or of "blue sky". This is one reason why the S'COOL Project may be of great value to CERES scientists: it gives us a widely distributed network of observers who can tell us for sure whether (and also what kind of) clouds were present during a given satellite overpass. This kind of ground truth information then helps fine tune the logic and thresholds so that our detection methods can be improved, even over areas where we have no observers.
More information on remote sensing can be found HERE
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